NOTES ZA GEOGRAPHY DIPLOMA I AND II

     













OFC  012
FOUNDATION COURSE GEOGRAPHY














Susan R. Gwalema


OFC  012
FOUNDATION COURSE GEOGRAPHY








Susan R. Gwalema
Lecturer
Faculty of Arts and Social Sciences
The Open University of Tanzania














The Open University of Tanzania
P. O. Box 23409,
DAR ES SALAAM.
Tel:  22-2668992/2668820
Fax: 22-2668759
E-mail: vc@out.ac.tz, dvc-ac@out.ac.tz, dvc-rm@out.ac.tz

Website: http://www.out.ac.t

The Open University of Tanzania
Kawawa Road,
P. O. Box 23409,
Dar es Salaam,
Tanzania.



©The Open University of Tanzania, 2009
ISBN   978 – 9987 –  00 – 173 - 6

FIRST EDITION, 2009


All rights reserved.  No part of this publication may be reproduced, stored, in a
retrieval system or transmitted in any form or by any means; electronic,
mechanical, photocopying, recording, or otherwise, without the prior written
permission of The Open University of Tanzania.







 iii
CONTENTS


List of Figures………………………………………………………………...............vi
List of Tables ………………………………………………………………................viii
Introduction to the Unit ………………………………………………....…….…..…ix
References………………………………………………………………………………x
Section One:  Physical Geography                                  1
LECTURE 1:
THE MEANING AND BRACHES OF GEOGRAPHY

1.1 Introduction ………………………………………………………… 3
1.2 The Meaning of Geography ………………………………………… 4

LECTURE 2: THE STRUCTURE AND MATERIALS OF THE EARTH
2.1 Introduction …………………………………………………………. 10
2.2 The Structure of the Earth ………………………………………….. 11
2.3 The Plate Tectonic Theory ………………………………………….. 12
2.4 Movement of Plates and Resulting Landforms ……………………... 13
2.5  Continental Drifting ……………………………………………….. 17
2.6 Classification of Rocks …………………………………………….. 19

LECTURE 3:
INTERNAL GEOMORPHIC PROCESSES AND    
LANDFORMS

3.1 Introduction …………………………………………………………. 25
3.2 Earth Movements …………………………………………………… 26
3.3 Tension and Compression Forces and Features they Produce ……… 27
3.4 Intrusive Volcanic Features ………………………………………… 31
3.5 Extrusive Features of Volcanism …………………………………… 34
3.6 The Lifecycle of a Volcano…………………………………………. 35
3.7 Importance of Volcanic Activity to Man …………………………… 36
3.8 Volcanic Activity as a Hazard ………………………………………  iv
LECTURE 4:EXTERNAL GEOMORPHIC PROCESSES; WEATHERING 
AND MASS MOVEMENT 
4.1 Introduction …………………………………………………………. 39
4.2 Weathering ………………………………………………………….. 40
4.3 Mass Movement …………………………………………………….. 47

LECTURE 5: EXTERNAL GEOMORPHIC PROCESSES; EROSION 
                        AND DEPOSITION
5.1 Introduction …………………………………………………………. 52
5.2 Erosion by Running Water ………………………………………….  53
5.3 Deposition by River Action ………………….……………………... 55
5.4 Features Produced by a River ………………………………………. 56
5.5 Erosion by Action of Waves ……………………………………….. 63
5.6 Erosion and Deposition by Wind Action …………………………… 68

LECTURE 6:  THE STUDY OF SOIL
6.1 Introduction ………………………………………………………... 76
6.2 Soil Profile …………………………………………………………. 77
6.3 Constituents of Soil ………………………………………………...  79
6.4 Soil Physical Characteristics ………………………………………. 81
6.5 Soil Erosion, Soil Conservation and Sustainability ………………... 83

Section Two:  Human Geography                                  89

LECTURE 7:  CONSTITUENTS OF HUMAN GEOGRAPHY
7.1 Introduction ………………………………………………………... 91
7.2 Main Concerns of Human Geography ………….………………….. 92
7.3 People and Environment …………………………………………… 93

LECTURE 8: POPULATION AND DEVELOPMENT
8.1 Introduction ………………………………………………………... 99
8.2 Population Terms …………………………………………………... 1 v
8.3 Population Distribution …………………………………………….  104
8.4 Population Density ………………………………………………… 105
8.5 Overpopulation ……………………………………………………. 106
8.6 Population Controls ………………………………………………... 107
8.7 Population Migration ………………………………………………. 108

LECTURE 9: AGRICULTURE
9.1 Introduction ………………………………………………………... 114
9.2 Subsistence Agriculture…………………………………………….. 115
9.3 Commercial Agriculture ……………………………………………  119
9.4 Agriculture in Tanzania ……………………………………………. 120

LECTURE 10: EXPLOITATION OF NATURAL RESOURCES
10.1 Introduction ……………………………………………………….. 125
10.2 Mining ……………………………………………………………... 126
10.3 Mining in Tanzania ………………………………………………… 128
10.4 Problems Associated with Mining in Tanzania ……………………. 130
10.5 Fishing ……………………………………………………………... 130
10.6 Forestry …………………………………………………………….. 133
10.7 Tourism …………………………………………………………….. 135

LECTURE 11: APPLICATION OF STATISTICAL DATA IN 
GEOGRAPHY
11.1 Introduction ……………………………………………………….. 143
11.2 Sources and Types of Geographical Data …………………………. 144
11.3 Summarising Data ………………………………………………… 145

LECTURE 12: GRAPHICAL REPRESENTATION OF GEOGRAPHICAL
DATA 
12.1 Introduction ………………………………………………………... 152
12.2 Geographic Methods ………………………………………………. 152
12.3 Statistical Maps ……………………………………………………. 1 vi

LECTURE 13: TOPOGRAPHICAL MAP INTERPRETATION
13.1 Introduction ………………………………………………………... 173
13.2 Maps………………. ………………………………………………. 174




LIST OF FIGURES


Figure 2.1:
A sectional View of the Structure of the Earth..…………..
 12
Figure 2.2:
The Boundaries of the Main Tectonic Plates……………...
 14
Figure 2.3: Movement of Plates and Related Features……………………..

15
Figure 2.4: Plate Boundaries, Volcanic Activity and Earthquake Zones ….

17
Figure 2.5: Stages of Continental Drifting …………………………………

19
Figure 2.6: The Rock Cycle ……………………………………………….

22
Figure 3.1: The Formation of various types of Folds ……………………..

27
Figure 3.2: Faults and their Related Features ……………………………..

28
Figure 3.3: Major Intrusive and Extrusive Volcanic Features ……………  32
Figure 3.4: Dykes………………………………………………………….. 33
Figure 3.5: A Sill ………………………………………………………….  33
Figure 3.6: The Structure of a composite Volcanic Cone …………………. 35
Figure 4.1: Exfoliation Domes Formed by Mechanical Weathering  ……... 41
Figure 4.2: Block Disintegration ………………………………………….  42
Figure 4.3: Grikes and Clints ……………………………………………… 44
Figure 4.4: Land Slide …………………………………………………….. 48
Figure 5.1: Features in the Upper course of a River ……………………… 56
Figure 5.2: Cut Spur and Widened Valley ………………………………… 58
Figure 5.3: Bluffs, Flood Plain, Levee and Ox- bowl Lake ……………….  vii
Figure 5.4: Types of Delta ………………………………………………… 61
Figure 5.5: Sea, Shore, Coast and Cliff …………………………………… 63
Figure 5.6: Overhanging cliff, Cave, Blow hole and Geo ………………… 65
Figure 5.7: Headland, Bay, Arch and Stack ………………………………. 66
Figure 5.8: Bar Spit and Tombolo ………………………………………… 68
Figure 5.9: Rock Pedestal, Zeugens and Yardangs ...................................... 69
Figure 5.10: Major Hot and Temperate Deserts of the World………………. 71
Figure 5.11: Barchans and Seif Dunes ……………………………………… 72
Figure 6.1: A Soil Profile …………………………………………………. 78
Figure 7.1: The Branches of Human Geography and Related Fields ……... 92
Figure 8.1: Population Pyramids of Four Population Structure …………… 103
Figure 8.2: Carrying Capacity and Potentials in sub-Saharan Africa ……... 108
Figure 8.3: Pattern of Migration in Africa in 1990s ………………………. 109
Figure 12.1: Choropleth Map ……………………………………………….. 153
Figure 12.2: A Contour Map of Rugunga Village in Western Tanzania …… 155
Figure 12.3: A Flow Line Map ……………………………………………... 158
Figure 12.4: A Pie Chart ……………………………………………………. 161
Figure 12.5: Simple Line Graph ……………………………………………. 162
Figure 12.6: Comparative and Group Line Graph …………………………. 164
Figure 12.7: Simple Bar Graph ……………………………………………... 165
Figure 12.8: A Comparative Bar Graph ……………………………………. 166
Figure 12.9: Divergent Bar Graph .................................................................. 168

Figure 12.10: Population Pyramid Graph of Tanzania 1990 ……………….. 170
Figure 13.1: Measurement of Area ………………………………………... 179
Figure 13.2: Compass Directions …………………………………………. 181
Figure 13.3: Grid Reference ………………………………………………. 183
Figure 13.4: A Cross Section ……………………………………………… 186
Figure 13.5: Rugunga Map Extract ……………………………………….. 1 viii



LIST OF TABLES

Table 11.1 Age Distribution of a Hypothetical Sample …………………. 146
Table 11.2 Calculation of Standard Deviation for Ungrouped Data ……. 149
Table 11.3 The Masses of Students at The Open University of Tanzania.. 150
































 ix
INTRODUCTION TO THE UNIT 

This course aims at providing a basic foundation of Physical and Human
Geography to all students who intend to study Geography and apply such
knowledge for teaching in schools and colleges or use it as a tool in other fields.

The first six lectures of the course are centred on a number of topics, which are
intended to expose you to the meaning of geography and physical Geography.
They include the meaning and branches of geography, the nature and structure of
the Earth, its internal movements and the resultant landforms. The emphasis is on
the instability of the interior of the earth.  The course also explores the effects of
external processes, which take place on the earth’s surface, the aggrading and
degrading processes.

Lecture seven to ten of the course deal with Human Geography. This part focuses
on human beings as the driving force for changes in the environment. As people
struggle to better their living sometimes they improve the environment whereas in
other instances they destroy it. The resultant effects depend on how they interact
with the environment. The level of technology and its application in the society
determines the nature of the interaction and the resulting effects.   
 
The last three lectures are on practical geography. They concentrate essentially on
the application of statistics in geography, graphical representation of geographical
data and topographical map interpretation. Statistics are very important in
geographical studies because a lot of data is collected on phenomena. The data
makes sense when it is summarised. Geographical data can be represented
qualitatively or quantitatively. Areas with similar spatial characteristics on a map
can be shaded with the same colour. In other instances the actual data is
represented quantitatively by using charts and statistical maps. x
You will learn about statistical maps and map interpretation. This will enable you
to represent phenomena and explain the what, where and why of their location in
relation with other phenomena.

REFERENCES


Arber, Nicola, Sue Lomas, Garrett Nagle, Linda Thomson and Paul
Thomson (2000), A2 Geography: Heinemann Educational
Publishers, Oxford.
Bolt, B.A (1988), Earthquakes, W.H. Freeman and Company, New
York
Bowen, A and John Pallister, (2001), A2 Geography, Heinemann
Educational Publishers. Oxford. 
Bradshaw, M. and Ruth Weaver (1995), Foundations of Physical
Geography, Ww. C. Brown Communications, Inc, Chicago
Bunnett, R.B (1990), Physical Geography in Diagrams for Africa (8
th

edition). Longman Group Ltd. Hong Kong
 Clark, Audrey, (1990), Dictionary of Geography. Geographical
Publications Ltd, London
Dura, S.E (1990), Map Reading and Photograph Interpretation for
Secondary Schools “O” Level. ILM Publishers Ltd, Dar es
Salaam.
Fellman J.D Arthur Getis and Judith Getis, (1998), Human
Geography: Landscapes of Human Activities, 6
th
edition. The
MacGrave Hill Companies, Inc.
Kaduma, S (1994), “Issues for Agriculture: Challenges for the 21
st

Century”. In Msambichaka, L.A. H.P.B. Moshi and F.P.
Mtatifikoro (Eds): Development Challenges and strategies for
Tanzania: An agenda for the 21
st
 Century. DSM DUP 91-110
 xi

 McMaster, D.N. (1988), Map Reading for East Africa (4
th
 Ed),
Longman Tanzania Ltd, Dar es Salaam.
Lines, C; Laurie Bowlwell and Anne Fielding Smith (1996), A Level
Geography. Letts Educational, London
Lennon, J. Barnaby and Paul G: Cleves, (1983), Techniques and
Field Work in Geography. UN Winhyman Ltd. London.
Madulu, N.F (2000), “Population dynamics and Natural Resource
Management in Tanzania”. In: Journal of the Geographical
Association of Tanzania NR 28 July 2000 p. 35-55
URT: (1997), Agriculture and Livestock Policy. Ministry of
Agriculture and Cooperatives, Dar es Salaam, January
URT: (1997), Agriculture and Livestock Policy. Ministry of
Agriculture and Cooperatives, Dar es Salaam, January
United Republic of Tanzania (URT); Ministry of Natural Resources
and Tourism (1998), National Forest Policy. Government
Printer; Dar es Salaam
Nagle G and Kris Spencer (1997), Geographical Enquiries: Skills
and Techniques for Geography. Stanley Thornes (Publishers)
Limited 
Young, A (1989), Agro Forestry for Soil Conservation. CAB
International, Wallingford.
White, H; T Kllick, S. Kayizzi-Mugerwa and M Savage (Eds).
(2001), African Poverty at the Millenium: Causes,
Complexities and Challenges. Washington D.C: The World
Bank.


 xii

 Yanda, P.Z. and E.K. Shishira (1999), An Overview of Agricultural
Resources Base, Utilisation and Potential in Tanzania
Mainland. Report Submitted to the Ministry of Agriculture
and Co-operatives, United Republic of Tanzania, Dar es
Salaam
World Bank. (2001), World Development Report 2000/2001:
Attacking Poverty. www.worldbank.org/poverty/
URT, Ministry of Agriculture and Co-operatives: Lake Zone
Agricultural Institute, Maruku Agricultural Research Institute
and Caritas-Kigoma. (1999), Agriculture and Food Security
Survey in Kibondo District. Working Paper No 28, 1999. Dar
es Salaam, December.



 1





SECTION ONE 

PHYSICAL GEOGRAPHY

Lecture One: The Meaning and Braches of Geography
Lecture Two: The Structure and Materials of the Earth
Lecture Three: Internal Geomorphic Processes and Landforms
Lecture Four: External Geomorphic Processes; Weathering and
Mass Movement
Lecture Five: External Geomorphic Processes; Erosion and      
Deposition
Lecture Six:  The Study of Soil






 2















BLANK












 3
LECTURE ONE

THE MEANING AND BRANCHES OF GEOGRAPHY

1.1 INTRODUCTION
This lecture presents to you the meaning of geography and its main branches.
Despite being an interdisciplinary subject, the uniqueness of geography is
portrayed by its role of showing spatial relationships, variations, patterns and
process changes through time. The spatial aspect of the subject is emphasised
by the use of maps and three-dimensional models. Some of these changes take
place very slowly as in the case of rock weathering while other changes take
place rapidly such as mass movements and volcanic eruptions. 

Another aspect of geographic studies is the focus on interactions between the
natural environment and human activities. This course covers both physical and
human geography because the two interact continuously. People are affected by
natural events but people are also a very prominent factor in changing the
natural environment. Human beings can bring changes in relatively a short time
like when they construct new roads.

This lecture provides an introduction to what is actually contained in
geography and it is intended to help you develop awareness of the processes
around you and outside your environment, so that you are able to observe,
record and interpret phenomena as geographers.

OBJECTIVES
 After reading this introductory lecture, you should be able to:
(i) Define geography and differentiate it from other subjects;
(ii)  Explain the various spatial interactions and their resultants;
(iii) Define the main branches of geography;
(iv) Reveal the importance of rays of the sun in the formation of
global patterns of temperature 4
1.2 THE MEANING OF GEOGRAPHY
Geography has been defined by Bowen, et al. (2001), as the study of the
physical and human features of the earth’s surface especially their patterns and
variation in distribution, and of their interrelationships between them in the past
or present. Many patterns of distribution of observable facts are revealed in
human use of the environment. Therefore, geography as a discipline studies the
human environment relationships and the way societies are influenced by their
culture in organising their activities on the earth’s surface. Consequently,
although there are many definitions of geography, its precise definition should
include reference to the earth’s surface.

Geography is an enlightening subject in many fields. It provides information in
solving many economic, social, political, as well as environmental problems.
Nevertheless, it differs from other subjects in that it is a spatial subject.
Geographers investigate, describe, explain and analyse patterns and processes
in space; on or near the Earth’s surface. Geographers study spatial associations
between features of the Earth’s surface such as the association between climate
and vegetation, soils on one hand, and landscape features on the other. For that
reason, the concept of environment is used widely in the study of geography.

An environment is a set of surrounding conditions in which organisms live.
These organisms include humans (Bradshaw and Weaver, 1995:4). The earth is
our home and therefore it is important for us to understand how the earth’s
environments work and how human activities can be performed in harmony
with them. We can recognise a number of major global natural environments
such as the Tropical Rainforests and the Monsoon Forests.

There are also spatial interactions between climate, vegetation and soils. Each
of these three elements in the system affects the others and this is basic to the
concept of ecosystems. Climate is the main determining factor for the type of
natural vegetation cover and the major influence on soil type. It also affects th 5
speed of growth of that type of natural vegetation cover. Furthermore, climate
affects the speed and type of weathering of the parent rock.

Notwithstanding the above, climate itself is controlled by latitude and the
amount of solar radiation. These two are responsible for the global pattern of
temperature making climate the dominant factor within these associations of
climate, vegetation and soils. Temperature is what starts many changes below
and on the earth’s surface.

Spatial patterns and processes on or close to the Earth’s surface – whether
physical or human made, undergo changes overtime. Some changes are rapid
such as volcanic eruptions while others take place slowly as in the case of rock
weathering. We need to bear in mind that even if the process is a slow one, the
change can be significant in the long run. For instance, human process of
migration within regions can be a slow one but gradually, it can cause the
region of destination to be overpopulated while the area of origin can undergo
unplanned population decline.

Geography as an interdisciplinary subject has long been divided into two main
branches: Physical and human geography which are further subdivided into
small, more specialised branches as will be discussed. In addition to these, we
also have another relatively new branch of Geographic Techniques and
Geographical Information Systems (GIS). This branch deals with statistics and
computer applications in geography.

1.2.1 Physical Geography 
This branch of geography is concerned with the study–over time, of the
characteristics, processes and distribution of the natural phenomena in space
accessible to human beings and their instruments–the atmosphere, biosphere,
hydrosphere and the lithosphere (Clark, 1990:239). Physical geography
attempts to explain why certain features are found in some places and absent i 6
others. It also provides reasons for changes of physical features over time and
interactions between humans and the environment. The branch includes two
main areas namely, geomorphology and climatology.

(a) Geomorphology
Is the study of landforms, particularly their origins and development of the
processes responsible for the formation of the surface forms of the earth (geo
means earth and morphology refers to shape).

(b) Climatology 
Is the study of the characteristics and distribution of the world’s types of
climate and of the atmospheric processes responsible for them. It also describes
and explains climates and the role they play in the natural environment,
particularly in soil formation and determination of the vegetation cover.

(c)     Biogeography 
Is an added branch of geography that deals with the study of organic life and
soils and the processes forming them. It is the study of spatial distribution of
plants and animals (excluding human beings) and the processes that produce
the patterns of distribution and of the interrelationships of plants and animals
with their environment over time. Its branches are phyto geography that
concentrates on plants and zoogeography that deals with animals (Ibid, p 38).
Another branch of physical geography is soil geography. The study of soil is
referred to as pedology.

1.2.2 Human Geography 
It is that branch of geography concerned with the study and features and
phenomena in the space accessible to human beings which relate directly to or
are due to people as individuals or in groups their past or present activities and
organisation. It concentrates on the interrelationship of people in space, with
their physical environment and with their social environment, covering spatia 7
and temporal distribution, the organisation of society and social processes on a
local to global scale (Ibid, p 150). Human geography has many subdivisions,
but only four are given below.

(a) Economic Geography 
Deals with the interaction of geographical and economical conditions, with the
production, spatial distribution, exchange and consumption of wealth and with
the study of the economic factors affecting the actual differentiation of the
earth’s surface (Clark, 1990:100). In other words it concentrates on activities
which create employment and generate income, their distribution and processes
responsible for them.

(b) Political Geography 
This is the study of the influence of governments upon people, processes and
activities and the ways in which they change both spatially and temporarily.

(c)      Population Geography 
This is the study of demographic characteristics such as fertility, mortality and
migration change and structure of their spatial and temporal variations. 

(d) Urban Geography 
This is the study of relatively densely built up areas where the majority of the
economically occupied inhabitants are engaged in activities mainly concerned
with secondary, tertiary and quaternary industries in towns or cities. It is the
study of morphology, growth, functions and change of such urban settlements
(Clark, 1990:344). Other branches of human geography are historical, medical
and behavioural geography.

SUMMARY

Geography is the study of physical and human related features of
the earth surface particularly their patterns and variation in
distribution over time. The study of Spartial associations of 
 8





phenomena on the earth’s surface gives geography its distinct
character. Knowledge of spatial interactions between climate,
vegetation and soils is basic to the understanding of many events
that take place beneath as well as on the surface of the earth. Even
abstract events like processes of migration are in one way or
another related to interactions of those three factors. Thus
geographical analysis of phenomena looks at interactions between
both physical and human environments. 

Physical geography is at large the study of Earth environments, the
interactions among them and changes in their conditions over time.
Physical geographers also study how earth environments affect and
are affected by human activities.

Geographers collect data which help them to describe, explain,
predict processes, which can take place in the earth environment.
Maps are very essential for geographers as a tool for locating places
and representing the earth’s features.

Geography is an interdisciplinary subject. It is closely related to
other subjects. For example, geomorphology is related to geology
while remote sensing, statistics and quantitative methods in
geography are studied in engineering. Geographers test ideas about
the natural environment by gathering data at different scales and
analysing them just as scientists analyse samples in laboratories.
Maps are also very useful to geographers in presenting and
summarising data. Other subjects use maps too. Therefore,
knowledge of map making and interpretation is crucial.


 9
EXERCISES


1. Define geography. How does geography differ from other
disciplines?
2. Write short notes on each of the following branches of
geography: Physical geography, human geography, economic
geography, political geography and population geography.
3. Why is knowledge of spatial interactions between climate,
vegetation and soils important for a geographer?
4. Provide concrete examples of both rapid and slow spatial
changes on the surface of the Earth.


REFERENCES


Bowen, A and John Pallister, (2001), A2 Geography, Heinemann
Educational Publishers. Oxford. 
Clark, Audrey, (1990), Dictionary of Geography. Geographical
Publications Ltd, London
Bradshaw, M. and Ruth Weaver (1995), Foundations of Physical
Geography, Ww. C.Brown Communications, Inc, Chicago











 10
LECTURE TWO

THE STRUCTURE AND MATERIALS OF THE EARTH


2.1 INTRODUCTION 
This lecture attempts to explain the origin and processes that take place at the
plate margins and the resulting features. It also explains the validity of the
theory of continental drifting based on archaeological evidences and the theory
of plate tectonics. This understanding is expected to help you appreciate the
environment surrounding us.

We are already aware of the fact that the study of physical geography is based
on the relationships between Earth environments, interactions among them and
changes in their condition over time (Bradshaw and Weaver, (1995:10). The
Earth can be divided into four interacting environments namely; the
atmosphere-ocean environment, solid-earth environment, surface relief
environment and the living-organism environment.  The surface relief
environment results from the interaction between the atmosphere-ocean
environment and the solid- earth environment while plants and animals result
from the living-organism environment. This interaction is responsible for the
formation and degradation of landforms.

The occurrence of earthquakes and volcanic eruptions imply that the interior of
the earth is not stable. These events provide clues to the nature of processes
taking place in the interior of the Earth. Some of the clues reveal that there are
internal movements and that the interior is very hot such that it causes melting
of rocks. One of the most satisfying explanation of internal processes and the
occurrence of earth quakes is best explained by the theory of plate tectonics.
The basic idea which the theory attempts to explain is that the earth’s
outermost part; the lithosphere which actually forms the Earth’s crust consists
of large and fairly stable slabs of solid and relatively rigid rock called plate 11
(Bolt, 1988:4). Each plate extends to about 80km in depth and moves
horizontally relative to adjacent plates floating on softer rocks which form a
semi-liquid zone, known as the asthenosphere.  

The continental and oceanic plates can converge towards each other to form
destructive margins or diverge from each other to form constructive margins.
Where transform faults develop, the margins become conservative and no
outstanding landforms are produced except for earthquakes. The destructive
and constructive zones are associated with the formation of landforms such as
volcanic and fold mountains, trenches and rift valleys. 

OBJECTIVES
 After reading the lecture you should be able to: 
(i) Name and describe the concentric zones of the earth, their
physical and chemical characteristics;
(ii) Describe the concepts of plate tectonic theory and continental
drifting;
(iii) Critically, explain processes at the destructive and
constructive plate margins;
(iv) Name and describe the main types of rocks, indicating the
main characteristics of each.


2.2 THE STRUCTURE OF THE EARTH
The earth is made up of three main parts namely, the core (barysphere), the
mantle (mesosphere), and the crust (lithosphere). Part of the earth’s surface is
the atmosphere which is composed of a mixture of gases and this forms a cover
around the earth. The instability in the Earth’s interior and its resulting features
are well explained by the theory of plate tectonics. A theory is a presumption
which attempts to explain reality.
 12
Figure 2.1:  A Sectional view of the Structure of the Earth

Source: Bunnett, P.B (1990:15)

2.3 THE PLATE TECTONIC THEORY
The theory states that, the earth’s crust consists of several large and some
small, rigid, irregularly–shaped plates which carry the continents and the ocean
floor and float on the asthenosphere, moving laterally, very slowly. Our
knowledge of the earth’s interior helps us to understand the origin of features
found into as well as those found on the surface of the earth. 

Large areas of the outer crushed layer of the earth are made of basaltic rocks
(rich in basalt) very similar to sima (silica and magnesium). Recently, large
areas of newly formed basaltic rocks which form the ocean floor in mi 13
Atlantic Ocean and Indian Ocean have been discovered. These basaltic rocks
are believed to have originated from the earth’s mantle, close to the mid-
oceanic ridges, and have pushed outwards away from them. These discoveries
are an indication that the earths crust is unstable and consist of a series of
plates, which are slowly being pushed apart, away from the zone where they
are formed. 

The sialic rocks, which form the continents, are chiefly made up of silica and
alumina minerals. These are carried on the slowly moving plates. Arbar, et al,
(2000:25) attributes movements of plates to convection movements in the
asthenosphere. The Lithosphere (solid rock), which includes the crust, is very
hot with an average temperature of about 1300° Celsius at a depth of 80 km.
The inner core is also solid rock with average temperature above 5000°
Celsius. In between the lithosphere and the mantle is the asthenosphere, which
is partly melted. The difference in the temperature of the two layers of solid
rock is what sets up convection movements. How all this happens is explained
bellow.

Close to the earth’s surface, the upward movements in the asthenoshere spread
out horizontally. These lateral movements cause the crust to split. This in turn
makes the vast continental plates move slowly. In some places, they are pulled
apart, in others pushed together and sometimes they slide sideways. Where
plates separate, plates break apart, forming rift valley faults and Block
Mountains as in the case of the African Rift valley. Further movement is
responsible for sea floor spreading.

2.4 MOVEMENT OF PLATES AND RESULTING LANDFORMS
Convection currents in the asthenosphere rises, separates and forms a mid
ocean rift. The convection current sinks again where the oceanic plate meets
the continental plate. At the edge of plates, adjoining plates come in contact
thereby causing friction which result into large deforming (or tectonic) force 14
that operate on the rocks causing physical and chemical changes in them. This
implies that geological structure of rocks is most affected at the plate margins.                              

At the edges of a plate, the crust is weak and molten rocks try to force their
way to the surface. Movements of the plate edges are felt as earthquakes. The
theory of Plate tectonics thus helps us understand the origin of earthquakes and
volcanoes as well as their associations. The movement and collision of the
plates is referred to as Plate Tectonics. Destructive plate margins are also areas
of intense seismic activity.

In some places, the continental and oceanic plates meet each other at an oblique
angle such that they avoid collision and subduction cannot occur. When this
happens, the plates jerk forward and move again. Each horizontal change can
cause earthquakes along a destructive plate margin. Consequently, earthquakes
are also associated with subduction regions (where plates sink).

Figure 2.2:  The  Boundaries of  the Main Tectonic Plates
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Source: Bunnett, P.B (1990:16)

When an oceanic plate and a continental plate move towards each other, the
edge of the oceanic Plate is drawn underneath the edge of the continental plate.
As it sinks, it carries some of the solid rocks downwards into the asthenospher 15
where they melt and finally get absorbed into the mantle. The region where the
rocks from the edge of the ocean plate are carried down is known as the
subduction zone. Active zones of subduction occur off the coasts of Japan,
California and the West coast of South Africa (Burnett, 1990: 15). (See figure
2:2).

In zones of subduction, the edge of the oceanic plate is bent down into the
mantle when the continental plate pushes up over it. This causes a trench to be
formed, such as the Java Trench. Gradually, sediments from the continent fill
up the trench, but because the plate continues to approach, the sediments are
crushed and folded. These may give rise to a range of fold mountains or a chain
of islands (Figure 2.3). For example as the Indian plate met the Asian plate, it
pushed and folded the sediments up to make the Himalayan Mountains. 

Figure 2.3:  Movement of Plates and Related Features
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Source: Bunnett, F.B (1990: 16).  A mid-oceanic ridge forms when two oceanic plates move apart; a
trench and related fold mountains form when an oceanic plate and a continental plate collide

When molten rock (the magma) swells up from the mantle to fill the oceanic
trench, the magma slowly cools and forms a new crust. Often, violent volcanic
activity takes place as the magma continues to fill the trench and gradually
forms mountain ridges. The mid-Atlantic ridge is being formed in this way 16
Melted rocks from the asthenosphere continually rise at the mid-ocean ridges,
spreading out and hardening to form new ocean floor on either side of the
ridge. This is what is referred to as sea floor spreading. Plates move at a
uniform speed, getting older as they move further away from the ridges.  It is
for this reason that, mid-oceanic ridges are called spreading zones.  This
principle helps to explain the theory of continental drift.

The subduction region is also called a constructive region because molten
magma rises from the mantle and reaches the surface as basalt, which adds new
crystal material on the Earth’s surface. At the zone of construction, plates are
being pulled apart by diverging convection currents in upper mantle. When two
plates move in different directions, tension builds up and fractures are created.
It is through these that magma being forced up by convection currents, reaches
the surface as lava (newest rock). When volcanic rocks reach the surface they
make volcanic islands. Constructive margins are located in the mid–Atlantic,
eastern Pacific and central Indian Ocean. 

 The diverging plates cause rifting as the solid basalt splits and fractures into
many parallel cracks, which run along the top of the ridge. Magma from the
mantle is forced into the cracks as they develop and solidifies to form intrusive
features of volcanism.

Rifting at the constructive margins causes earthquakes and rift valleys. Ocean
ridges and volcanoes also form at these margins as in the case of the East
African Rift Valley which holds lakes lake Tanganyika (5000m deep), Lake
Nyasa and Lake Rudolf but associated with volcanoes such as Mount, Kenya,
Mount Meru and Kilimanjaro, the highest Mountain in Africa. The association
between plate boundaries, volcanoes activity and earthquake zones is well
illustrated in figure 2.4.
 17
When two plates approaching each other collide, the sediments are crushed and
folded. These may give rise to a range of mountains or chain of Islands. For
example, as the Indian plate met the Asian plate, it pushed and folded the
sediments up to make the Himalayan Mountains.

Figure 2.4: Plate Boundaries, Volcanic Activity and Earthquake Zones
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Source:  Adapted from Lines, C. et al. 1999:66

TAKE NOTE


A mid- oceanic ridge forms when two oceanic plates move apart. A
trench and related fold mountains form when an oceanic plate and a
continental plate collide. The heavier oceanic crust sinks or sub
ducts below the lighter continental crust. When the continental
plates collide, the edges are not bent down into the mantle. Instead,
they crumple and fold into mountain ranges due to compression.

2.5 CONTINENTAL DRIFTING
The theory was first postulated in 1858, and then re-stated by Alfred Wegenar
in 1911. It advances that the present distribution of the continental masses is
the result of fragmentation of one or more pre-existing masses which have
drifted apart, the intervening hollows having become occupied by the oceans
(Clark, 1990:71).
 18
Evidence suggests that South America and Africa had been one landmass as
they are of identical ages, supported by reliable fossil evidence and radioactive
dating. Moreover, there are similarities in many mineral and glacial deposits.
Very old rocks, some over 2000 million years old, are found in both Guyana
and the Sahara (indicating that at one time they were in the same region). The
geological column for S.E. Brazil is also similar to that of S.W. Africa. Both
regions have similar mineral deposits such as diamonds as well as coal.
Therefore, today there is no doubt that continents had drifted from their
original location. The mechanisms of the movement came to be understood in
the 1960s and thereafter by the development of the theory of tectonics. Thus
the theory of continental drift provides the evidence whereas the theory of plate
tectonics provides the explanation.

2.5.1 Mechanism of the Movement of Continents
The mantle rock is under great pressure such that it is capable of flowing. The
driving force for these currents is heat from the Earth’s molten core. These
convection currents carry mantle material up to the centre of the ocean ridges
from which new material is added to the Earth’s crust. The material pours out
through the fracture created by the two plates that move apart. As the plates do
so, they carry the continents with them (Bowen et al. 2001.72).

Thus continents have drifted from their original place by lateral earth
movements. The drifting has caused continents, which drifted from one latitude
to another to experience climatic changes. For instance there is evidence of
glacial deposits and coral limestone in Greenland. It is continental drift that can
satisfactorily explain these climatic changes. That means the present climate of
these places is not what it used to be. Such places had moved from their
original places. It is now possible to match rock types in West Africa with rock
types in Brazil. These two regions may have been part of one region some time
back.
 19
2.5.2 The Origin of Continents
Bunnett (1990) stresses further, that there are evidences that the present
continents originated from one Super continent, which Wegener called Pangea.
The northern part of Pangea is called Laurasia and the southern part–
Gondwanaland. It is believed that Africa developed from Gondwanaland, and
the breaking began in the Cretaceous era (Refer to figure 2.5).

Figure 2.5:  Stages of Continental Drifting
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Source: Bunnett, F.B. 1990:26

2.6 CLASSIFICATION OF ROCKS
Apart from internal processes, which take place in the interior of the Earth,
there are others that take place on the surface of the Earth’s surface. Thus the
surface of the Earth is continuously changing its form and the rocks that make
up the surface. Three kinds of rocks can be identified based on their mode of
formation namely, Igneous, Sedimentary, and Metamorphic.

2.6.1 Igneous Rocks
The term igneous comes from the Latin word Ignis which means fire. Igneous
rocks are produced from heated rock, but most igneous rocks are produce 20
deep underground and they are of two main types; namely Plutonic and
Volcanic. Plutonic rocks are formed when the magma does not reach the
surface. It solidifies deep in the crust producing a variety of geologic structures
such as batholiths and dykes which are exposed on the surface by prolonged
action of erosion. Plutonic rocks are also called intrusive igneous rocks.  

Volcanic rocks which are poured on the Earth’s surface are called lava. The
lava that reaches the Earth's surface through volcanoes or through great fissures
hardens and become igneous rock. These are also called extrusive igneous
rocks. Some of the more common types of extrusive igneous rocks are lava
rocks, cinders, pumice, and volcanic ash and dust. 

The nature of cooling of the magma determines the characteristics of the rocks
formed. When molten rock from the asthenosphere, cools and solidifies deep
beneath the surface of the Earth they form crystals on cooling and the rocks are
called crystalline rocks. If the molten rock cools very slowly underneath, the
large crystals have time to grow such as those of granite rock. On the other
hand, if magma cools quickly on the Earths surface the crystals are too small to
be seen, such as those of basalt. 

TAKE NOTE

Rock that moves into the crust towards the surface is called magma.
If it reaches the surface it is called lava. Igneous rocks occur in
layers and do not contain remains of plants and animals.

2.6.2 Sedimentary Rocks
Most sedimentary rocks are formed from sediments deposited either by water,
wind or by ice. The particles accumulate in layers or strata and with time they
are hardened by compression and turned into rock. These are also called
stratified rocks. Some particles accumulate in lakes and seas such as sandstone,
which comes from other rocks that are broken down by weathering and
erosion. Other sedimentary rocks come from the remains of animals and plants 21
Chalk and other limestone are made of the shells and bodies of sea creatures.
Coal forms from the remains of trees.

TAKE NOTE


All sedimentary rocks are non-crystalline and many contain fossils

Three types of sedimentary rocks are recognised: 
(a) Mechanically formed sedimentary rocks: are deposited by water, ice, or
wind. They include clays, gravels, and alluviums (deposited by water),
moraines, boulder clay, boulder clay and gravels (deposited by ice), and
loess (deposited by wind).

(b) Organically formed: are formed from plants (peat, coal and lignite) and
animals (chalk and coral).

(c) Chemically formed: These include potash, gypsum, nitrates, certain  types
of limestone and rock salt.

2.6.3 Metamorphic Rocks
Solid rock can be changed into a new rock by stresses that cause an increase in
heat and pressure. There are 3 main agents that cause metamorphism through
increase in temperature, pressure, and chemical changes. 

Temperature increases can be caused by layers of sediments being buried
deeper and deeper under the surface of the earth. As we descend into the earth
the temperature increases about 25 degrees Celsius for every kilometre that we
descend. The deeper the layers are buried the hotter the temperatures become.
The great weight of these layers also causes an increase in pressure, which in
turn, causes an increase in temperature which in turn brings chemical changes.

The descending rock layers at subduction zones cause metamorphism in two
ways; the plates sliding past each other causes the rocks coming in contact wit 22
the descending rocks to change. Some of the descending rock melts because of
this friction. When rock melts it is then considered igneous not metamorphic,
but the rock next to the melted rock can be changed by the heat and become a
metamorphic rock. Refer to figure 2.6 for the rock cycle.

Factors that cause chemical changes contribute to the formation of
metamorphic rocks. Very hot fluids and vapours can, because of extreme
pressures, fill the pores of existing rocks. These fluids and vapours can cause
chemical reactions to take place that over time can change the chemical
makeup of the parent rock. Metamorphism can be immediate as in the shearing
of rocks at plate boundaries or can take millions of years as in the slow cooling
of magma buried deep under the surface of the Earth. 

Figure 2.6: The Rock Cycle









Source: http://volcano.und.edu/vwlessons/lessons/metrocks.  Accessed on 12 04. 2007

SUMMARY


The earth is made of three main parts, the core, the mantle and the
crust. The crust consists of plates. These are continental and
oceanic plates, which are slowly moving laterally. Some are
converging while others are diverging.

When a continental plate and an oceanic plate move towards eac 23


other (converge), a trench or deep is formed. Fold Mountains and
volcanic activity may also take place at the convergence zone.
Usually a fold mountain range forms when two continental plates
converge while a trench may form when two plates diverge. If this
takes place on the ocean floor, lava pours out to produce oceanic
ridges. These movements of plates cause crevices to form into the
crust through which magma oozes out. They are therefore
responsible for volcanic eruptions and earthquakes. When the
plates move apart beneath a continent, then a rift valley may form.
Horizontal movements are responsible for continental drifting. 

The rocks that compose the crust are classified into three groups:
igneous, sedimentary, and metamorphic. Any rock can be changed
into a metamorphic rock if exposed to prolonged heat and pressure.
Rocks can also be classified according to age. They are given
names according to the period during which they were formed. The
bedrock of Africa is very old and belongs to the Precambrian
rocks. Fold Mountains belong to the Mesozoic rocks while the
volcanic rocks of East Africa belong to the Cainozoic rocks.

EXERCISES 
1. Name and explain the main characteristics of the concentric
zones of the Earth.

2. Explain the concept of the theory of plate tectonics.


3. What do you understand about the theory of continental
drifting?

4. Give an analytical explanation of processes which take place
at the plate margins.

5. Explain the formation of three main groups of rocks and
distinguish their main characteristics 24




6. (a)   Explain how and why fold mountain ranges are formed
along destructive plate margins.

7. (b)  Why are ocean ridges associated with constructive
margins and ocean trenches with destructive margins?

REFERENCES

Arber, Nicola, Sue Lomas, Garrett Nagle, Linda Thomson and
Paul Thomson (2000), A2 Geography: Heinemann
Educational Publishers, Oxford.
Bolt, B.A (1988), Earthquakes, W.H. Freeman and Company,
New York
Bowen, Ann and John Pallister (2001), A2 Geography:
Heinemann Educational Publishers, Oxford.
Bradshaw, M. and Ruth Weaver (1995), Foundations of Physical
Geography, Ww. C.Brown Communications, Inc, Chicago
Bunnett, R.B (1990),  Physical Geography in Diagrams for Africa
(8
th
 edition). Longman Group Ltd, Hong Kong
Clark, Audrey (1990), Geography Dictionary, Geographical
Publishers Ltd.
Lines, C; Laurie Bowlwell and Anne Fielding Smith (1996), A
Level Geography. Letts Educational, London.






 25
LECTURE THREE

INTERNAL GEOMORPHIC PROCESSES AND
LANDFORMS

3.1    INTRODUCTION
Internal geomorphic processes are produced by internal forces, which operate
within the crust. These forces can be divided into two, Earth movements and
volcanic eruptions.

Earth movements operate either vertically or horizontally.  Vertical movements
are up and down. Both movements cause the crustal rocks to fault to form
plateaus, Block Mountains, basins and sometimes escarpments. Horizontal
forces cause sideways movements, which render the crustal rocks to fold, thus
forming fold mountains, rift valleys and at times Block Mountains. Such
movements take place slowly. 

When the magma solidifies in the crust, internal features such as dykes, sills,
batholiths and lacoliths are formed. When the lavas reach the surface they
produce external features such as lava flows, lava plateaus, geysers and
volcanic cones. These movements are often rapid.

In this lecture you will learn how internal forces in the form of crustal
movements give rise to the formation of various landforms that are embedded
into the Earth’s crust as well as those that are produced on the surface of the
earth.

OBJECTIVES

After reading this lecture you should be able to:
(i) Identify major characteristics of lateral and vertical forces.

 26



(ii) Explain causes of vertical and horizontal forces in order to
balance the forces within the earth crust.
(iii) Explain the formation of landforms e.g. fold, block and
volcanic mountains, ridges faults and rift valleys
(iv) Account for the significance of landforms resulting from
internal forces
(v)  Determine the origin of earthquakes and their impact on the
Earth surface.
(vi) Distinguish various types of volcanoes
(vii) Describe main landforms resulting from volcanic processes.

3.2 EARTH MOVEMENTS
An earth movement is a movement of earth’s crust arising from disturbances in
the earth’s interior including both the slow and sudden movements (Clark:
1990 p.98). Major features such as mountains, plateaus and plains have been
formed by both lateral and vertical earth movements.

Earth movements cause sedimentary rocks to be displaced, so that rocks are
tilted or inclined. These movements also cause sedimentary rocks to fold and
fault. Lateral forces of compression cause folding while either lateral or vertical
forces of tension or compression cause faulting depending on the nature of the
rocks being acted upon.

3.2.1 Formation of Folds
When compression forces act in an area of sedimentary rocks, rock layers are
forced to bend up and down. The upper part is called an upfold or anticline
while those which bend down form a downfold or syncline. The sides of a fold
are called limbs. If compression continues, a simple fold can be changed into
an asymmetrical fold where one limb is steeper than the other. Further
compression can lead into an over-fold and finally an over-thrust as shown in
figure 3:1 27

Figure 3.1:  The Formation of various types of Folds
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Source: Bunnett, F.B (1990:24)

3.2.2 Formation of Faults
A fault is a fracture or break in a series of rocks along which there has been
vertical or lateral movement or both as a result of excessive strain.  Tension
forces (forces that act away from each other) cause normal faults while
compression forces cause reverse faults. In addition, lateral movements may
produce tear faults. Escarpments (fault scarps) develop if upward or downward
movements of adjoining crust parts accompany faulting.

Normal faults are those in which the rocks on one side have slipped down
relative to the other whereas reverse faults are those where rocks have been
pushed up. Overthrust faults develop where the plane is near the horizontal.

3.3 TENSION AND COMPRESSION FORCES AND FEATURES
THEY PRODUCE
Formation of features as a result of tension and or compression is well
elaborated by Bunnett (1990). He examines that rocks of the crust are subjected
to tension and compression when vertical or lateral earth movements take
place. When one part of the crust is compressed, another part is stretched thu 28
comes under tension. It is when rocks are under tension that they usually fault.
When they are under compression they may either fold or fault depending on
their capacity to withstand stress. Weak rocks tend to fault whereas flexible
ones fold. It is quite rare for faults to occur singly. More often they occur in
series.

Figure 3.2: Faults and their Related Features
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Source:  Bunnett, F.B  (1990:25)

3.3.1 Earthquakes
An earthquake is a sudden shaking of the ground or vibrations in the earth’s
crust caused by deep-seated disturbances which produce a series of elastic
shock waves spreading out from the epicentre. An earthquake usually
originated from sudden adjustments in the crust of the earth, particularly by
movement along faults or as a result of volcanic activity. Where there are no
volcanoes to act as safety outlets, most several earthquakes are associated with
fault lines (Clark, 1990:98). Thus movement of plates largely causes
earthquakes.

Many earthquakes occur where immense stresses build up either where crustal
plates collide along destructive margins, or where plates grind past each other
along conservative margins. When two plates are subducted into the ocean
trench, the tremendous friction arising from the rocks that are forced agains 29
other rocks generates earthquake shocks. Therefore, the subduction zone is the
region of a series of foci from which earthquakes originate. 

Constructive margins also generate earthquakes because of the stress and
tension which build up in the crustal material when two plates move apart.
However, the scale and intensity of the movement are lower than at the
destructive margins.

Close observation from the map indicates that majority of earthquakes occur in
narrow belts which mark the boundaries of tectonic plates. Shortly, the main
regions where they occur are:
• The mid-ocean ridges
• The oceanic deeps and volcanic islands
• Regions of crustal compression e.g. in N. Africa

3.3.2 The effects of Earthquakes
Bunnett (1990) identifies four main effects of earthquakes as given below:
• Displacement of parts of the earth’s crust either vertically or horizontally

• Raising or lowering parts of the sea floor to form raised beaches. For
instance the Agdir earthquake in Morocco in 1960 raised the sea floor off
the coast. In some areas the depth of the sea decreased from 400 metres to
15 metres after the earthquake.

• Raising or lowering coastal rocks. In  the Alaskan earthquake of 1899,
some coastal rocks were raised by 16 metres.

• Land sliding and opening up deep cracks in the surface rocks. The El
Asnam earthquake in Algeria, in 1954 destroyed an area of 40 km in radius
and opened surface cracks up to 3 metres deep.

Apart from the effects mentioned above, earthquakes are hazard to human
beings and their property. The shocks destroy buildings in villages, towns an 30
cities and sometimes lead to loss of life as the one that occurred in Morocco
early 2004. In December 2004, Asian countries such as Indonesia and Thailand
were devastated by Tsunami which was caused by Earthquakes which occurred
in the Indian ocean.

3.3.3 Measurement of Earthquakes
An instrument called Seismograph measures the intensity of an earthquake.
The instrument records the vibrations produced by an earthquake. The Richter
scale measures the magnitude of an earthquake. The scale ranges from 0 to 8.9.
An earthquake with magnitude of 2.0 is ten times greater than 1.0 and one of
5.0 is 10,000 times greater than an earth of magnitude 1.0. The magnitude of an
earthquake is the total amount of energy released. The intensity of an
earthquake refers to the effect produced by the earthquake. This varies from
place to place, but the magnitude doesn’t change.

Volcanic Activity: vulcanicity refers to all the various ways by which molten
rock and gases are forced into the earth’s crust and on the earth’s crust and on
the earth’s surface. Vulcanicity therefore includes volcanic eruptions, the
formation of intrusive features such as batholiths, sills and dykes into the crust.
 The rocks in the asthnosphere have very high temperatures but great pressure
exerted on them by the crust, keeps the rocks in a semi solid state. High
temperature coupled with a reduction in pressure caused by faulting and
folding forces these rocks to become molten and semi fluid. Molten rock is
called magma. It is a combination of lava and volcanic gas. As the magma
rises, it forces its way into the cracks of the crust. However, if it does not
manage to come out at the earth’s surface, it solidifies in cavities and fissures.
If it pours out on the earth’s surface it becomes lava.
 31
The type of magma and its chemical composition determines the intensity of a
volcanic activity. When the proportion of silica in the lava is below 55%, gases
easily escape; the basaltic lava is fluid and very hot. Eruptions are usually non-
violent and flow for long distances before cooling. Magma that rises from the
subduction zones at destructive plate margins contains silica between 55-70%
and thus the lava is very viscous and explosive. When magma cannot escape
easily, it explodes. This breaks the lava into pieces that are thrown out as
volcanic bombs, ash or dust.

TAKE NOTE

Viscosity is the stickiness of the lava or its resistance to flow. It
increases as lava spreads from the vent cooling. Rhyolite with over
70% silica is the most viscous larva of all.


As the eruption ends the remaining viscous lava often oozes out of the vent and
accumulates up as a dome above it. Thus volcanic cones, which form along
destructive margins, have tall cones with steep sides. The cones are composed
of a mixture of lava flows and beds of ash and hence are called composite
cones.
 3.4 INTRUSIVE VOLCANIC FEATURES
Most of the magma upwelling from the mantle cools and solidifies within the
crust. It is forced into or between rocks, thus it has intruded into the pre-
existing rocks. The resulting features from this activity include batholiths,
laccoliths, dykes and sills.

3.4.1    Batholith 
This is a very large dome-shaped mass of rock usually of granite, formed by a
large–scale, deep-intrusion of magma. Batholiths may form surface features
only after being exposed to the surface of the earth by denudation.
 32
Figure 3.3: Major Intrusive and Extrusive Volcanic Features
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Source: Bunnett, F.B (1990:42) 

Sometimes batholiths resist erosion and stand up as uplands as for instance, the
Chaillu Massif in Gabon, which rises to about 1500m in Mant Iboundji.

3.4.2 Sill 
Is an intrusion of igneous rock of a tabular form resulting from very fluid
magma when it is forced between the bedding planes of sedimentary or
volcanic formations. Sills may form ridges similar to escarpments when they
are exposed by erosion 33
The Three Sisters in Cape Province of South Africa have sill cappings. Some
sills lie across riverbeds where they form water falls. The Kinken Falls near
Pita in the Futa Djalon of Guinea are formed in this way.

Figure 3.4: Dykes  
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Source: Bunnett, F.B (1990:43)

Figure 3.5:  A Sill
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3.4.3 Dyke
This is a feature which is produced when magma cools in vertical or inclined
fissures. Some are easily eroded while others are resistant to erosion If it
happens that a dyke is easily eroded, it forms a shallow trench. If it resist 34
erosion, it stands up as a wall-like ridge and may cause waterfalls or rapids.
The Howick Falls on the River Mgeni in South Africa are a result of a dyke
that stands across it. 

3.4.4 Laccolith 
This is a dome-like shaped mass of igneous rock produced by more viscous
lava when it pushes up the overlying strata and solidifies between layers. When
these intrusive features are exposed on the surface of the earth, they reveal
landforms of interest to geomorphologists. The features also have an impact on
human activities e.g. in construction.

3.5 EXTRUSIVE FEATURES OF VOLCANISM
Usually only a small proportion of the magma that tries to force its way
upwards through the crust manages to extrude out the surface of the earth as
lava. It either erupts from volcanic craters or pours out along fissures. Extrusive
volcanic features include volcanic mountains, lava plateaus, geysers, mud pools
and hot springs. If magma emerges onto the earth’s surface through a vent
(hole) it, usually builds up a volcano which is cone shaped. If it emerges from a
fissure (crack), it may build up lava plain or a lava plateau.

3.5.1 Vent Eruptions
Volcanic eruptions are strongly influenced by the type of magma that escapes.
Some eruptions are explosive such as Mt. Etna in Sicily in year 2001 while
others are gentle such as Mt Kilauea in Hawaii islands. A volcanic cone may
consist of lava, or a mixture of lava and rocks derived from the crust by molten
magma. It may also consist of ash and small fragments of lava (cinders). The
shape and size of the cone is largely dependent on the nature of the material it
consists, and the type of eruption. The channel through which the lava escapes
is called the pipe and the crater is its exit.


 35
3.5.2 Lava Cone
Fluid lavas usually give rise to gently sloping cones such as Nyamlagire, near
Lake Kivu in the Democratic republic of Congo and Mauna Loa in Hawaii.
Viscous lavas produce steeply sloping cones. Due to thickness sometimes the
magma plugs the vent to build a plug dome e.g. those of Atakor volcanic area
of the Hogger Mts. of Algeria. 


Figure 3.6: The Structure of a composite Volcanic Cone
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Source: Bunnett, F.B (1990:45)


3.6 THE LIFECYCLE OF A VOLCANO
Volcanoes pass through three stages; active, dormant and extinct. In the early
stage eruptions are frequent and the volcano is said to be active. During the
period when the eruptions become infrequent, the volcano is said to be dormant
(sleeping) such as the Oldonyo Lengai in Arusha region Tanzania, and the
Cascade volcano of North America. Extinct volcanoes are those that are
unlikely to erupt again (Aber, et al; 2000:25). Mount Kilimanjaro is such an
example 36
3.7 IMPORTANCE OF VOLCANIC ACTIVITY TO MAN
The lava which is poured onto the earth’s surface contains a variety of minerals
some of which are important to the growth of plants. Volcanic soils are known
for their good fertility and hence suitable for agriculture. A good example is the
slopes of Mt. Kilimanjaro and Mt. Meru in Tanzania which for this reason,
support dense populations.

Hot springs in volcanic regions may be used for central heating and production
of electricity as in New Zealand. Hot springs occur at Majimoto in Serengeti
district, Tanzania. Moreover, some hard volcanic rocks are used for building
structures. In Tanzania such rocks are found in Kilimanjaro region.

3.8 VOLCANIC ACTIVITY AS A HAZARD
Volcanic eruptions are a natural hazard (a threat) to man and property. When
an explosive eruption takes place in a habited area, it can destroy buildings,
cover roads, kill people and animals, destroy farms etc. A good example is an
eruption of a Mountain at Goma in Eastern Congo (in 2002), which forced
residents to vacate the town with some casualties.

SUMMARY



Internal forces in the Earth crust are responsible for the formation
of landforms such as mountains, plateaus, plains and valleys.
Tension forces which act away from each other, cause rocks to
fault. If faulting is accompanied by upward and down ward
movements Block Mountains, rift valleys and escarpments can
occur. Compression forces can also produce these features if the
area acted upon consists of resistant brittle rocks. If rocks are soft,
folds are formed.

Earthquakes and volcanoes result from a movement of tectonic
plates as a result of built up of temperature and pressure into the
crust. High temperatures and pressure cause the earth’s crust to be 
 37



always under great tension. When the rocks cannot withstand the
stress, they give way through a fracture and their dislocation produce
shocks. Surface vibrations produce an impact on both physical and
human structures. 

Earthquakes tend to be concentrated in plate margins belts.
Earthquakes are a natural hazard, particularly in densely populated
areas.

The movement of magma into the crust or onto the surface of the
earth is called vulcanicity. Internal features include batholiths, sills,
dykes and laccoliths. External ones comprise of volcanoes, lava
plateaus, hot springs and geysers. Vent eruptions produce ash and
cinder, lava and composite volcanic cones. A volcano can either be
active, extinct, or dormant.

Volcanoes unlike earthquakes have both negative and positive
impacts. Apart from their destructive nature, volcanic soils are in
many cases fertile and excellent for agriculture.


EXERCISES



1. What is the cause of vertical and lateral movements into the
earth’s crust?

2. With examples describe the formation of fold, block, volcanic
mountains and rift valleys. What are the main characteristics of
each?

3. Describe the main intrusive features of volcanism.

4. Explain ways in which the distribution of earthquakes (a) is
similar to that of volcanoes (b) different from that of volcanoes 
 38



5. Explain why earthquakes are formed along all plate margins.
What are their impacts to human beings?

6. Examine the positive and negative impacts of volcanoes to
man?


REFERENCES

Arber, Nicola, Sue Lomas, Garrett Nagle, Linda Thomson and
Paul Thomson (2000); A2 Geography: Heinemann
Educational Publishers, Oxford.
 Bowen, Ann and John Pallister (2001); A2 Geography: Heinemann
Educational Publishers, Oxford.
Bunnett, R.B (1990);  Physical Geography in Diagrams for Africa
(8
th
 edition). Longman Group Ltd. Hong Kong
Clark, Audrey (1990); Geography Dictionary. Geographical
Publishers Ltd London
Bolt, B.A (1988); Earthquakes, W.H.Freeman and Company, New
York










 39
LECTURE FOUR

EXTERNAL GEOMORPHIC PROCESSES
WEATHERING AND MASS MOVEMENT


4.1 INTRODUCTION
In the foregoing lecture we learned about internal processes that give rise to the
formation of various landforms into and onto the surface of the Earth. In this
lecture you will be exposed to processes which take place on the surface. These
processes embrace weathering, mass movement and erosion, which change the
shape of the landforms.

Weathering is the action of the weather on objects exposed to it. The action can
lead to physical, chemical and or disintegration of rock in situ by exposure to
water and the atmosphere. Weathering does not involve transportation of
material. The main physical agents are shattering, frost actions and temperature
change. Plant roots and burrowing animals are organic agents while chemical
processes consist of carbonation, hydration, hydrolysis, oxidation, solution and
corrosion (Clark 1990:354). You shall learn how they take place and the
resulting features later in this lecture.

Denudation which is the wearing away of rocks exposed on the Earth’s surface,
includes the results of both weathering and erosion. Denudation involves
weathering, erosion and transportation.
 TAKE NOTE

In situ refers to the fact that the breakdown of rocks takes place
where the rock is situated without involving any transportation.


 40
OBJECTIVES

After reading lecture four, you should be able to:
(i) Describe the process of weathering, and resultant features 
(ii) Describe the process of various types of mass movements and
resultant features
(iii) Discuss factors that influence weathering and the main types of
weathering,
(iv) Critically analyse the significance of weathering to human
beings and their environment.

4.2 WEATHERING
Weathering refers to the process of weakening, breaking up and finally
disintegration of the rocks which form the surface of the Earth and rocks that
lie exposed to weather. The process is called weathering because the actions
are driven by forces of the weather namely; changes in temperature, frost
action and rain action. Weathering is divided into three main types;
mechanical, chemical and biological.

When weathering takes place, rock changes occur without involving any
movement, whereas erosion (wearing away) takes place only with movement.
Weathering and erosion work together thereby lowering the height of land
surfaces. Weathering speeds up rates of erosion where particles and pieces of
disintegrated or decomposed rock are subjected to the operation of mass
movement down-slope due to gravitational force. Such particles can be
transported to distant places by agents of erosion.

4.2.1 Mechanical Weathering
This process is also called physical weathering. It breaks up the rock without
any change to its exiting mineral structure. Such processes include freeze-thaw
or alternate heating and cooling. It follows that the disintegration of rocks is a
result of pressure release 41
 (a) Temperature Changes  
This is significant in hot and arid environments. The daily changes in
temperature cause rocks to expand during the day and to contract at night. This
causes the outer parts of the rocks to experience internal stresses as the heating
and cooling does not penetrate far below the surface. The stresses in the outer
layer of rocks pull away from the layer beneath. This process is termed
exfoliation. The plates of the rock that peel of and fall to the ground are further
broken into smaller pieces by the force of alternate expansion and contraction.
The remaining rounded structures resulting from this process are called
exfoliation domes. However, with the development of cracks, the stresses can
operate to greater depths.

Figure 4.1: Exfoliation Domes Formed by Mechanical Weathering
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Bunnett, F.B (1990:51)

Exfoliation domes occur mainly in hot deserts such as the Kalahari and Sahara.
Where it happens that the rock is coarse-grained igneous rock, granular
disintegration can also produce dome-shaped structures. When a rock absorbs
water, various minerals expand and contract at different rates and thus granular
fragments drop from the rock. The creation of joints near the surface increases
the vulnerability of the rock to further mechanical weathering.
 42
(b) Frost Action
Most rocks contain cracks and some contain joints. When water enters these
and freezes its volume increases. Ice occupies 9% more volume than an
equivalent mass of water. This exerts great pressure on the sides of the rock
and continued cooling and expanding finally causes the rock to split along the
lines of weakness. With time angular blocks later break into smaller particles.
These drop from the rock and accumulate at the base of the slopes and are
called screens.  The whole process is called block disintegration. Frost action
takes place both in the arctic and cool temperate regions where temperatures
are very low during winter (Bowen, 2001: 100; Bunnett 1990: 52).

Figure 4.2: Block Disintegration
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Bunnett, F.B (1990:52)

(c) Biological  or Organic Weathering 
This consists of both physical and chemical weathering. Micro-organisms such
as bacteria cause both mechanical and chemical break-up of rocks by oxidising
minerals. Plants and animals also increase the carbon dioxide content of the
soil and this increases the weathering potential of the biosphere. On the other
hand, roots of plants and trees, and the work of burrowing animals such as
rabbits, cause rocks to disintegrate physically. 43
4.2.2 Chemical Weathering
This is responsible for the rotting, and decomposition of many types of rocks
on a massive scale. Minerals in the rocks are decomposed by agents such as
water, carbon dioxide and organic acids. Minerals in the rocks vary in their
resistance to chemical agents. Because of this weathering attacks rocks
selectively.

The rate of chemical weathering increases with temperature. For this reason,
the largest rates of chemical weathering take place in the hot, wet tropics.
Similarly, the highest and most rapid rates of vegetation decay and nutrient
recycling is high in hot, wet tropics.  As a consequence of this process, many
organic acids are released by the vegetation on the forest floor thus spreading
up the process of chemical weathering. Outside the tropics the end result of
chemical weathering are sand and clay, which are left, unchanged and thus
remain stable (Bowen, 2001).

In humid tropics, both sand and clay remain unstable and can be removed.
Aluminium and iron are the most stable minerals. That is why tropical soils
have a higher concentration of oxides of aluminium and iron which attributes to
their characteristic yellow–red colour. Chemical weathering consists of five
processes: Solution, hydration, hydrolysis, oxidation and carbonation.

 (a) Solution 
Rocks can be weathered when the salts they contain dissolve in water to form a
solution. Only a few minerals directly dissolve in water. However, some,
particularly Calcium carbonate dissolve freely in water containing Carbon
dioxide. Rainwater dissolves both carbon dioxide and oxygen in the air such
that it reaches the ground as a weak carbonic acid. This is able to turn many
insoluble minerals into soluble minerals that can be carried away in solution.
 44
This kind of weathering is well observed in limestone areas where solution
renders joints to become widened and deepened. Thus grooves called grikes
which are separated by flat-topped ridges, called Clints develop. In humid
tropics so often the majority of minerals dissolve in water with the exception of
iron and aluminium. These accumulate in the top layers of the soil through
leaching thus developing lateric soils.

Figure 4.3: Grikes and Clints
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Bunnett, F.B (1990: )

(b) Hydration 
This happens when certain rock minerals take up water and form new
compounds. For instance haemotite is an iron oxide and when it combines with
water it gives limonite which is another iron compound. Calcium sulphate
absorbs water to form gypsum whereas felspar results into clay.

(c) Oxidation 
This is a process of rock taking up oxygen from the air and then combines with
a mineral. This process is more active in rocks that contain iron. When oxyge 45
combines with the iron it forms iron oxides. The new minerals formed by
oxidation are prone to being attacked by other weathering processes. 

Hydrolysis often precedes and accompanies oxidation. The oxidation of iron
breaks the structure of a rock in which iron and a silicate are joined.
Subsequently, the rock easily breaks.

(d) Carbonation 
This is a chemical process in which rainwater charged with carbon dioxide
forms carbonic acid that reacts and dissolves limestone and other basic oxides.
Hydrogen carbonate ions react with a mineral to give a soluble compound,
which can be carried away in solution. More often, hydrolysis accompanies
carbonation. The two processes break down a felspar into clay, calcium
carbonate into more soluble calcium bicarbonate. 

The last processes of chemical weathering which involves wearing away of
rock or sand by chemical and solvent action are collectively referred to as
corrosion.

4.2.4 Factors Affecting the Type and Rate of Weathering
The main factors that influence weathering are the hardness, jointing and
texture of rocks, relief and climate. The abundance of water, oxygen and
carbon dioxide accounts for the fact that the major chemical weathering
reactions are hydration, oxidation and carbonation.

(a) Rock Resistance 
Rocks vary in their resistance to weathering. The rate of resistance is dependent
on the constituent minerals of the rock and how they are cemented together in
the rocks and the extent to which the minerals have been compressed. The
hardness of the minerals in the rock is measured by Moh’s scale of hardness 46
The scale ranges from 10 (extremely hard) to 1 (very soft), quartz for instance
is classified at 7 and gypsum at 2.

Most igneous rocks are hard due to their mineral constituents such as quartz
and feldspar. When the minerals cooled and crystallised they were tightly
bounded together. In contrast, sedimentary rocks tend to be soft because they
are more often cemented together by soft cement. However, if the cement is
hard, the rock is very resistant to weathering as in the case of rocks cemented
with silica (Lines, et al 1996:60).

(i) The Texture of Rocks (The crystalline state) 
In many cases coarse-grained rocks are likely to weather more rapidly than
fine-grained rocks, which are composed of the same minerals. Usually one
mineral in a rock is weathered more rapidly than others. The weathering of
such a mineral loosens the whole fabric of the portion of the rock exposed to
weathering. 

(ii) Rock Jointing 
This influences the nature and rate of weathering in both mechanical and
chemical weathering because the joints increase the surface area exposed to the
agents of weathering. In limestone areas, chemical weathering concentrates
along joints and bedding planes. The joints allow acidic solution, oxygen and
carbon dioxide to enter the rocks thereby encouraging chemical decomposition.

The pattern of jointing determines the character of the land features produced.
For example plutonic rocks such as granite have a jointing system that divides
the rock into rectangular blocks. When these are chemically weathered they
form piles of semi-rounded boulders. In contrast, basalt has a well-defined
jointing pattern, which forms vertical polygonal columns.

 47
(b) Relief 
This influences mechanical weathering. In order for mechanical weathering to
continue, new rocks need to be exposed. Thus in highland areas, landslides,
slump and solifluction result from the exposure of bare rock. A thick layer of
soil or weathered material overlies none weathered rock, protecting it from
being weathered mechanically.

(c) Climate 
Climatic conditions determine to a large extent the process of weathering. For
example in tropical areas with low rainfall, chemical weathering is more
moderate than in areas with heavy rains where it is stronger. Exfoliation and
granular disintegration are most effective in regions with a large daily range of
temperatures such as in the semi- arid and continental deserts. Cool climate
provide freeze-thaw conditions which allow strong mechanical weathering

 (d) Human Activity 
Now and again human beings intensify processes of weathering through
cultivation, building and construction as well as mining. Also, the introduction
of gases, car emissions and other pollutants into the atmosphere accelerates
chemical weathering.

4.3 MASS MOVEMENT
Mass movement refers to the transfer, sliding, falling, creeping or flowing of
rock materials produced by the agents of denudation (weathering and erosion
down slope) under the influence of gravity. It is a link between weathering and
transport by agents of erosion. The force of gravity acts constantly on all rocks
and debris. While gravity forces loose materials down slope, there is resistance
to movement from friction and cohesion that have to be overcome before any
movement can take place. Water is well known for achieving this since a mass
of rock material, which is well watered, moves easily than a dry mass of rock
material (Bowen, 2001:106 48
Usually mass movement takes place slowly, but sometimes it takes place
suddenly! The rate of movement depends on the steepness of the slope. The
rate of movement of loose material moves down faster over steeper slopes.
Other factors influencing movement include the nature and weight of materials,
and the amount of water in the material. More dense materials tend to move
quickly on a steep slope whereas light materials move slowly. Sudden
movements give rise to landslides. 

4.3.1 Land Slide 
A landslide is the sliding down under force of gravity of a mass of land on a
mountain or hillside. This takes place when large quantities of loosened surface
rocks and soil suddenly slide down a cliff face or valley side. A landslide may
either take the form of sliding or slumping. The latter is common on slopes
made of clay (Clark, 1990:55). 

A number of actions may trigger the occurrence of a landslide. The
undercutting of the base of a steep slope by a river or by the sea and the
steeping of a slope by human activities such as quarrying or clearing up
vegetation from a steep slope. An earthquake or prolonged heavy rains in
mountainous areas such as in the Usambara cause landslides. Buildings and
roads can be buried. When landslides occur in a populated area, loss of life and
property may take place.
 Figure 4.4: Land Slide
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are needed to see this picture.
 49
4.3.2 Soil Creep 
This is the slow downward movement of soil under force of gravity common
on all sloping land. Rainwater enables soil particles slide over each other.
Boulders and stones in the soil, or resting on it, are carried down the slope by
the soil. Other factors, which influence soil creep, include heating and cooling
of soil, alternate wetting and drying of the soil, tramping of grazing animals
and burrowing of animals in the soil. Soil creep can be recognised by fences
and trees that lean down the slope.

4.3.3 Mudflow 
This is a moving mass of soil made fluid by continued heavy rains or melting
snow on a slope. Mudflows can take place on desert slopes that are unprotected
by vegetation cover. Other places where mudflows take place are on the slopes
of an erupting volcano when heavy rains fall on the volcanic ash, in tundra
regions during early summer, when frozen soil thaws and turns into a semi-
liquid state, thus able to slide over the still frozen subsoil (Bunnett, 1990:54). 

4.3.4 Rock Fall 
This is a free fall of individual boulders or blocks of bedrock down any steep
slope due to the force of gravity. 

SUMMARY



In the past weathering was seen as a distinctive process of
landscape formation, today it is placed in the broader context of
landform development and the various types of weathering are
tolerated as simultaneous and interrelated processes. In the analysis
of landscape formation, weathering is seen to contribute to the
formation of rock waste, which is an initial input into the system.
Weathering and surface transport are also regarded as the two main
processes responsible for slope formation. Moreover, the study of
soil formation also starts with rock weathering 50

 When weathering takes place rock changes occur without involving
any movement. The two most important factors influencing
weathering are rock structure and climate. Chemical and physical
weaknesses make a rock susceptible to at least one type of
weathering. Granite is a strong, resistant rock, but its mineral-
felsipar is affected by hydrolysis and breaks down chemically.
Limestone is affected by carbonation. Temperature changes in hot
arid environments cause exfoliation. Chemical weathering is
enhanced by increases in temperature coupled with rainfall. It takes
place by solution, hydration, hydrolysis, oxidation and carbonation.

Generally, the rate of weathering is influenced by the mineral
composition, the texture of rocks, rock jointing, relief and climate.
Human beings also intensify the process of weathering through
cultivation, grazing, building, mining and construction.

Mass movement involves the transfer of large quantities of
weathered material down slope. The movement may be a slow one
as in the case of soil creep or rapid as it happens in landslides. The
four main types of mass movement are soil creep, mudflow,
landslide and rock fall. The latter two are hazardous to human
beings.


EXERCISES


1. With examples discuss the main types of rock weathering.

2. Compare and contrast weathering processes in a hot arid
environment with that in a hot humid environment.

3. Briefly explain the factors which influence the rate of
weathering.
 51

 4. Examine the advantages and disadvantages resulting from rock
weathering
5. Describe the various types of mass movement and name the
resultant features.

REFERENCES
 Bowen, Ann and John Pallister (2001), A2 Geography. Heinemann
Educational Publishers; Oxford.
Arber, Nicola, Sue Lomas, Gerrett Nagle, Linda Thompson and
Paul Thompson, (2000), A2 Geography, Heinemann
Educational Publishers; Oxford. 
Bunnett, R.B (1990), Physical Geography in Diagrams for Africa,
Longman Group; Ltd. Hongkong
Clark, Audrey N. (1990), Dictionary of Geography; Geographical
Publications Ltd, London.
Lennon, J. Barnaby and Paul G: Cleves, (1983), Techniques and
Field Work in Geography. UN Winhyman Ltd. London.
Lines, C; Laurie Bowlwell and Anne Fielding Smith (1996), A
Level Geography. Letts Educational, London










LECTURE FIV 52

EXTERNAL GEOMORPHIC PROCESSES
Erosion and Deposition


5.1 INTRODUCTION
Erosion is the process of the weathering away of the land surface by natural
agents such as running water, ice, wave action, wind and the transportation of
the resultant rock debris (Clark, 1990:107). The process does not involve
weathering of rocks in situ or mass movement. Processes of erosion include
abrasion, corrassion, attrition and plucking. Once weathering breaks down rock
surfaces, the various agents of erosion are able to carry out their work easily.
Water is the main agent of erosion at work in the world (Arber, et al, 2000:32). 

This lecture highlights the various erosion processes carried out by the agents
of erosion, namely, running water, waves, winds and human beings and a
discussion of various features they form. Glacial action is not considered for
here for convenience. However, you are advised to read on how it operates.

OBJECTIVES


After reading this lecture you should be able to:
(i) Discuss the main agents of erosion;

(ii) Describe the process of river action, wind action and wave
action;

(iii) Describe the processes of deposition by various agents and
the resultant landforms;


(iv) Explain the significance of erosion to human beings.


 53
5.2      EROSION AND DEPOSITION BY RUNNING WATER
When it rains, only a small proportion of rainfall reaches the river channel
directly. A large part is held and stored in leaves and branches of plants. This is
called the interception zone. The amount intercepted depends on the type and
density of vegetation as well as rainfall intensity. Rain from heavy rainstorms
saturates soil more easily than gentle drizzle. 

Before rainfall reaches the surface of the earth, some is evaporated into the
atmosphere. The water that reaches the surface moves into the soil and this
process is called infiltration. The soil ability to absorb rainwater is called
infiltration capacity before saturation. The soil has a limit to absorb rainwater.

The water which infiltrates flows by gravity into the soil to the water table. It
may also flow as underground water and finally reach a river channel. Once it
becomes part of a river, flowing water transports and deposits material far
away from their original place. 

The water that exceeds the soil’s infiltration capacity flows on the surface of
the earth as runoff, depending on its volume, slope and nature of the soil.
Runoff erodes soil and at the same time forms small streams that join together
to give larger streams, which subsequently join to form a river. Where streams
join to form a river is called a confluence and the streams are called tributaries.

5.2.1 Erosion by River Action
The amount of material carried by a river depends on steepness and resistance
of the rocks, the amount of water flowing down into it and the material
delivered down the valley slopes. The flow of a river depends on the energy
provided by gravity which is also determined or related to the gradient of its
bed and volume increases. 

There is a relationship between velocity of water in the river channel and the
particle sizes, which can be eroded, transported and deposited. Lower speed 54
allow small particles to be moved on the channel bed while high speed can
carry larger particles. Consequently, the larger the particles the grater the
velocity required to transport them (Lines et al, 1996:70). A river can erode
material through attrition, corrasion, solution and hydraulic action.

(a) Attrition 
Is an action or process by which the load of the river gets broken down when
particles rub against each other. Accordingly, as the load is transported, the
fragments get smaller.

(b) Corrasion 
It is a process of mechanical erosion of a rock surface by the friction of rock
material with the surface. The rock material can be moved under gravity or by
running water (waves, glaciers) or by wind. Corrasion wears away the bed of a
river’s channel, which causes the load to increase.

(c) Solution 
Involves transportation of material which has dissolved in water. It has already
been discussed under chapter four.

Hydraulic Erosion: Refers to the force of moving water that is able to remove
loose material such as gravel, sand and silt. The action is able to weaken solid
rock when it enters into cracks of a rock. Nonetheless, hydraulic action leads to
little erosion if the river has little or no load.

The four processes described above are responsible for the undercutting of a
river’s channel. The erosion is achieved by head ward and vertical erosion,
which deepens its channel. A river's channel is also widened when its sides are
won out by lateral erosion.

5.2.2 Transportation by a River
The load of a river is transported by traction, saltation, and suspension and by
solution. Traction refers to the dragging of large material such as pebbles alon 55
its bed. Saltation is the bouncing of smaller pieces down its bed. Under
suspension, light materials, such as silt and mud are carried in water as the river
flows. Finally those minerals that dissolve in water are transported by solution.
A river transports its load until when it has insufficient energy to transport it
any further. When this condition happens, the river deposits its load.

5.2.3 Factors Which Reduce the Energy of a River
Water in a river flows in two ways. There is lamina (in layers parallel to the
bed) and turbulent flow (in circular form). When a river’s flow is turbulent, its
energy decreases when it overcomes the friction either on its bed or on the
sides. Bends tend to increase friction and give out energy as heat into the
atmosphere. The shape of a river channel also affects the amount of energy a
river possesses for erosion and transportation. A river uses more energy to flow
through a flat, wide channel than through a narrow deep channel. In addition,
energy is lost when the materials transported are in suspension than moving
material along the riverbed.

When the energy of the river is unable to transport its load, it starts to deposit it
starting with coarse material and ending up with fine material. 

5.3 DEPOSITION BY RIVER ACTION
The laying down of material, particularly of debris transported mechanically by
running water, waves and wind is called deposition. It takes place each time the
velocity of a river decreases. Deposition can occur on the insides of meanders
where the gradient decreases, and where there is high evaporation. It also
decreases when a river enters the sea and thus builds a delta.

Deposition is a continuous process, in that the material is constantly being
deposited and then picked up again and transported to another part of the
channel where it is once again deposited. Deposition is by selection. Heavie 56
materials such as boulders and pebbles are deposited first whilst the fine
sediments such as silt are deposited last.

5.4 FEATURES PRODUCED BY A RIVER 
5.4.1 Upper Part
 It is characterised by V-shaped valleys, potholes, interlocking spurs, waterfalls
and rapids. The V-shaped valley is deepened by vertical corration and widened
by weathering and mass wasting. If there is a resistant rock in the course of a
river, vertical corrasion takes place, causes the valley to deepen with very
narrow with vertical banks. Such a valley is called a gorge. When it is large in
size, it is called a canyon.

(a) Pot-holes 
These are holes, more or less circular, worn in rocks by rotating stones in the
bedrock of the channel of an eddying swift stream (Clark, 1990:251). When
these holes develop into larger depressions, they are called plunge pools.

Figure 5.1: Features in the Upper course of a River
QuickTime™ and a
 decompressor
are needed to see this picture.

Interlocking Spur 57
A Waterfall
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Bunnett, F.B (1990:71)

(b) Interlocking Spurs 
A river tends to flow around resistant rocks such that a river takes a winding
course. Prolonged process causes the bends in the river to become more
pronounced since the water on the outside of a bend flows more quickly and
erodes more this side. This finally causes projections of highland called spurs
which appear to be interlocking.

(c)      Waterfalls and Rapids
 A waterfall is either a sudden deep or perpendicular drop of water in the bed of
a river, occurring where the flow of the river is broken by an almost horizontal
bed of hard rock overlying soft rock easily eroded (Clark, 1990.352). If the face
of the rock is steep, horizontal and dips gently down-river then a rapi 58
develops.  One of the largest waterfalls in the world is the Victoria Falls on the
Zambezi.

5.4.2 Features Produced in the Middle Course of a River Valley
In the middle course of a river, lateral corrasion is more active than vertical
corrasion. As a result, the river passage develops an open appearance. When
more tributaries join it, the volume and the load increases. Here, the
interlocking spurs are cut back by lateral corassion to form bluffs and this
widens the valley floor. Deposition begins especially inside of meanders and
river cliffs and slip-off slopes develop on the inside of the banks.

Figure 5.2: Cut Spur and Widened Valley
QuickTime™ and a
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are needed to see this picture.

Source: Bunnett, F.B.(1990: 74)

5.4.3 Features of a Lower Course of a River Valley
Deposition is the main activity in the lower course. Nonetheless, lateral
corrasion continues to cut back the banks while vertical corrasion is almost
over. At this stage, a river contains the maximum of its volume. Since the
gradient decreases, deposition takes place across the width of the valley floor.
The deposition of material on the valley floor sometimes causes the river to
split into several channels such that it becomes a braided river. The deposited
material may also produce a gently sloping surface called flood plain 59
 (a) The Flood Plain 
Is a gently sloping plain of alluvium which covers the valley floor on which the
river flows in a meandering channel. The plain can have marshes and ox-bow
lakes left after the meanders have been cut off. During floods the river
overflows on the banks, depositing fine sediments on the flood plain. The
deposition on the banks build up a ridge-like feature called a levee. 

The meanders still prevail at this stage but no longer reach the sides of the
valley. The Nile flood plain is the best example. 

Figure 5.3: Bluffs, Flood plain, Levee and Ox- bowl lake 
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Bunnett, F.B. (1990: 75)

Rivers that flow above their flood plain are troublesome to settlements such as
the Hwang.Ho, Yangtse –Kian’g and the Mississippi.

 (b) Delta 
This is a low-lying swampy plain at the mouth of a river, which is formed when
a river deposits solid material at its mouth at a rate faster than that of erosion by
tidal and other currents. As the deposits increase the river splits to make new
channels. These distributaries continue to deposit their load 60
 (c) Necessary Conditions for the Formation of a River Delta
• A river must have a large load
• The velocity of a river must be sufficiently low to allow most of its
load to be deposited in the rivers’ mouth.
• The rivers load must be deposited faster than it can be removed by the
action of tides and currents.

TAKE NOTE

River Congo has a large load but no delta because the high velocity
near its mouth enables most of the load to be carried away.

(d) Types of Delta
(i) Arcuate Delta: This is a fan shaped delta with rounded outer margin, the
arc of the fan spreading into the sea. The delta consists of both coarse and fine
sediments. It is also crossed by a number of distributaries such as the delta of
the Nile, and Ganges 

(ii) Bird’s Foot Delta 
Is a delta where relatively narrow borders of sediments, projecting seawards in
pattern of a bird’s foot flank distributaries. It consists of fine material and has a
few long distributaries that are bordered by levees, which stick out from the
shore. The delta develops when the power of the waves and currents are low
for instance, the delta of the Mississippi.








 61
Figure 5.4: Types of Delta

(a) Arcuate Delta ((fan-shaped) e.g. Nile River.  Has many distributaries
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(b) Bidrd’s–Foot Delta e.g. Mississippi River.  Has very few major
distributaries
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 62
(c) Cuspate Delta (tooth-shaped) e.g. Tiber River.  Usually has one major
tributary
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(d) Estuarine delta e.g. Seine River of France.  The river empties in a
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 (iii) Estuarine Delta
 The delta develops in an estuary (tidal mouth of a river) from materials
deposited in the submerged mouth of a river and thus takes the shape of the
estuary. For instance the delta of River Ob in Russia.

5.5 EROSION AND DEPOSITION BY ACTION OF WAVES
The coastline is the margin of the land, and shoreline is where the shore and
water meet. Where sand is deposited on the shore is called a beach. Coastal
lines are constantly being modified by wave erosion.

Wave erosion causes some shore lines to retreat while wave deposition causes
others to advance. Coasts are varied in character. Some costs are high while
others are low. Some are steep, gentle, and rocky while others are sandy. The
nature of a coast results from wave action, tidal currents, and the nature of
climate. Other coastal changes may be caused by human activities (Bunnett,
1990.105).

Figure 5.5: Sea, Shore, Coast and Cliff
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Source: Bunnett, F.B (1990:105)

Waves are formed by blowing wind whose lower layer encounters friction with
the surface of the sea causing the various layers of wind to travel at different
speeds. As the air develops a circular motion causes the surface water to take
the form of a wave. It is not the water that moves but rather the waveform 64
When a wave travels in shallow water its water and its top fall forward,
throwing the water up the beach. This is called a swash. When the swash drains
back down the beach it is termed the backwash. The apex of the wave is the
crest whereas the lower part is the trough. The height and power of a wave
depend on the strength of the wind and the distance of open water on which it
travels. 

Wave action consists of three main actions, corrasion or abrasion, hydraulic
action and attrition. Boulders, pebbles and sand that bounce against the base of
a cliff by breaking waves thereby undercutting and breaking rock cause
abrasion.

The second action is hydraulic action, which is caused by water which is
thrown against a cliff by breaking waves. The water, which enters cracks
causes them to expand and eventually crushing the rocks. Finally we have
attrition. This is the breaking up of boulders and rocks as they are pushed
against the shore and against each other by breaking waves (Bunnet,
1990:107).

5.5.1 Features Produced by Wave Erosion
These include a cliff, caves, geos, arches and stacks.
A cliff is a high steep or perpendicular face of rock produced by wave erosion.
The cliff continues to sharpen as its base is attacked by wave action. Finally the
upper part of a cliff may collapse providing the waves with material for further
erosion. Resistant rocks form headlands while non-resistant ones form bays.





 65
Figure 5.6: Overhanging cliff, Cave, Blow hole and Geo
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Source: Bunnett, F.B (1990:108)

A cave is a tunnel like opening at the base of a cliff face developed along a line
of weakness through continued wave erosion. If a passage from the cave opens
upwards to reach the top of the cliff it produces a blow-hole. Eventually th 66
roof of a cave collapses and a long narrow inlet called geo, form. When a cave
in a headland is eroded it forms an arch and when this collapses, the end of the
headland stands up as a stack.

5.5.2 Features Produced by Wave Deposition
Depositional features created by sea waves include beaches, spit, tombolo and
mud fall.

Figure 5.7:  Headland, Bay, Arch and Stack 
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Source: Bunnett, F.B (1990:109)

(a) A beach is the accumulation of loose unconsolidated material on the
shore of the sea at or near the limits of wave action, normally between the low
water tide line and the highest point reached by storm waves at high tide
(Clark, 1990:33). Waves can deposit material in a bay to form bay-head
beaches. These beaches do not extend to the headlands where erosion is
dominant.

 (b) A Barrier beach is a ridge of sand that is parallel to the coast
The beach develops from an under water offshore bar. It is a large narrow
beach   which has been formed by materials deposited on it. The material is
gradually carried along the shore by the swash and backwash movement whic 67
together result in long shore drift. Therefore beaches are constantly undergoing
changes.

(c)    A spit is a narrow ridge of sand and pebbles resulting from long shore
drift, attached to the seashore at one end, extending some distance seaward,
terminating in the open water at the other (Clark, 1990:302). A spit is formed
by deposition of material by long shore drift. If the waves meet the coast
obliquely, the end of the spit is curved or hooked such as that in Walvis Bay,
Namibia.

(d) A Bar is described by Bunnett (1990) as a ridge of sand material that
lies parallel or almost parallel to the coast unattached to the coastland. When it
lies across a bay it is called a bay-bar. However if the bar joins an island to the
mainland it is called a tombolo. A long tombolo occurs near Las Hafun in N.
East Somalia.

Finally is large expanse of fine clay or silt deposited along gully sloping coasts
and particularly in bays. At Such characteristic is called a mudflat. At high tide
such areas may be covered by water and or colonised by vegetation such as
mangroves. 










 68
Figure 5.8:  Bar Spit and Tombolo
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5.6 EROSION AND DEPOSITION BY WIND ACTION
Wind action is important in arid and semi arid regions due to absence or little
vegetation cover. Most of the arid regions lie in the trade wind belt where the
dry winds blow offshore between 15-30° N and 15-30° S. Major deserts
include the Sahara, Arabian, Iranian, Thar, the Kalahari, the Namib, Great
Australian desert and the Atacama deserts. 






 69
Figure 5.9: Rock Pedestal, Zeugens and Yardangs


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Source: Bunnett, F.B (1990:86)

A rock
pedesta 70
Transport and deposition are the most significant processes of wind erosion.
Wind blows away fine particles over long distances while the coarser particles
bounce over the surface. The bouncing movement is called saltation. Similar to
other agents, wind erosion takes place in various ways as given below:

5.6.1   Abrassion 
This is the process of wearing down or wearing away by friction. The process
involves gradual reduction in the size of pebbles as one rubs against another or
bounces against rock surfaces.

5.6.2    Deflation
Is the removal of fine rock debris by wind in arid and semi arid landscapes
(Clark1990: 82. The process is responsible for the lowering of desert surfaces
to produce depressions.

5.6.3   Attrition 
This is the wearing away of rock particles as they rub against each other when
they are transported by wind.

5.6.4     Features Produced by Wind Erosion
Wind abrasion affects rock masses and wears them down to form new features
as described below.

(a) Rock Pedestals
These are tower like structures formed by the wearing away of softer layers by
wind abrasion. They are commonly seen in the Tibest Mountains in the Sahara
desert.



 71
Figure 5.10:  Major Hot and Temperate Deserts of the World
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Source: Bunnett, F.B (1990:88, 89)

 (b) Zeugens
These are ridge like structures which develop by wind abrasion in dessert
landscape comprising layers of hard rock underlain by a large layer of soft
rocks. The resistant rock form zeugens while the weak rocks form furrows.
Wind abrasion lowers the zeugens and widens the furrows. 

 (c)       Deflation Hollows 
These are hollows formed by continued deflation in desert landscapes.
Sometimes these hollows reach down to the water bearing rocks. Where a
swamp or an oasis develops. For example, the Quatara depression South West
of Alexandria in Egypt was formed that way. A depression can be initially
formed by faulting and then deepened by deflation.

(d) Inselbergs  
These are isolated pieces of round topped masses of rock left standing after the
removal of the original surface by wind erosion. Some of them are remains of
Plateau edges, which have been cut back by the removal of the weathered
debris by sheet wash. Others may be a result of a combination of wind and
water erosio 72
5.6.5     Features Produced by Wind Deposition
Depositional features are mainly formed by sand or desert dust. As winds blow,
they transport sand and dust from one place to another. The main features of
wind deposition are sand dunes. These vary in size and shape.

(a) Berchans Dunes 
Berchans Dunes are crescent shaped and lie at right angles to the prevailing
winds with the horns pointing in the direction to, which the wind blows.
Usually such features form when there is an obstruction such as a big rock or
vegetation in the path of the wind. The sand accumulates behind the obstacle to
form a mound. As the mound grows larger, its two edges are elongated
downwind thereby forming the crescent shape.

Figure 5.11: Barchans and Seif Dunes
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Source: Bunnett, F.B (1990:91)

The windward side of the dune is gently sloping while the leeward side is steep
and slightly concave. Barchans occur in groups and they can be seen near the
Futa Djalon plateau in Northern Nigeria and in the Namib Desert 73
 (b) Seifs
These are ridge shaped sand dunes with steep sides lying parallel to each other.
Seifs have very sharp crests and are separated by flat areas. A seif usually
develops from a small sand ridge, and as it forms, it slowly moves forward in
the direction of the prevailing wind. Examples of seifs are observable in the
Namib Desert between Walvis Bay and Luderitc. 

Very fine particles are blown beyond the desert margins and are deposited to
form loess. Extensive loess deposits are found in northern China originating
from Gobi desert.

A combination of wind and water action in desert landscape produces sandy,
stony, and rocky desert landscape types.

Stony desert or Erg: consists of undulating plain of sand whose surface is
blown into ripples and sand dunes. An example is the sand Sea of Egypt.

Rocky desert or Reg: is characterised by boulders, angular pebbles and gravels
produced mainly by weathering.

Rock desert or Hamada: is a desert landscape consisting of bare rocks from
which all fine materials have been removed by deflation.  Abrasion polishes
and smoothens the rock surfaces.

SUMMARY


Erosional and depositional processes are largely responsible for
the continuous shaping of the earth’s surface. Running water,
waves and wind are the main agents of erosion in the tropics.
Glacial erosion is prevalent in temperate lands.

The erosive power of a river depends on its volume and the
gradient of its bed. Generally the volume of water increase from a
rivers’ source to its mouth but the gradient decreases from the
source to the mouth. When the energy of the flowing rive 74



slackens, some of its load is deposited. Water falls; rapids, the
flood plain, meanders and deltas are some of the outstanding
features produced by a river.

Further more, sea waves have great erosive power and are
responsible for the shaping of coastlines. Wave erosion produces
cliffs, arches and stacks depending on the resistance of rocks being
acted upon.

Where the energy of waves drops, the material transported by way
of coastal drift are deposited and may build up either sand
beaches, spits, sandbars, a tombolo or a mud flat.

Wind transport and deposition are the main agents of denudation
in deserts and together they produce features such as barchans and
seifs. Wind transports materials mainly by saltation. Wind erosion
is responsible for the formation of rock pedestals, zungens,
inselbergs and deflation hollows. Its erosive activity is mainly that
of abrasion. Wind erosion and deposition are active in arid and
semi arid landscapes.

EXERCISES


1. Visit a nearby river and examine ways by which a river
erodes material.

2. The energy of the river determines its erosive power: What
factors account for the energy of a river?

3. Describe the formation of various features of river erosion
and deposition.

4. (a) Provide a brief description of how waves erode and
deposit material.

 (b) Visit a sea shore and observe its erosive activity. Record
features you see.
 75




5. Describe with the aid of diagrams the formation of a cliff,
stack, arch and bay

6. Describe wind action and the features it produces.

7. With the aid of diagrams provide a brief description of how
the various features of wind erosion and deposition are
formed.



REFERENCES


Arber, Nicola, Sue Lomas, Gerrett Nagle, Linda Thompson and
Paul Thompson, (2000); Heinemann Educational Publishers;
Oxford. 
Bunnett, R.B (1990);  Physical Geography in Diagrams for Africa
(8
th
 edition). Longman Group Ltd. Hong Kong
Clark, Audrey (1990); Geography Dictionary. Geographical
Publishers Ltd.
Lines, C; Laurie Bowlwell and Anne Fielding Smith (1996); A
Level Geography. Letts Educational, London.







 76

LECTURE SIX

THE STUDY OF SOIL

6.1 INTRODUCTION
Soil can be defined as the loose surface of the earth. To the common farmer it
is the medium in which crops grow, although, with advanced technology it is
now possible to grow crops in liquid mediums other than soil. Soil may also be
defined as a mixture of mineral and organic matter, water and air. Broadly, soil
can be defined in its evolutionary nature as a natural body of the earths’ surface
having properties due to the integrated effect of climate, and living matter,
acting upon parent material as conditioned by relief over periods of time.

Proportions of the components of soil vary from time to time and from one
place to the other. Soils form over periods of time at different rates and
eventually develop features of maturity. For this reason, we have young and old
soils. The nature of the soil is strongly influenced over time by climate, human
beings, organisms and vegetation.

Soil is very important as a natural resource. It is a medium for plant growth,
land for agricultural use or food production. Soil is also a boundary between
the atmosphere and the lithosphere. The soil collects and purifies water, and
disposes of wastes. However, soil itself can be a pollutant as dust in the air and
as sediments in waters.
 In this lecture, you will learn about factors which influence soil formation. You
will also study the characteristics of soil, and how it can be degraded. Finally,
you will gain knowledge of various methods of soil conservation 77
Soil is a function of the parent material, climate, organic matter, relief and
time. The nature of parent material has a marked effect on young soils.
However, its influence becomes less as the soil becomes older. Climate is of
major importance in soil formation as it determines the type and rate of rock
weathering. Organic life, rainfall, temperature and their variations affect soil.
Organisms such as bacteria and earthworms have a marked effect on soil
formation of organic material. Vegetation despite of being influenced by
climate it supplies organic material and influences microclimates too.
Therefore, if vegetation is altered or interrupted, the microclimate changes
simultaneously.

OBJECTIVES
 After reading this lecture you should be able to:
(i)  Define and describe the main constituents of soil;
(ii) Describe the properties of soil colour, texture and structure;
(iii) Discuss the factors for soil formation;
(iv) Identify and explain soil horizons with focus on level of
consolidation;

(v) Explain factors which influence soil fertility;
(vi) Describe the various methods of soil conservation.

6.2 SOIL PROFILE
The soils on the earth’s surface are always undergoing continual change. This
phenomenon is clearly understood by observing a vertical section of a series of
layers or horizons of the soil surface. Growth of plants results in the
accumulation of some organic residues. These plus animal remains form the
organic part of the soil. 

 78
Figure 6.1:  A soil Profile
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When the surface layer of the soil attains a thickness and a darkened colour due
to accumulation of organic matter an ‘A’ horizon is formed. Below it is the B-
horizon where colloidal particles accumulate through percolation. Such
colloids include clay, organic matter and oxides of iron and aluminium. Below
the B-horizon is found the C-horizon composed of the parent un-weathered
rock. The three horizons form what we call a soil profile. The horizons are
characterized by differences in colour, composition and texture. While the
upper part of the soil profile is rich in organic matter, the lower soil horizons,
contains more stones due to proximity to the bedrock 79
6.3 CONSTITUENTS OF SOIL
6.3.1 Mineral Soil 
About 98% of the earths crust is composed of 8 chemical elements. Among
them oxygen and silicon comprise 75% of it while others occur in small
quantities (Young 1989). We should bear in mind that these elements and their
compounds are not evenly distributed. Weathering of rocks results in the
destruction of existing minerals and synthesis of new minerals. In this way,
clay minerals are formed and nutrients are made available for plants. Even life
in the seas awaits nutrients released by weathering on the land and carried to
sea by rivers. Consequently, all life on earth depends largely on the minerals
and weathering processes.  

As soil ages it looses most of its original minerals. In the early stages of
weathering soils are dominated by gypsum and are considered as young soils.
These are common in semi arid regions where chemical weathering is restricted
by limited water. Soils that are in the intermediate stage often contain quartz in
the fine silt and clay fractions. These are common in temperate regions and
develop under grass or trees. They include the major soils of the wheat and
corn belts of the world.

?


Which are the major whet belts of the Worlds?

Soils in advanced stage of weathering are dominated by kaolinite and limonite.
They have lost most of all the original minerals of the parent material
weathering. These soils are characterised by extreme infertility. Most of the
nutrients circulate through the vegetation and they are mainly found in the
humid tropics.

6.3.2 Soil Water 
Soil water is held as thin water films around soil particles and micro pores. It
can be acidic, alkaline or neutral. Soil water content varies from day to da 80
with weather changes. It also changes from place to place and from one soil
type to another depending on their position in the soil profile and water
availability. 

Soil water as a source of life provides plants with moisture and acts as a
medium of transport for nutrients. Soils deficient in soil water are agriculturally
poor since crops cannot obtain sufficient moisture and consequently die out.
This is paramount particularly, in dry sub humid and semi arid environments,
where availability of soil water frequently limits plant growth (Young,
1989:232). Nonetheless, too much water in soils is unsuitable for plant growth
due to water logging. Water logged soils are poor because they have only few
pores that can be occupied by air. Many micro-organisms that are essential for
nutrient cycling live on oxygen and therefore, cannot survive in waterlogged
soils. 

6.3.3 Soil Air 
Soil air is usually saturated with water vapour and rich in carbon dioxide. The
amount of air in the soil depends on the availability of pores, which in turn are
determined by the texture of the soil. Air enables micro-organisms to act.

6.3.4  Soil Organic Matter 
When plants die and left out to rot bacteria act on them to decay. The organic
material present in the soil consists of two parts; plant remains and fully
decomposed organic matter; the humus (Ibid, :108). The nutrients of the
decomposed dead plants are returned onto the ground. Organic matter is
essential for enriching the soil. However, high concentrations of organic matter
do not always correspond with highly fertile soils.

Concentration of organic matter in the soil varies considerably. Leafy plants
supply large amounts of organic matter whereas root crops supply very little.
Environmental conditions determine the nature of population of microbes
present at any given time in the soil. Generally, the fertile, fine textured soil 81
high in organic matter contain many more microbes than the coarse-textured
soils which are low in organic matter. The actual volume of organic matter
depends largely on the balance between the rate of gain and the rate of loss of
matter. Drained, aerated soils allow a more rapid breakdown of dead vegetation
and a more speedy return of nutrients to the soil than poorly drained soils. 

Soil organic matter is important in maintaining soil fertility because it
maintains soil physical conditions, such as water-holding capacity, and
provides a balanced supply of nutrients. The soil is in addition, protected
against leaching until released by mineralization. 

6.4 SOIL PHYSICAL CHARACTERISTICS
6.4.1 Texture 
Soil texture refers to the size of the particles that make up the soil. The three
broad categories of soil are sands, loams and clays. Sand soils are light, well
aerated and well drained and composed of fairly coarse material or grains. In
contrast, clay soils are sticky and poorly aerated. They mainly consist of fine
particles and are usually water logged. Loamy soils are a combination of sandy
and clay soils. This type of soil makes up excellent agricultural soils, because it
is both well drained and fertile. Intermediate soils include sandy loams and clay
loams (Lenon and Cleves, 1983:37).

6.4.2 Temperature 
Soil temperature is important for the germination of seeds and plants. Below
certain critical temperatures, germination and growth will not take place. Corn
seeds for example begin to germinate once the soil temperature rises above 7-
10° Celsius and reaches optimum growth around 35° C.

Soils are heated by insolation.  Different soils heat up and conduct warmth
more rapidly than others. Water content is the most important single
characteristic which controls the rate at which a soil heats up. Because of this 82
removal of excess water from a soil will facilitate changes in soil temperature.
The use of mulches and various shedding devices, also controls soil
temperature. Mulches limit the amount of solar radiation absorbed by the soil
and loss of heat energy from the soil by radiation. In addition, infiltration of
water and loss of water by evaporation can be altered. 

In regions where summers are cool reduced soil temperature, cause reduction in
crop yields. As such, black plastic mulching is used to absorb solar radiation
and reduce heat loss from the soil by radiation and at the same time reduce
evaporation of water from the surface. The net effect of this practice is to
increase soil temperature and hence increase crop yields, although it is costly.

6.4.3 Soil pH 
The pH value of a soil is a measure of the concentration of hydrogen ions in the
soil water. Usually soils of humid regions are acidic and soils of arid regions
are alkaline. In acid soils, the soil solution contains more hydrogen ions (H+)
than hydroxyl ions (OH-) and vice versa in alkaline soils. In most soils pH
values lie between 5 and 9. A pH value of less than 7 is acidic whereas that
greater than 7 is alkaline. A pH of 7 is neutral.

The significance of pH value of the soil does not directly affect crop growth
except in cases of extreme acidity or alkalinity. The major effects of soil pH are
biological. Some organisms have small tolerance to variations in pH others
have a wide range. The pH affects the availability of nutrients for plant growth.
In alkaline soils some nutrients essential for crop health such as iron and
magnesium become scarce at pH values of 7.5 and above.  On the other side, in
acid soils below pH 5.0, the over abundance of nutrients such as aluminium
and iron, mobilised by the acid, may prove toxins to crops (Lenon et al., 1983). 

6.4.4 Soil Fertility 
Soil fertility is the capacity of soil to provide an optimum growth of plants, on
a sustained basis, under given conditions of climate and other relevan 83
properties of land (Lines et al., 1996 :110). Usually fertile soils maintain high
yields and infertile soils lead to low yields. Low crop yields can be due to low
soil fertility, caused by natural soil conditions, or decline in soil fertility by past
unsustainable agricultural practices. Fertile soils are generally associated with:

• deep and well-aerated rooting zone
• availability of organic matter
• suitable conditions for organic decomposition and the incorporation of
organic matter in the soil
•  appropriate soil chemicals 
• optimum levels of soil acidity and alkalinity (pH).

6.5   SOIL EROSION, SOIL CONSERVATION AND SUSTAINABILITY
6.5.1 Soil Erosion 
In lecture five you learnt about various ways by which soil erosion takes place.
Before pointing out what can be done in prevention and repair of soil due to
erosion one should understand the main types of erosion and their
consequences to humankind. Soil erosion happens when land is exposed to the
action of wind and rain. The main types of erosion are:

• Sheet erosion, which is more or less uniform erosion of the whole surface of
a field. The roots of plants, tree roots and poles are increasingly exposed.

• Rill erosion is the development of small natural depressions caused by
surface run-off. While normal cultivation often hides the damage, much
fertile soil is still lost.

• The third type of soil erosion is gully erosion. It causes deep fissures in
cultivable land. If left unchecked, gullies eat their way gradually back into
the hill.
 84
• Finally we have stream bank erosion that converts deep, fast flowing streams
into wide and sluggish meandering watercourses with extensive mud banks.
It can cause serious loss of cultivable land.

Soil erosion occurs when farming practices in use fail to take account of the
ease with which soils can be washed or blown away. Examples of such
practices are; overstocking and overgrazing, shifting cultivation over short
fallow periods, deep ploughing for 2-3 times in a year, crop rotation and
planting wrong crops in the wrong place. 

The consequences of erosion to mankind are severe and many. Foremost, land
is left bare and unproductive, silting reduce fish catch in shallow rivers, and
reservoir lifetime of hydroelectric plant. Gully erosion on the other hand, eats
into cropland, while mud banks reduce navigability of a river, crops are grown
on large unprotected fields, badly managed pasture suffers from wind erosion
and frequently flooded villages become deserted. When land cannot support
people, the poor people migrate to cities giving rise to slums. 

6.5.2 Soil Conservation 
Soil conservation has more often been interpreted to stand for soil erosion
control. However it has a wider meaning. Soil conservation, includes both
control of erosion and maintenance of fertility. This requires, maintenance of
organic matter, soil physical properties, nutrients and avoidance of toxicities in
the soil and its surroundings. A broader field is that of soil and water
conservation, since reduction of water through run off is an integral part of soil
conservation (Young, 1989:10). 

As one goes around in Tanzania some sections of the country show signs of
soil mismanagement. Some farms have been depleted in organic matter content
as revealed by a lighter colour and lower productivity compared to the
surrounding soil. To improve depleted soils, use of improved methods o 85
managing the soils such as application of manure and sustainable land use
including crop rotation is important. This is very essential especially in African
countries where food insecurity is predominant. 

6.5.4  Prevention and Repair (control of soil erosion)
Human intervention is always necessary in order to enhance soil erosion
control. Techniques to accomplish it are biological and physical. Biological
ones involve a fundamental assessment of the suitability of land and the
techniques used to farm it. Physical techniques include many forms of
terracing, methods of gully control, dams for controlling flood and siltation,
and over all water shed management.

 (a)   Biological Methods
• Assess growing conditions and choose the right crop
• Use proper crop management such as strip cropping, crop rotation
• Apply plantation crop combinations for example agricultural crops with
multipurpose trees
• Alley cropping and barrier hedges
• Trees on erosional control structures 
• Windbreaks and shelters are a proven potential to prevent wind erosion
• Sylvopastral practices i.e. inclusion of trees and shrubs as part of overall
pasture improvement
• Reclamation forestry leading to multiple use
 (b)  Physical Methods
• Storm water or diversion drains
• Ridges and bunds
• Grass and bunds and Grass water ways
• Bench terraces
• Platform, orchard terraces.
 86
The importance of soil conservation is summarized by FAO; (2000:2) in the
following words:
“A nation without soil is bankrupt but a nation with appropriate land use
patterns and farming techniques, where erosion has been controlled and
contained, is poised on the springboard of development.’’ All countries should
strive to prevent its soils from being eroded.

SUMMARY



Soil is a function of the parent material, climate, organic matter,
relief and time. Proportions of the components of soil vary from
time to time and from place to place. The proportions are a result
of integrated effects of climate and living matter acting upon the
parent rock. 

The volumes of soil water and soil air are inversely related. As
water enters into the soil, air is freed. Soil water is important for
agriculture, as it is the medium through which nutrients are
transported. Nonetheless too much or too little of it is not suitable
for agriculture.

Time affects the quality of a soil. As a soil grows old it looses
most of its original minerals. In order to maintain its fertility, new
minerals should be added to the soil according to crop
requirements. These minerals are applied in form of chemical
fertilizers, farmyard manure or sound methods of soil
conservation. 

The degree of soil acidity and alkalinity is also important to plants
since some nutrients become less available to plants at the
extremes of pH values. In tropical areas leaching of silica is very
heavy. Leached soils tend to be infertile due to inadequacy of
humus. To sustain crop production, sustainable soil management
is indispensable 87


EXERCISES


1. Define and describe the main constituents of soil
2. Go to the field and observe properties of soil colour, texture
and structure.
3.   Critically, discuss factors for soil formation
4.   Explain the importance of various constituents of soil
5.  Discuss factors which influence soil fertility
 6.  Give an analysis of the various methods of soil conservation

REFERENCES



Lennon, J. Barnaby and Paul G: Cleves, (1983); Techniques and
Field Work in Geography. UN Winhyman Ltd. London.
Lines, C; Laurie Bolwell and Anne Fielding Smith (1996); A Level
Geography. Letts Educational, London
Young, A (1989); Agro Forestry for Soil Conservation. CAB
International, Wallingford.










 88










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 89



SECTION TWO 

HUMAN GEOGRAPHY

Lecture Seven: Constituents of Human Geography
Lecture Eight: Population and Development
Lecture Nine: Agriculture
Lecture Ten: Exploitation of Natural Resources
Lecture Eleven: Application of Statistical Data in Geography
Lecture Twelve: Graphical Representation of Geographical Data
Lecture Thirteen: Topographical Map Interpretation





 90










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 91
LECTURE SEVEN

CONSTITUENTS OF HUMAN GEOGRAPHY

7.1 INTRODUCTION
In Lecture two we defined geography as the description of the earth. This
definition obscures human activities particularly by considering the natural
environment alone. Apart from physical geography, which mainly deals with
the physical phenomena, geography also deals with human phenomena on the
surface of the earth. Fellman et al., (1999:4) underscore geography as the
relationships between human activities and the natural environment which they
occupy and change. Geography also links physical phenomena and human
activities in one location of the earth with other areas.

Apart from natural processes such as volcanic activity and earthquakes, much
of what is observed on the surface of the earth is a product of human activities.
In their struggle for development humans use natural resources to improve their
well-being. In this process, depending on their level of technology they may
improve or degrade the resources. Therefore humans are capable of shaping
their life and the appearance of the earth. This section examines those aspects
of geography which are created by human activities.

 OBJECTIVES
After reading this lecture you should be able to:
(i) Describe the main constituents of human geography
(ii) Explain the relationship between the level of technology of a
society and its level of development;
(iii) Discuss the role of innovation and diffusion in changing the
way people live and behave;
(iv) Explain the importance of harmonising human activities with
environmental characteristics for sustained development
 92
7.2 MAIN CONCERNS OF HUMAN GEOGRAPHY
Human geography puts emphasis on people. It examines where people live,
how they interact over space and the kinds of landscapes of human use they
erect on the natural landscapes they occupy. It is also concerned with
agriculture, politics, cartography, transportation and the economy. In this way,
it integrates with other social sciences and draws on other social sciences as
well.

Figure 7.1:  The Branches of Human Geography and Related Fields
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Fellman, et al., (1999:5) 

The main significance of human geography is that it:
• Helps us to understand the world we occupy and to appreciate the
circumstances that affect people and countries other than our selves
• Clarifies the contrasts in societies, cultures and human landscapes in various
regions of the eart 93
• Provides models and explanations of how things are interrelated in space
thereby providing us a clearer understanding of the economic, social and
political systems within which we live and procure livelihood
• Enables us to be better informed citizens and better prepared to contribute
solutions to societal problems
• Makes us more aware of the realities and prospects of our society in a
changing world
• Opens the way to rewarding and diversified careers as professional
geographers.

The above benefits are possible if people interact. People in spatial interaction
are the starting point of human geographic study. The way people interrelate
depends on their culture. This can be defined as the specialised behavioural
patterns, understanding, adaptations and social systems that summarise a group
of peoples learned way of life (Fellman, 1999:34). Culture is responsible for
the creation of its own cultural landscape and hence the root of regional
differences. 

Farming patterns, language, political organisation and ways of earning a living
are part of the spatial diversity of human geography. The persistence of
differences from place to place makes human geography to address the
question. Why are cultures varied? Fellman and others find the answer to this
question in the way separate human groups developed techniques to solve
regionally varied problems of securing food, clothing, and shelter. In the
process distinct behaviours and attitudes were developed. Due to this, a set of
culture regions showing related cultural complexities and landscapes may be
grouped to form a culture realm or territory. 

7.3 PEOPLE AND ENVIRONMENT
People interact among themselves and with the environment. The environment
in which they interact partly contributes to differences among people. In les 94
developed societies, the acquisition of food, shelter and clothing depends on
the use of natural resources available. In more developed societies
environmental determinism has been overcome. The interrelationship of people
to their environment, their perceptions and its utilization and their impact on it
constitute a cultural ecology. A cultural ecology is the study of the relationship
between a culture group and the natural environment it occupies.

TAKE NOTE

Environmental factors alone cannot account for the cultural
variations that occur around the world. The environment only
places certain limitations on the human use of territory depending
on technologies, national aspirations and existing  linkages with
the larger world.

Since environmental determinism does not fully explain the development of
culture today a viewpoint of possibilism has attracted the  attention of many
scholars. This view holds that the dynamic forces of cultural development are
the needs, traditions and the level of technology of a culture. These affect how
that culture assesses the possibilities of an area and shape choices the culture
makes regarding them (Fellmann et al., 1999:37). Close examination reveals
that each society uses natural resources in accordance with its circumstances.
Changes in a group’s technical abilities or objectives bring about changes in its
perceptions of the usefulness of the land resources. The perception of
environmental opportunities seems to increase directly with economic growth
and cultural development.

Notwithstanding the foregoing argument, the distribution of human population
suggests some environmental limitations on the use of land in certain locations.
For instance, the majority of world’s population is concentrated on less than
half of the earth’s land surface, mainly in the northern hemisphere (ibid).
Densely populated areas are those with relatively mild climates that offer fres 95
water, fertile soil and abundant mineral resources. This reflects partly, the
different potentials of the land under earlier technologies to support population.
Sparsely populated areas include Polar Regions, very high rugged mountains,
deserts and some hot, humid lowlands.

If people recognise or find resources for feeding, clothing and housing, they are
normally attracted to occupy the territory. Recent exploration of Tanzanite in
Mererani-Arusha and opening up of goldfields in Kahama, and Bulyanhulu in
Tanzania have attracted many people into those areas today than before.

7.3.1 Human Impacts on the Environment
The reactions of people to the physical environment have an impact on that
environment. By using it, we modify it, for instance by starting farms, building
roads and cities, thereby creating a cultural landscape, which is  the modified
earth’s surface by human actions.

While human actions can be constructive, they can as well be destructive. For
example, people have hunted elephants and reduced them to small numbers.
Other animal and plant species have become extinct due to overexploitation.
Bad methods of farming have rendered formerly productive regions sterile, for
example parts of Ismani, Kondoa, and Shinyanga, in Tanzania.  This brings us
to the focus on resource management

Sustainable development is development which is continuous. It requires a
long-term accommodation between human actions and environmental
circumstances. When that accommodation is upset either through poor
management of resources by an exploiting culture or through natural
environmental alteration unrelated to human actions, such as the catastrophic
drought the society fails to use it and development of the region become
unsustainable. Former patterns are disrupted. Spontaneous changes in the
environment may also bring down the works of organised society 96
The incidences pointed out above, show that human geography is not static. It
is always undergoing changes. Some changes are minor while others are major
and persistent. For instance, the increasing employment of women in waged
activities has taken place slowly and could be regarded as a minor achievement
when compared with the impact of industrial revolution with its accompanied
urbanisation on societies. Most of the changes are a result of innovation and
diffusion of innovation.

Innovation implies changes to a culture that result from ideas created within the
social group itself and adopted by the culture. It may be the improvement of
technology or simply changes in the social structure. These changes spread
through spatial diffusion. This is a process by which an idea or innovation is
transmitted from one individual or group to another across space. The process
of diffusion of an idea takes place when people move to another area and take
the innovation with them such as seeds or religion. The information about an
innovation also spread through mass media advertising such as the use of
handy cell phone and television sets. Industrialisation is the best example of
diffusion of innovation. It originated in Western Europe and was spread to the
rest of the world. When an innovation remains and spreads from one place to
others then diffusion has taken place. 

In many cases  ideas spread internationally from bigger cities to smaller towns
and down to rural areas, or from prominent people to less prominent ones. This
is termed hierarchical diffusion. There is also, relocation diffusion in which
migrants physically carry the innovation or idea to new areas. For example the
Maasai men plait hair of Tanzanian women in urban areas in Maasai style. 

What we notice here is continuous spread of innovations from their point of
origin and their integration into the structure of the receiving society such that
today societies have no pure culture. Indeed, close observation shows that a big
proportion of what forms a society culture comes from outside. Reflecting o 97
this, a cultural landscape is constantly undergoing changes and this affects the
way people organise space and hence their impact on the environment. The
following lectures examine characteristics of human population and how men
and women exploit natural resources in order to meet basic needs such as food,
clothing, shelter and leisure.

SUMMARY

Human geography puts more emphasis on people, and how they
organise space to procure livelihood. It is also concerned with how
people organise themselves politically and the impacts of such
activities. It provides explanations of how things are interrelated in
space and enables them to be well informed and hence prepared to
contribute solutions to societal problems.

The basis of human success in many activities is interaction. The
way people interact is determined by their culture, particularly
their level of technology. Variation in technology among societies
is responsible for the spatial differences we observe. In less
developed societies, basic needs are largely procured from nature.
The environment determines people’s life. In contrast, developed
societies use their improved technology to control the environment
in the process of procuring livelihood. Due to this, Landscapes and
peoples’ characteristics change through time as human societies
interact with their environment and adopt new innovations from
outside.

EXERCISES 


1. Analyse the main differences between physical and human
geography
2. To what extent does the level of technology of a culture
determine a society’s path towards development 98



3. Discuss the role played by innovation and diffusion in altering
the cultural structure in which you are a participant from that
experienced by your great grand parents
4. Why is adjustment of human activities and environmental
characteristics important for sustained development?


REFERENCES



Fellman J.D Arthur Getis and Judith Getis, (1998); Human
Geography: Landscapes of Human Activities, 6th edition.
The MacGrave Hill Companies, Inc.












 99
LECTURE EIGHT
POPULATION AND DEVELOPMENT
8.1 INTRODUCTION
Population in this lecture is defined as the total number or a specified number
of people in an area at a particular time. Population at a particular time is the
function of births, deaths and migration (fertility, mortality and migration). The
three determinants of population are also referred to as population dynamics.
Population is a resource that requires sound management just like any other
resource if it has to positively contribute to socio-economic development

The size, characteristics, growth and trend of today’s population shapes the
well being of the future population. The number of people, patterns and trends
in their fertility and mortality and rate of growth all affect and are affected by
the social, political and economic organisation of a society. Through these, we
come to understand how the people in a given area live, how they interact
among themselves and with the environment and the pressure they exert on the
land resources. The study of population characteristics is therefore crucial to
the understanding of societal organisation and its needs. This is the main
interest of population Geography. 

In this lecture you will learn about various definitions of population terms, the
main characteristics of population, population controls, and determinants of
population distribution.

OBJECTIVES
After reading this lecture you should be able to:
(i) Define population terms and explain factors influencing
population growth, distribution and density;
(ii) Relate concepts of overpopulation and under population to
resources endowment and level of technology 100


(iii) Use population statistics to explain population structure in
respect to age problems;
(iv) Discuss the impact of fertility, mortality and migration on
socio economic growth;
(v) Discuss the consequences of migration on both origin and
destination.

8.2  POPULATION TERMS
8.2.1 Birth Rate 
The Crude Birth Rate (CBR) is the normal number of live births per 1,000
populations regardless of sex and age composition. For example a population
of 35 million with 700,000 births a year will have a crude birth rate of 20 per
1000. The birth rate of a country is influenced by the age and sex structure of
its population and the family size preferred by the population.  Population
policies, of countries also influence the birth rate.  Where there are no
restrictions, a high population of young females in a population will yield a
high birth rate whereas a low population of females will result in low birth rate.
Birth rates of less than 20 per 1000 are regarded as low and are a characteristic
feature of industrialized, urbanised countries (Fellman, et al., 1999:100). 

8.2.2 Fertility Rate  
Fertility is the frequency of child bearing among the population. Fertility rate
refers to the relative frequency with which births actually occur within a
population. Crude birth rates are inaccurate in displaying regional variability
because the differences can be caused by age and sex composition or
shortcomings in births among the reproductive age rather than the total
population. Total Fertility Rate (TFR) is a more accurate measure since it tells
us the average number of children who would be born to each woman during
her reproductive cycle at the current years’ rate. For that reason, it is a more
reliable figure for regional comparative and predictive purposes than the crud 101
birth rate. A TFR of 2.1 is necessary just to replace present population (Ibid p.
101). The fertility rates of many less developed countries has been declining
because of the adoption of family planning methods and an increasing demand
over the costs of bringing up children today.

8.2.3   Death Rate    
The Crude Death Rate (CDR) also called the Mortality Rate (MR) is the
number of deaths per 1000 population. It is calculated in the same way as the
crude birth rate. The CDR is not an accurate figure for comparison across
nations unless the countries under consideration have the same age structure.
To overcome this lack of comparability, death rates can be calculated for
specific age groups.

The Infant Mortality Rate (IMR): Is the ratio of deaths of infants aged one year
or under per 1000 live births. i.e. deaths less than  1 year/1000 live births.
Mortality during the first year of life is usually greater than in any other year.
Therefore the drop in infant mortality accounts for a large part of the decline in
the general death rate. That is why Tanzania has given more weight to infant
immunisation. 

In many countries-Tanzania included, the various vaccinations given to infants
aim at reducing death rates in the above age category and that of the whole
population. Death rates are low in the rich countries, which is within the range
of 7 or less deaths per 1000 population and high in poor countries where 20 or
more deaths take place per 1000 population. In some parts of Sub-Saharan
Africa, the chief causes of death are infectious diseases such as malaria,
typhoid, cholera, diarrhoea and malnutrition. Sanitation plays a big role in the
reduction of mortality. Hence, there is a direct relationship between mortality
rate’s status of a country and its level of development.

 102
8.2.4 Natural Increase 
This is the increase of population caused by births. The rate of natural increase
of a population is obtained by subtracting the crude death rate from the crude
birth rate. By natural, we mean that increases or decreases caused by migration
are excluded. A country with a birth rate of 32 per 1000 and a death rate of
12/1000 will have a natural increase of 20 per 1000. Since the rate is expressed
as a percentage, in this example it would be 2%.

8.2.5 Population Doubling Time 
This is the time it takes for a population to double. The rate of increase can be
used to derive this. Population doubling time can be closely determined by
dividing the growth rate into the number 69. Thus a 2% rate of increase can be
expected to double in 35 years while that of 3% will double in 24 years!

?

How long will it take for a population with annual increase of
2.5% to double?

If the fertility is high accompanied with declining mortality, the doubling time
is shortened. This can compromise development efforts as the government
might not have enough time to tape resources and provide the basic services to
its population. Thus a slowly growing population is preferred. 

8.2.6 Population Pyramid 
A population pyramid is a graphic form of a pyramid drawn to express the age
and sex composition of a human population. The age groups are in the vertical
scale, starting with the youngest at the base and the number or percentage of
males and females within each of the age groups on the horizontal.

A pyramid with a wide base and narrowing upwards is termed expansive. It
indicates a young expanding population with many children and a declinin 103
death rate. If the shape resembles a tall dome, it is termed stationery, denoting a
stable, slowly growing population where there is decline in mortality and low
birth rate (refer to Figure 8.1). 

Figure 8.1: Population Pyramids of four Population Structure 
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Fellmann et al 1999:107 

The population pyramid is important in the analysis of population data as it
provides a quick visualised demographic picture of immediate practical and
predictive value. For instance, a country with a high proportion of young
population has a high demand for educational facilities and health delivery
services. It also means that a large proportion is too young to be employed.
Conversely, if a large proportion is of old people, it means that, many people
have to be supported, by a smaller proportion of the productive population. If
this population does not possess advanced technology, it may fail to support
dependants and fail to bring about development. Therefore, there is a need to
manage well fertility, in order to have a balanced population and hence avoid
negative effects arising from a young or aged population structure.

8.2.7 The Dependency Ratio 
Is a simple measure of the number of dependants; old and young that each 100
people in the productive years (15-64) must support. Population pyramid 104
provide a visual evidence of that ratio. They may also foretell future problems
resulting from present population policies and practices. It is predicted that by
year 2010 China will have about one million excess males a year entering the
marriage market because of earlier preference for sons in the implementation of
the one child policy.

?


Will such bachelors without families pose any social problems to
China?

Governments when planning for fertility control, should do so with long term
precautions to avoid sex and age imbalances in future.

8.3 POPULATION DISTRIBUTION
Human population is unevenly distributed over the earth. Some land areas are
densely populated, others sparsely settled while others are completely
uninhabited. More than half of the population live on about 5% of the land and
two thirds on 10%. Further analysis reveals that almost nine tenths of human
population inhabit less than 20% of land. In addition, 80% of the population is
found to live on land below 500 metres in elevation. More than half of the
world’s population is found in rural areas and more than 40% are largely
urbanites with a big proportion of this residing in very large cities. About 35-
40% of all the worlds land surface is inhospitable. (Fellman, 1990:122). A
number of factors are responsible for this situation.

Temperature, length of growing season, slope and erosion problems limit
habitation in high altitudes. However, not all lowlands are suitable for
settlement. Much of the population lives on alluvial lowlands and river valleys.
Generally, latitude, aridity and elevation limit the attractiveness of many areas. 
 105
Great clusters of population are East and South Asia, Europe, north-eastern
United States and South-eastern Canada. East Asia, including Japan, China,
Taiwan, and South Korea contains 25% of all people on earth. South Asia
comprising Bangladesh, India, Pakistan and Sri-Lanka account for another 21%
of the world’s inhabitants. This is close to half of the world’s population.
Europe accommodates another 13% of all inhabitants (Ibid). 

?

What are the factors that have influenced population
concentration in those areas?

The African population is concentrated mainly in areas with reliable rainfall
and natural fertility. Therefore, rainfall and soil fertility are determinants of
population distribution in Africa and Tanzania in particular. Areas like the
Southern highlands and the slopes of Mount Kilimanjaro which get sufficient
rainfall of over 800mm per annum, are more densely populated than the poorly
watered areas like Singida (Yanda and Shishira, 1999: 9): This is observable at
district level as well. For instance in Kibondo district in Western Tanzania,
60% of the people live in the western highlands which get more than 1000mm
of rainfall per annum (URT and Caritus, 1999:x). 

8.4 POPULATION DENSITY
The term density, expresses the relationship between the number of inhabitants
and the area they occupy. Although density figures are used widely, they are
misleading because not all land is habited. The calculation is an average and
thus does not reveal the quality of land, adequacy of food or levels of income.
Some of the inhabitants are made to this crude density by relating population to
that area that may be cultivated. When total population is divided by arable
land area alone, the resulting figure is the physiological density. This density is
able to reveal actual settlement pressures, which are not pointed up by the
crude density 106
The over all density of Africa is 16 people per square kilometre. This gives the
impression that there is no population pressure in Africa. However, the reality
is that the land suitable or open for human settlement is limited. For instance,
cropland accounts for 5-6% of total land area on the continent and in many
countries arable land available per capita is less than a half-hectare (White at
al., 2001:69; World Bank, 2001:288).

In Tanzania, only about 9% of the cultivatible land is of medium or high
fertility. The rest is of poor fertility and is either semiarid or infested by tsetse
fly. Since about 15% of cultivable land is already under cultivation, it means
that the best land is already cultivated (UN and UDSM; 1993). Subsequently a
growing population has to resort to areas with less suitable conditions for
agriculture. 

8.5 OVERPOPULATION
This applies to a situation whereby the population in an area cannot be
supported adequately by the available resources under the given technology.
When the number of people exceeds the optimum population, the standard of
living declines and both economic and social aspirations cannot be realised.

Overpopulation is not the necessary and inevitable consequence of high density
of population. This is because overcrowding is a reflection not of numbers per
unit area but rather of carrying capacity of land. The carrying capacity of an
area is the maximum human population that a particular area can carry or
support without suffering unacceptable deterioration given the prevailing
technology. When in an area, the population exactly equals the carrying
capacity, the area is said to have reached saturation level. The fact that carrying
capacity is related to the level of economic development, it follows that an area
that employs heavy use of irrigation, fertilisers and biocides can support more
people at a higher level of living than one engaged in shifting cultivation. 
 107
Based on the foregoing explanation overpopulation can be linked to levels of
living which reflect imbalance between numbers of people and the carrying
capacity of the land (Fellman et al., 1999:126). An indication of such
imbalance might be the inadequacy of food supplies to meet normal nutritional
needs. Bearing this in mind, many countries of Sub Saharan Africa can be said
to be over-populated since per capita food production has been decreasing for
more than two decades. 

From figure 8.2 below it is revealed that, Kenya, Uganda, Rwanda, Burundi
and Nigeria are overpopulated compared to Tanzania. 

Notwithstanding the above, in contemporary world, insufficiency of
domestically produced food cannot be considered as a sufficient measure of
overcrowding. Only few countries are agriculturally self-sufficient. Japan, one
of the developed countries with advanced technology imports about half of its
food requirements. The international trade helps to solve the problem of
overcrowding. Therefore, countries should strive to improve their economy.

8.6 POPULATION CONTROLS
Population pressure does not emanate from the amount of space humans
occupy. They stem from the food, energy and other resources necessary to
support the population. The declines in these factors that support population
impede the continuous increase of the human population. Famine and wars
have been recognised as the main checks on population in history. Thomas
Robert Multhus (1766-1834) in a treatise published in 1798 noted that
population is inevitably limited by the means of subsistence, celibacy and
chastity, war, poverty, pestilence and famine (Fellman, et al., p.130): Today
family planning through the use of modern contraception is the chief
mechanism that regulates population increase around the world.

 108
Figure 8.2: Carrying Capacity and Potentials in sub-Saharan Africa
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Fellmann et al 1999:126  

8.7 POPULATION MIGRATION
Migration refers to the act or process of moving from one place to another,
usually across a political boundary with the intent of staying at the destination
permanently or for a relatively long period of time. Humans move from home
areas to work or settle in another. Generally migration varies in volume,
distance and duration and it is divided into two main types, mainly internal and
external. Internal migration is when the movement is confined within the
country or particular region whereas international migration takes place when
the migrants cross international boundaries. In internal migration four major
types of migration can be discerned. These are rural-rural, rural-urban, urban-
urban and urban-rural. 
 109
8.7.1  Factors for Migration
Migration may be forced or voluntary or sometimes unwanted relocations
imposed on the migrants by circumstances.  Population growth, environmental
deterioration, increasing pressures on land, fuel and water, in the countryside,
international and civil conflict or war force people to migrate. 

In forced migrations the decision to move is made by other people other than
the migrants as was the case of millions of Africans who migrated to the
Americas and Caribbean Islands between the 16
th
 and 19
th
 century. Reluctant
relocation has been widespread in Sub Saharan Africa in the 1990s.
International refugees from political turmoil numbered over 28 million in this
period. Map 8:1 shows the main countries of origin and destination.

Figure 8.3:  Pattern of Migration in Africa in 1990s
QuickTime™ and a
 decompressor
are needed to see this picture.

Source:  Fellmann et al., 1999:84 110
Beside the above, the great majority of migrations are voluntary. Basically,
migrations take place because migrants believe that their opportunities and life
circumstances will be better at their destination than they are at the present
location.  Thus economic forces are primary in influencing people to migrate. It
has been observed that poor people may move from village to town and from
town to city being pushed by poverty and being attracted by opportunities.

Since poverty in developing countries is widespread in rural areas, rural urban
migration is overwhelming. Migrants are attracted to urban areas because there
are perceived opportunities in terms of income generation activities,
employment and social services. The expected positive attractions of migrants
at the area of destination are called pull factors while negative conditions at the
origin are called push factors. Thus migration is largely a product of both
perceived push and pull factors.

8.7.2 Consequences of Migration in Area of Origin and Area of
Destination
(a) Area of Origin
In the area of origin, where immigrants are unskilled, those who remain behind
are in high demand and wages rise. Emigrants usually send remittances,
thereby increasing the incomes of those who remain home. Remittances can
bring foreign currency when they act as an export commodity, as in the case of
Egypt, Turkey and Thailand. Migrant workers tend to make money servings to
buy cars, tractors and other consumables, which they take back to their
families. That way, they may raise the living standards of their families. If the
remittances are invested in production, the country can raise its Gross National
Product.

Nonetheless, there are negative consequences resulting from migration.
Foremost, there are social costs due to long periods of separation. Some
families break up permanently. Moreover when skilled professionals migrate 111
the country loses skilled people, a situation that leads to underdevelopment if it
is at a large scale. When most of the youth and especially males migrate and
stay for a long time, rural production declines as females fail to satisfy family
needs due to their dual role as producers and reproducers. 

(b) Area of Destination 
In the area of destination, supply of labour, increases and wages decline. The
host country can select migrants according to skills and education and employ
them thus gaining labour by giving low wages. On the other hand, this can lead
to high levels of unemployment if there are no vacancies. Additional
population also adds burden for provision of social services.

Socially, migrants may create tension in areas where they are concentrated. The
residents normally dislike migrants as the case in Western Tanzania where
refugees from Burundi and Rwanda have caused insecurity, destruction of the
natural environment and plundering of land resources. 

SUMMARY

Human population is the vital resource on earth. All other
resources are exploited depending on the skills acquired by a
population. Owing to this, it is very important to manage
population. Patterns and trends of human fertility affect and are
affected by the social, economic and political organisation of
society. High birth-rate for instance gives rise to a youthful
population structure with many dependants than producers. In
such a society, efficient methods of production are required in
order to support a growing population.

Total fertility rate is a useful measure of fertility than the crude
birth rate, as it allows comparison across nations. The difference
between births and deaths determines to a big extent growth rate
of population, which in turn determines the doubling time of 
 112



population. If the population doubling time is very short, problems
of maintaining the population arise. Thus population has to be
managed so as to control its rate of increase.

Human population is unevenly distributed over the earths’ surface
due to various factors such as temperature, degree of slope, soil
fertility, availability of water and mining activities. About 35%-
40% of the earth’s surface is inhospitable. Areas with great
concentrations of people experience population pressure on land
resources. Thus, the concept of carrying capacity is central to the
study of population and development.

Sometimes people fail to get their basic needs from an
environment and decide to migrate to another area. Migration has
both positive and negative effects to both area of origin and
destination. Hence, it is important to manage population in order
to avoid negative effects of migration.

EXERCISES


1.   Write short note son the following terms:
       Fertility rate, Birth rate, Death rate, Mortality rate, Population 
doubling time
2. Examine the factors which are responsible for population 
distribution pattern in your country.
3. “Overpopulation and under population are dynamic
conditions”. Elaborate this statement with focus to (a) the
concept of carrying capacity (b) technological advancement.
4. Why is a youthful population considered to be detrimental to 
development?
5. Discuss the pros and cones of population migration to both
the origin and area of destination 113

REFERENCES


Clark, Audrey, (1990); Dictionary of Geography. Geographical
Publications Ltd, London
Fellman J.D Arthur Getis and Judith Getis, (1998); Human
Geography: Landscapes of Human Activities, 6th edition.
The MacGrave Hill Companies, Inc.
United Nations and UDSM: Population, Environment and
Development in Tanzania, Dar es Salaam
White, H; T Kllick, S. Kayizzi-Mugerwa and M Savage (Eds).
(2001); African Poverty at the Millenium: Causes,
Complexities and Challenges. Washington D.C: The World
Bank.
Yanda, P.Z. and E.K. Shishira (1999); An Overview of
Agricultural Resources Base, Utilisation and Potential in
Tanzania Mainland. Report Submitted to the Ministry of
Agriculture and Co-operatives, United Republic of
Tanzania, Dar es Salaam
World Bank. (2001); World Development Report 2000/2001:
Attacking Poverty. www.worldbank.org/poverty/
URT, Ministry of Agriculture and Co-operatives: Lake Zone
Agricultural Institute, Maruku Agricultural Research
Institute and Caritas-Kigoma. (1999); Agriculture and
Food Security Survey in Kibondo District. Working Paper
No 28, 1999. Dar es Salaam, December.





 114
LECTURE NINE

AGRICULTURE


9.1 INTRODUCTION
Agriculture is a branch of science which deals with the cultivation of crops and
the keeping of domesticated animals for food, fibre or power. Economically, it
is the combined businesses of farmers, who produce commodities, input for
industries, which supply them with equipment, chemicals and finance, and
distributors of commodities to consumers.

Agriculture has replaced hunting and gathering as the main activity of
livelihood where environmental conditions permit. It is estimated that crop
farming covers some 15 million square kilometres worldwide, which is
equivalent to 10% of the earths total land area. In developing countries
agriculture is the leading economic activity employing about 75% of labour
force (Fellman, 1998:270). In highly developed economies only a small
proportion of the labour force is engaged in agriculture. For instance, in
Western Europe the labour force in agriculture is less than 10% and less than
3% in the United States of America.

Agriculture can be classified into subsistence, traditional (intermediate) and
advanced. In subsistence agriculture, production is solely for family
sustenance, using poor implements. Advanced agriculture is highly capitalised,
specialised, nearly industrialised, and meant for off farm delivery. In between
is traditional agriculture, where production is for home consumption, and partly
oriented toward marketing at local, national or international markets. This
lecture will concentrate on subsistence and commercial agriculture.

 115
OBJECTIVES


After reading this lecture you should be able to
(i) Differentiate subsistence from commercial farming;
(ii) Explain how agriculture is organised in China;
(iii) Discuss factors that contribute to success in agriculture in
North America;
(iv) Discuss the problems facing agriculture in Tanzania;
(v) Discuss the ways by which problems facing agriculture in
Tanzania are being solved.

9.2 SUBSISTENCE AGRICULTURE
This economic system involves production largely for self-sufficiency on part
of families. Production for exchange is minimal and each family relies on itself
for food and most essential needs. This system is predominant in most of
Africa, South and East Asia and Latin America where people are basically
concerned with feeding themselves from their own land and livestock.

Subsistence agriculture can be further divided into extensive and intensive
agriculture. The main difference among the two is their carrying capacity.
Extensive subsistence agriculture involves large areas of land and minimal
labour per hectare. Both population and yields are low. In contrast, intensive
subsistence agriculture involves cultivation with much labour per acre. Yields
per unit area and population densities are both high. 

9.2.1  Extensive Subsistence Farming
A form of extensive subsistence farming practiced in the warm, moist latitude
areas especially in Africa is shifting cultivation or slash and burn. It is one of
the oldest and most widely spread agricultural systems of the world. It is
practiced in parts of west central Africa, Northern part of Latin America and
East Indies. About 5% of people worldwide are practicing this agricultural
system whereas such type of agriculture covers 20% of the world’s are 116
(Fellmann, 1999:273). In Tanzania sparsely populated areas practice some
form of shifting cultivation. Outstanding examples are Dodoma, Singida,
Tabora, Kigoma, Rukwa and Mtwara.

Under shifting cultivation, farmers clear the natural vegetation, cut it into
pieces and then burn the cuttings. The cleared land is planted with crops such
as maize, millet, rice or cassava. The first and second harvests are usually good
but yields quickly decline with each successive planting on the same plot. This
is because soils lose most of their nutrients as they dissolve in surface and
underground water or by being used up by plants. 

When the soil becomes exhausted, the plot is abandoned for regeneration of
vegetation and a new plot is once again cleared and planted. Thus productivity
is maintained by rotating fields rather than crops. It can take 5-10 years before
the land left fallow can be re-cultivated. For this reason, each family requires
extensive land to support it. Hence, the system supports few people. Once
population increases, the fallow period has to be reduced and land is cultivated
before it can fully regain its fertility. At this stage it is necessary to employ
intensive methods of cultivation to maintain high yields. 

9.2.2 Intensive Subsistence Farming
Unlike the extensive subsistence farming which employ only 5 % of the
world’s population, more than 50% of the world’s people are engaged in
intensive subsistence farming mainly in India, China, Pakistan, Bangladesh,
Indonesia and some people of Africa and Latin America (Fellman et al, 1998).
Crops produced include rice, wheat, maize, millet and pulses. Intensive
subsistence farmers are concentrated in major river valley and deltas of the
Ganges and Yangtse and other lowlands with fertile alluvial soils. Here rice is
the chief crop grown and is used exclusively as human food. Let us turn our
attention to how the Chinese organize their agriculture.
 117
9.2.3    Agriculture Organisation in China
Planned agriculture in China was started after 1949 by the government. China
has managed to improve agricultural production by carrying out a
comprehensive national scheme for rice control of the great rivers such as the
Hwang Ho, Sikiang and the Yangtse. The river control project was
multipurpose and activities included control of floods, irrigation, and
generation of hydroelectric power. Also land reclamation, creation of navigable
waterways, research in agriculture and mobilisation of human resources for
development were other aspects addressed.

Under the river control scheme about five times the natural land was brought
under agriculture. Agriculture plans were set on duration of five years
beginning 1953. The aim was to formulate techniques and methods of
increasing agricultural output per hectare. Farmers were guided by eight
slogans:
1.  Fertilisation     2. Deep ploughing    3. Seed
improvement
4.   Close planting    5. Soil improvement    6.  Plant protection
7.   Tools improvement    8.  Irrigation

The government through rivers control project mainly undertook irrigation and
water conservation. Much of the work of expanding irrigation was done by
cooperatives and communes. With the formation of cooperatives and
production teams, much more labour could be mobilised to build large earth
dams and construct large network channels. This way, large areas could be
irrigated and more food produced.

• On soil improvement 
New and more efficient ways of mechanising soil were devised. Much
emphasis was put on composition and making use of seaweed and mud from
ponds to improve soil fertility. Agricultural colleges and research stations wer 118
responsible for developing quick maturing high yielding seeds. There was also
great emphasis on pests and diseases control. All major types of modern
pesticides and fungicides were introduced in large quantities. 

China demonstrates that in intensive agriculture, higher yields are a result of
high inputs. An increase in production of existing arable land rather than
expanding cultivated area has accounted for most of the growth of agricultural
production over the past recent decades leading to what is known as the Green
Revolution (Fellman et al., 1998:277).

• Green Revolution 
Refers to a complex of seed and management adapted to the needs of intensive
agriculture that have brought large harvests from a given area of farmland.
Between 1965-1995 world cereal production rose more than 90% and over
three quarters of that increase was due to increases in yields per unit rather than
expansions of cropland. This has been remarkable in Asia and Latin America
where between 1980 and 1992 yields increased by nearly 25% and 33%
respectively (Ibid).

Genetic improvements in rice and wheat have formed the basis of Green
revolution. Dwarf varieties have been developed that respond well to heavy
applications of fertiliser, resist plant diseases and can tolerate shorter growing
seasons. Adopting the new varieties and applying the irrigation, mechanisation,
fertilisation and the required pesticides have brought this success. However,
most of the poor farmers on marginal and rain fed lands have not benefited
from the new plant varieties that require irrigation and high chemical inputs.

Despite the high food production from the green revolution, there have been
negative effects too. Irrigation has destroyed large areas of cropland due to
excessive salinisation of soils resulting from poor irrigation practices.
Moreover, the huge amount of water required for Green revolution irrigatio 119
has led to serious groundwater depletion, constraining industrial water needs. It
is feared that most of the traditional varieties have been lost with the nutritional
diversity and balance that multiple crop intensive gardening assured. The poor
farmers who are unable to adopt it have been forced by circumstances to
migrate to urban areas. Thus the Green revolution has not benefited all people
engaged in agriculture. 

9.3 COMMERCIAL AGRICULTURE
Few people still practice subsistence agriculture per se as they have adjusted
their traditional economies in response to world trade. Nowadays, farmers
produce for their own subsistence and primarily for a market off the farm.
Farmers have become part of integrated exchange economies in which
agriculture is part of. Farming activities respond to market demand through
price. Thus production is related to the consumption requirements of the larger
society rather than the immediate needs of farmers themselves.

Agriculture in developed countries is characterised by specialisation by farm,
area and by country. Production is geared toward off-farm sale rather than
subsistence production. It is also characterised by interdependence of producers
and buyers through markets. Similar to subsistence agriculture, commercial
agriculture can be intensive or extensive.

• Intensive Commercial Agriculture 
Is characterised by application of large amounts of capital, high yields and high
market value per unit of land. Crops grown include horticultural crops such as
fruits and vegetables and farms are normally located close to markets. Included
in this type of farming is livestock –grain farming which involves the growing
of grain to be fed to livestock. In Western Europe for example, three quarters of
cropland is used for production of animal feed. In Denmark, 90% of all the
grains are fed to livestock and in turn farmers sell meat, butter, cheese and
milk. Unlike horticultural farms, these farms are located away from the mai 120
market centres because the value of the product per unit land is less than that of
dairy farms.

• Extensive Commercial Agriculture 
Mainly involves wheat farms and it is widely practiced in the North America.
The farms are very large. For example, nearly half the farms in Saskatchewan
are more than 400 hectares. Famous areas growing wheat include Kansas,
North Dakota, Eastern Montana and Southern parts of the Prairie Provinces of
Canada. Wheat farms require sizable capital inputs for planting and harvesting
machinery, abundant land facilitates, and large-scale farming which allow the
practice of leaving land under fallow. 

9.4    AGRICULTURE IN TANZANIA
Agriculture plays a central role in Tanzania’s economy. It accounts for 60% of
export earnings and 84% of employment. Outstanding components of the
agricultural sector are food crops, livestock and traditional exports whose
contribution stood respectively at 55%, 30% and 8% of the total agricultural
Gross product by late 1990s (URT, 1997:3).

An estimated 8% of land is under cultivation (UN  and UDSM, 1993: 13). Food
crops grown include maize, millet, sorghum, bananas, cassava, potatoes and a
variety of pulses. The principal export crops are coffee, cloves, cotton, tea,
cashew nuts, tobacco and sisal.

Arable land is undergoing accelerated rate of land degradation due to soil
exhaustion and erosion and desertification. This is particularly true in semiarid
ecosystems dominated by agro-pastoral communities. The problem of soil
erosion is prevalent, however in both areas of high agricultural potential as well
as in areas of low potential devoted to livestock keeping. The majority of the
smallholder subsistence farmers in Tanzania practice extensive subsistance
farming and small-scale livestock keeping. Subsistence farming is often linked
to environmental degradation because many farmers largely depend on th 121
local experiences rather than new improved methods of agriculture (Madulu,
2000:47).

The performance of the agricultural sector for the last two decades has been of
much concern particularly the period ending in the mid 1980s. Export
production declined between the 1970s and 1980s. This trend was accompanied
with the decline in the international prices of the traditional export crops. This
led to the drop in the real value of Tanzania exports. Consequently, the growth
rate of total exports declined at the average rate of 4.5% per annum while the
real value of imports grew at 0.7% annually over the period. A similar trend
applied to food crops and livestock where food crops declined by 0.2% per
annum between 1986 and 1991 while livestock registered negative growth
before the mid 1980s. There were no remarkable improvements made in the
1990s (Op.cit.). 

The withdrawal of government and its agencies from the provision of
agricultural services to farmers has not kept pace with the growth of the private
sector’s participation in terms of its ability to effectively take over these
services. Economic reforms have also affected cooperative unions. Debts and
bad financial conditions have constrained their ability to provide agricultural
services to farmers. Farmers cannot afford to buy fertilisers and other essential
agricultural inputs and tools. Lack of credit facilities to majority of farmers
prevents them from accessing inputs. The result has been unattractive farmer’s
incomes and accelerated poverty among them.

Poor agricultural performance in Tanzania is aggravated by the fact that some
suitable research findings often fail to reach the farmers. Lack of clear research
priorities and fragmented research activities adversely affect use of both
government and donor funds. Farming as an enterprise is currently dominated
by adult old farmers, a situation which threatens the maintenance of families.
So far the agriculture sector has failed to attract youths as a profitable venture
forcing them to migrate to towns and cities in search of other means o 122
sustaining livelihood. As a consequence of the above, there is food insecurity
and declining production of export crops.

Apart from the government allocating fewer funds than required, other setbacks
to agriculture include insufficient innovation and continued reliance on the
hand hoe, frequent droughts, land degradation, inadequate application of
fertiliser, and absence of linkages with industrial sector. Other problems are
over dependence on rain-fed agriculture, morbidity and poor nutrition. Lack of
reliable and profitable markets, pests and disease, and prevalence of Tsetse
flies also affect production. All this entails that poverty in its various
manifestations affects the performance of agriculture in Tanzania.
Improvement of agriculture has to do with strategies that are geared at reducing
poverty in rural areas.

9.4.1 Efforts towards Improvement of the Agricultural Sector in
Tanzania
To improve farmers’ knowledge in agriculture, several agricultural colleges
and Sokoine University have been established. Extension officers are trained
who in turn interact with farmers. Establishment of irrigation schemes and
construction of dams aim to solve the problem of unreliable rainfall and over
dependence on rain fed agriculture for example, Mbalali and Kapunga projects,
the Kagera and Rufiji Basin Development Authority. To overcome the market
problem, farmers are encouraged to form cooperative unions for organising
production and marketing of crops.

SUMMARY

Agriculture is an economic activity most extensively practised in
both subsistence and advanced societies. The form it takes first
responds to the immediate consumption needs of the producers
and then to needs of others. Whether it takes form of extensive or
intensive production, it reflects the environmental condition under
which it is practiced. 
 123




Extensive agriculture can be practised where farmland is
abundant. With land shortage and increasing population both
subsistence and commercial farming are bound to be intensive.
Farmers as part of integrated exchange economies respond to
market demands through price. There is interdependence between
producers and buyers.

Agriculture in Tanzania is partially subsistence and in part
commercial. The agriculture performance has been poor for three
consecutive decades beginning in 1970s. Lack of improving the
agriculture sector through government funding has left many
small farmers to continue with traditional systems of farming that
support low populations. With increasing population, poor
knowledge and lack of capital, farmers have failed to manage land
resources sustainably. Land has been degraded with an associated
result of declining yields. This has pushed most of the youth from
the agriculture sector such that, the sector is dominated by the
elderly.

EXERCISES


1. Compare and contrast subsistence and commercial systems of
farming.

2. How does extensive subsistence farming differ from intensive
subsistence farming.

3. What measures did China take to improve agricultural
production since 1949? What can your country learn from this
experience?

4. Examine the main features of commercial farming.
 124



5. Provide an analysis of manmade and environmental problems
facing agriculture in Tanzania. Suggest remedial measures.

6. What are the measures that have been taken by the government
of Tanzania to modernise its Agriculture?


REFERENCES

Fellman J.D Arthur Getis and Judith Getis, (1998); Human
Geography: Landscapes of Human Activities, 6th edition. The
MacGrave Hill Companies, Inc.
Kaduma, S (1994); Issues for Agriculture: “Challenges for the 21
st

Century”. In Msambichaka, L.A. H.P.B. Moshi and F.P.
Mtatifikoro (Eds): Development Challenges and strategies for
Tanzania: An agenda for the 21
st
 Century. DSM DUP 91-110
Madulu, N.F (2000); “Population dynamics and Natural Resource
Management in Tanzania”. In: Journal of the Geographical
Association of Tanzania NR 28 July 2000 p. 35-55
United Nations and UDSM: Population, Environment and
Development in Tanzania, Dar es Salaam
URT; (1997); Agriculture and Livestock Policy. Ministry of
Agriculture and Cooperatives, Dar es Salaam, January

URT (1998); The National Poverty Eradication Strategy, The Vice
Presidents Office, Dar, Govt Printer
White, H. T. Kllick, S. Kayizzi-Mugerwa and M. Savage (Eds)
(2001); African Poverty at the Millenium: Causes,
Complexities and Challenges. Washington D.C: The World
Bank.

 125
LECTURE TEN

EXPLOITATION OF NATURAL RESOURCES

10.1 INTRODUCTION 
Natural resources refer to natural wealth supplied by nature and available for
human use. They include mineral deposits, soil fertility, timber, energy,
waterpower, fish, wildlife and natural scenery. The list is not exhaustive
because what constitutes a resource depends on technological awareness, which
enables people to perceive it to be necessary and useful for their economic and
material well-being. The assessment of what constitutes a resource is
constantly changing with the development of technologies to exploit them. 

Natural resources result from physical processes over which human beings
have no direct control. If a substance is not known to be useful, then it is not a
resource. What makes people to perceive a substance as a resource is their
culture. Cultural awareness of its value and technology to exploit it are
therefore, fundamental in resource exploitation.

This lecture explores the exploitation of flow, stock and continuous resources
with particular focus on minning, forestry, fishery and tourism in Tanzania.
The lecture also puts emphasis on problems associated with the exploitation of
the three main categories of natural resources in Tanzania. 

OBJECTIVES
After going through this lecture, you should be able to:
(i)   Distinguish between renewable and non-renewable resources;
(ii) Assess the contribution of at least three natural resources to
the development of a selected country;
(iii) Evaluate the place of mining sector in industrial development
and economic transformation; 126


(iv) Evaluate the importance of tourism to national economies;
(v) Discuss the main problems encountered in the exploitation
of natural resources in your country;
(vi) Propose sustainable strategies for exploiting resources.

Natural resources are classified into three main categories as pointed out above.
Flow resources are those which are renewable, that means they are always
available and open to human modification. Humans or natural forces can
replenish them relatively quickly. Resources falling under this category
include, fish, soils, forests and water. Stock refers to non-renewable resources
such as minerals. Natural processes so far cannot replace minerals whereas
continuous resources are always available and independent of human action.
Examples include solar and wind energy. The first two categories can change
with time. For instance, renewable resources like forests and non-renewable
minerals such as gold can be exploited to extinction.

The maximum yield of a resource is the maximum volume or rate of use that
will not impair its ability to renew or to maintain the same future productivity.
In case of a forest, that level is marked by a harvest equal to the net growth of
the replacement stock (Fellman et al., 199:292). Overexploitation of a resource
causes this maximum volume to be exceeded, such that the renewable resource
turns out to be a non-renewable one. Therefore, the extent to which resources
can be exploited for sustainable development depends on the wise exploitation
of such resources. 

10.2 MINING
10.2.1  Coal 
This was the earliest mineral in importance in the world and is still the most
plentiful of the mineral fuels.  It was the first to be used as an industrial energy
source. Although coal is a renewable resource, world supplies are great; about
10,000 billion tons. Concentrations of coal deposits are found in the U.S.A an 127
China. Other major coal producers are Russia and Germany. Coal mining areas
attracted early industries such as iron and steel industries. These became
concentrated in coal rich regions like the Midlands of England, the Ruhr
district of Germany and the Donets Basin of Ukraine.

In Tanzania, coal occurs in the Ruhuhu and Songwe-Kiwira basins in the
Southwest   of Tanzania. A Total of about 1.5 billion tonnes in reserves have
been identified. The country’s only coal mine at Songwe Kiwira, has annual
output of 35,000 tonnes, all of which is consumed mostly locally for power
generation.

10.2.2  Petroleum 
Petroleum was first extracted commercially in the 1860s in U.S.A and became
a major power source. It is both a source of energy and a raw material in
fertiliser and plastic industries. Petroleum is unevenly distributed around the
world. About 80% of proved resources are concentrated in eight countries and
90% in 12 countries. Iran and the Arab states of the Middle East alone control
about two-thirds of the World total. 

The dependence of the United States and many other advanced industrial
countries on imported oil gave the oil-exporting states much power. For
instance, in 1973-74, and 1979-80 the selling price given by the Organisation
of Petroleum Exporting Countries (OPEC) was very high. The result was world
wide economic recessions for some importing countries and large net trade
deficits as more funds were used to import petroleum beyond the budget. Those
years are referred to as the “oil-shocks”. When the oil price declined in mid
1980s, economic activities were stimulated and hence increased use of oil.
OPEC countries include Saudi Arabia, Nigeria, Iraq, Iran and Kuwait.
 128
Although U.S.A does not have much deposits of petroleum, it is the second
producer in the world because it appropriates crude oil from the Middle East
and other African countries.

?

What mechanisms does the USA use in order to acquire crude oil
from the Middle East and other African oil producing countries?

10.3 MINING IN TANZANIA
Geological investigation carried out more than 60 years together with mineral
statistics show that Tanzania has a rich and diverse mineral resources base with
higher economic potential. These comprise gold, base metals and a wide
variety of gemstones such as Tanzanite, ruby, rhodolite and emerald. Other
minerals include coal, uranium, soda, kaolin, tin, gypsum and phosphate. Gold
and diamonds have always been the main stay of the country’s mineral
production. 

The mining sector contributes about 2.3% of the Gross Domestic Product
(GDP) which was projected to account for 10% of GDP in 2005 as stated in the
development vision 2025. It is one of the sources for generating foreign
exchange earnings within the non-traditional exports. In Tanzania the sub-
sector of mining industry is already a source of livelihood for over 0.5 million
people (Tanzania Government website, 2004). It has a potential of holding
back rural-urban migration, stimulating local processing and manufacturing
industry, thereby alleviating poverty.

10.3.1  Diamonds 
The bulk comes from the Williamson diamonds mine at Mwadui, Shinyanga
region where commercial production begun in 1925. Over 300 kimberlites are
known in Tanzania of which about 20% are diamondiferous.

 129
10.3.2   Gold 
Gold exploration has grown rapidly in the 1990s using modern technology and
refined models. Investigation has mainly focused on the greenstone belts
around L. Victoria.  Currently big gold mines are found in Kahama, Nzega and
Geita districts.

10.3.3   Tanzanite 
This is a gemstone unique to Tanzania. It is mined at Mererani in Arusha
region from weathered rock, sometimes in association with bands which are
also of commercial value. 

10.3.4   Natural Gas
Efforts made to explore petroleum along the coast are still underway.
Currently, natural gas is being mined in the south Eastern part at Songosongo
in Kilwa district. The gas is used to produce electricity and for domestic use. 

Over the decade, the global mining industry has undergone dramatic changes,
which may have far-reaching implications for Tanzania. The globalisation of
finance and investment and the deepening of financial mechanisms have
opened up new frontiers leading to the increase in the exploration and mining
development. New technology has allowed the discovery of deep-seated and
new deposits. 

The profound economic reforms and structuring undertaken by Tanzania
during the second half of 1980s and 1990s have marked a clear shift in favour
of private sector development and market-oriented economic management.
Consistent with the reforms, the role of the government has shifted from that of
owning and operating mines to that of providing clear guidelines, stimulating
private investment in mining and providing support for investors. Through
privatisation, foreign investors have dominated the mining sector.

 130
10.4 PROBLEMS ASSOCIATED WITH MINING IN TANZANIA
Despite the rich mineral endowment, Tanzania is among the four poorest
countries in the world. Efforts made by the government since independence to
develop the mining sector have not succeeded in mobilising the necessary
investable resources due to:
(a) Late recognition of the sector’s role in restoring the economy given the
changing economic environment.
(b) Lack of or absence of appropriate and consistent mineral sector policies to
provide an enabling environment for mineral development by the private
sector investment.
(c) Lack or absence of appropriate and consistent mineral sector policies
oriented towards private participation.
(d) Lack of adequate capital resources and their management
(e) Limited use of appropriate and advanced technologies
(f) Inadequacy of modern management and technical skills. The artisanal and
small-scale miners face technical, financial, marketing, social and
environmental problems.

In order to maximise its benefits to the country, there is need to improve the
management of resources to ensure that it contributes to poverty alleviation. 

10.5 FISHING
Fishing provide about 19% of animal protein intake of the developing world’s
population or 7% of protein supply worldwide.  People of Eastern and South
East Asia depend much on fish; which provide about 50% of animal protein. In
Africa and Latin America, fish provide between 15% and 20% of animal
protein. Moreover, about 70% of the world annual fish catch is consumed by
humans whereas only 30% is processed into fish meal to be fed to livestock or
used as fertiliser (Fellman, et al, 1998: 292). Reflecting from this, fish is very
important for a significant proportion of the world population.
 131
The same authors further point out that about 20% of the annual fish supply
currently comes from inland waters such as lakes, rivers and farm ponds. The
rest 80% comes from oceans mainly from coastal wetlands, estuaries and
shallow waters above the continental shelf. Waters in these areas supply
nutrients to plankton; an environment conducive for fish production

TAKE NOTE

Plankton is a minute plant and animal life that forms the base of the
marine food chain

Tropical fish species are less found in the commercial market due to their high
oil content. Nonetheless, they are of significant importance for local
consumption. Commercial fishing is predominant in the Northern waters where
warm water and cold water currents join and mix forming a congregation zone
for fish. Common species found include herring, cod, haddock and flounder.

10.5.1  Fishing in Tanzania
Tanzania is endowed with fishery resources. She has both marine and inland
fisheries potential. Tanzania has a coastline of about 800 km as its Exclusive
Economic Zone but due to poor fishing gear, it has not yet been fully exploited.
The marine water covers 64,000sq km, which includes the Indian Ocean, and
the Exclusive Economic Zone, which covers 223,000sq km. Fresh water
includes Lake Victoria, Tanganyika, Nyasa, and other minor ones. In totality
they cover 58,000sq km. 

The annual fish catch amount to 350,000 metric tons. There are about 80,000
fishermen who account for about 90% of the total fish catch in the country.
This means that only 10% is derived from Industrial fishing. Most of the fish
caught is consumed locally while the Nile Perch, sardines and prawns are
exported mainly to the European market.  Fish contributes about 30% of the
total animal protein intake of Tanzania’s population.
 132
Fishing is also a source of employment, livelihood to the people, recreation,
and tourism in order to create foreign income. The contribution of the sector to
Gross Domestic Product (GDP) since 2005 has been staggering between 1.6
and 3.1%. Even so, it contributes about 10% of total foreign exchange.

The industry remained uncoordinated until 1997, when a National Fisheries
Policy came into being. One of Tanzania’s Fisheries Policy is to increase
production and incomes of artisanal fisher folks by improving traditional
technology, modernization of infrastructure as well as by protecting the
country’s territorial waters. 

10.5.2  Problems of Fishing in Tanzania
Over fishing on the oceans is a leading problem affecting the fishing industry
because it is believed that oceans are common property and hence no one is
responsible for its maintenance or protection or even improvement. Since 1976,
coastal states have been claiming 370 km Exclusive Economic Zone (EEZ)
within which they are at liberty to regulate or prohibit foreign fishing fleets.
This is part of the United Nations Convention on Law of the Sea Treaty. Still
there is over fishing beyond the terrestrial waters – on the open seas. 

For example, on August 22, 2004 European trawlers were spotted illegally
fishing in Tanzanian waters. These are part of the 70 ships estimated to be
operating illegally, targeting tuna fish, kingfish, lobsters and prawns. It is
shocking to note that to-date, the sustainability of the industry is threatened by
over-fishing and use of destructive fishing methods such as, dynamite, and
poison whose ultimate impact is reduced catch per unit effort. The country is
losing a fortune to illegal fishing.

Improper handling technology, lack of storage facilities and poor transportation
facilities and infrastructure also constitute a big problem. About 20 percent of
Tanzania’s annual fish catch does not reach the consumer due to post harvest
losses caused by poor handling. To date Tanzania still faces a problem o 133
promoting sustainable exploitation, utilisation and marketing of fish resources.

10.6   FORESTRY
A forest is all land bearing a vegetative association dominated by trees of any
size, capable of producing wood or water regime or providing shelter to
livestock and wildlife. Forest resources include all wood and non-wood-based
resources in the forests.

According to Tanzania government website (2004), Tanzania has about 33.5
million hectares of forests and woodlands. Out of this total area, almost 2/3
consists of woodlands on public lands, which lack proper management. About
13 million ha of this total forest area have been gazetted as forest reserves and
over 80,000 ha of the gazetted area is under plantation forestry while about 1.6
million ha are under water catchments management. Public lands are under
great pressure from expansion of agricultural activities, livestock grazing, fires
and other human activities (URT, 1998:7).

The forests are of much benefit as they offer habitat for wild life, beekeeping,
unique ecosystems, and genetic resources.  Moreover, bio energy is the main
source of fuel for rural population accounting for about 92% of total energy
consumption in the country. Other services derived from the sector include
pasture for livestock, raw materials for industries, protection of watersheds,
source of water for irrigation, generation of electricity, environmental
protection, control of soil erosion and nutrients. Therefore, forests are an
important economic base for the country’s development.

The sector provides nearly 730,000 person years of employment that are
engaged in various forest activities. However, labour involved in the collection
of fuel wood and other products is not recorded. The sector’s contribution to
GDP is between 2.3 to 10% of the country’s registered exports. The wood
industry accounts for nearly 50% of the sector’s contribution to GDP. Non-
wood products and services contribute the other half. In 1999 only 26.269.7 134
cum were harvested from natural forests and 127,202.11 cum from plantations.
Export trade is mainly in fine hard wood timbers to earn foreign income (URT,
2004).

Since 1986 Tanzania embarked on policy and institutional reforms whose
overall objectives have been to restructure the national economy and facilitate
economic growth. Nonetheless, very little has been achieved.

10.6.1 Problems Associated with Forestry in Tanzania
(a) Tanzanian forests have great economic value if well cared. However, due
to inadequate management, the actual contribution of the forest sector to
the national economy is less significant. Wood fuels, gum Arabic, bee
products, game, catchments and environmental values have not yet been
adequately rewarded in Tanzania. 

(b) Deforestation is a big problem. There are no reliable data on
deforestation. However, estimates, range from 130, 000 to 5000,000 ha
per annum. The main reason for deforestation are clearing for cultivation,
overgrazing, wildfires, charcoal burning and overexploitation of wood
resources mainly in the unreserved areas. 

(c)  Inadequate forestry extension services and inefficient wood-based
industries.

(d)  Outdated machinery, poor transportation network, lack of working capital 
(< 1% of budget), non-reliable electricity and inadequate managerial
skills

(e)  There are varieties of ecosystems some of which have medicinal plants.
These ecosystems are threatened by human activities mentioned above.

(f)  Effective conservation of ecosystems has been impaired by lack of
sufficient coordination between the sectors (agriculture, wildlife, lan 135
development, water, energy and minerals) concerned and inadequate
knowledge among users.

(g)  Other problems include outdated legislation, fragmented administration at
all levels between the centre and the local levels, lack of participation of
various stakeholders in the management of the resources and poor data
bases, outdated and non existence of management plans for efficient
exploitation of resources.

As a result of the above problems, there has been deterioration of ecosystems
and soil fertility, reduced water flows and loss of biological biodiversity. The
demand for wood products is higher than supply for both domestic and export
markets. The utilisation of these resources could be developed through
multipurpose forest management, local processing and improved marketing
(URT, 1998:11).

TAKE NOTE

Ecology is the scientific study of the interrelationships between
living organisms and the environment in which they live.

Why do you think there is a need to coordinate activities of all
sectors related to ecosystems?

10.7 TOURISM
Tourism is the practice of making journeys for pleasure or for reasons of
business, inspection, education in several places or points of interest on the way
ending out the place of origin for more than a day. It is synonymous for tourist
industry that encompasses the whole business of providing hotel and other
facilities and amenities for those travelling or visiting (Clark, 1990:331).

Tourism is one of the world’s largest industries that are increasingly growing.
Being the largest business sector in the world economy, tourism employs abou 136
200 million people and generates about $ 3.6 trillion in economic activity. It is
an important industry in the economy of many countries in terms of job
creation and hence poverty alleviation (Pamba, 2004).

According to the World Tourism Organisation, Africa received 29.1 million
international tourists in 2002, which represented 4.1% of the world total.
Statistics also indicate that the Southern Africa region could have a growth of
over 300% in tourist arrivals by 2020. A similar impressive growth of 17% is
expected in East Africa. So with sound management Tanzania stands a better
chance of benefiting from tourism.

10.7.1 Tourism in Tanzania
Tanzania’s tourism sector is among the sectors, which contribute greatly to the
country’s economy. In 1997 tourism contributed 16% to the Gross Domestic
Product and 54% of export earnings employing about 157,200 people
countrywide (URT, 1999:3).

Tanzania is a beautiful country endowed with numerous tourist attractions. It
has 14 National Parks: These include the newly established park of Kitulo - in
Makete, 31 Game reserves and 38 Game controlled areas. Additional natural
attractions include the sand beaches in the north and south of Dar es Salaam
and superb deep-sea fishing at Mafia. Thus Tanzania’s competitive strengths in
tourism lie in abundant and diverse wildlife, varied landscapes and scenery.
Some of the outstanding attractions include: 

(a) Mount Kilimanjaro
With a snow caped tip is Africa’s highest mountain standing 5895m high close
to the equator (3°S). The mountain is an extinct volcano surrounded by dense
forests full of amazing variety of flora and fauna.

 137
(b) Serengeti National Park
covers an area of about 14763 sq kms and is the world’s wonder for its animal
variety and bird species.

(c) The Ngorongoro Crater
Once an active volcano, its cone collapsed about 8 million years ago. The
crater is 610 metres deep and 20 kms in diameter. It covers an area of 311 sq
km. The crater accommodates a crater lake and is the home of a variety of wild
game and birds.

(d) The Selous Game Reserve
The reserve extends for about 55000 sq km and is the largest wildlife reserve in
Africa. It provides sanctuary to the biggest elephant herds on the continent.

Tanzania is also well known for its rich heritage of archaeological, historical
and paintings sites. Among these is the famous Olduvai Gorge, situated in the
interior Rift valley. This is the cradle of mankind. 

The Tanzania National Parks (TANAPA)–established in 1959, manages the
parks, which occupy about 4.5% of the country’s total area. Despite the small
area they occupy, they play major role in biodiversity preservation and form
the backbone of nature-based tourism in Tanzania.

TANAPA manages national parks to ensure that there is a balance between
preservation and use. It is guided by a clear policy, which seeks to promote the
economy of the country and livelihood of the people, particularly poverty
alleviation. There is emphasis on the development of sustainable and quality
tourism that is culturally and socially acceptable, ecologically friendly and
environmentally sustainable (URT, 1999:5). These objectives are to be fulfilled
by the private sector, with the government providing conducive environment
for investment 138
TANAPA values and recognises the role of communities surrounding the parks
in achieving its conservation objectives. In this light it has an Outreach
programme for Community Conservation Services or Ujirani mwema with a
focus on local people and government at district level.

10.7.2   Community Participation in Tourism
Most tourist attractions lie within local communities or at least in their vicinity.
In some cases, tourist attractions co-exist with the communities and are sources
of livelihood (e.g. the lakes and the seas) while others have great significance
to the members within the communities. It is for these reasons that it is
important for communities living within or around these areas to fully get
involved in the development and management of these attractions within their
areas. Policy strategies for community participation include:

• Educating and sensitising community to appreciate and value tourist
attractions.

• Involving communities in the management of tourist attractions located
within their areas and the making of development related plans and
decisions with regard to tourist attractions especially where such plans are
likely to have a direct effect on the live hood and well being of these
communities.

• Involving local institutions such as the office of the District Executive
Director in the management of tourist areas, land and collection of revenue.

10.7.3   Tourism Limitations
The country has yet to exploit the full potential of the abundant natural
attractions and make Tanzania a favoured tourist destination. Areas that need
improvement include:
• Expansion of international air access. Though currently the Royal Deutch
Airline (KLM) flies daily in and out of Tanzania. The Tanzania Tourist
Board has to find means, which will enable the country to benefit fro 139
tourism by providing efficient transport to and within different tourist
destinations. Recently, introduced direct flight from Dar es Salaam to
Johannesburg by Precision air for example is one among such efforts.

• Provision of higher quality accommodation
• Most tourist attractions need to be better developed and utilized. The basic
infrastructure such as roads, water, power supplies, and communication need
to be improved or set in place. 

• Tourist products need to be better marketed and there is a need to advertise
tourist products so that they are well known worldwide.

•  Inadequate regional and international tourist linkages. The existing ones are
not fully capitalised for the development of the sector.

• There is poor coordination and inadequate land management for the
development of tourism.

• Shortage of appropriate and specialised core and skilled personnel in the
tourist industry accompanied by poor planning for human resource
development and investment.

• The inadequacy of awareness and appreciation especially on the part of local
communities, of tourism and the importance of setting aside and preserving
tourist attractions. 

• The deficiency in investment opportunities and limited indigenous and
community participation in investment activities within the tourist sector.

• The meagre resources of finance, as well as financial institutions to cater for
the development of the tourist sector (URT; 1999:3-4).

To conclude, tourism has a great wealth creation potential in Tanzania. Given a
conducive environment the wealth created through the proper management o 140
the industry could play a significant role in the alleviation of poverty
countrywide. The Ministry responsible for Tourism has the responsibility for
the development of Tanzania’s tourist industry and coordinate policies that
relate to tourism.

SUMMARY


Natural resources are supplied by nature. They include mineral
deposits, soils, vegetation, water and wildlife just to mention a few.
Resources become beneficial to human beings if the available
technology can exploit them. Culture enables people to perceive a
substance as a natural resource.

Resources are classified into three main categories, namely; flow,
stock and continuous resources. Bad management practices deplete
the flow resources while the stock resources become extinct.
Therefore, although natural resources are available for human use,
human beings have to ensure their sustenance. Advancement in
technology is fundamental in increasing the available volume of
resources for exploitation. That means resource consumption should
not exceed the maximum yield.

Tanzania though one of the poorest countries in the world, has great
development potential which lies in its abundant endowment in
natural resources, both renewable and non-renewable ones. The
country is blessed with diverse mineral resources of high value such
as gold, diamonds, coal, natural gas and Tanzanite. The country is
also rich in fishery, forestry and tourist attractions. All these if well
managed, can enhance development. The main constraints for
efficient exploitation of these resources are inadequate funds and
technology. 


 141
EXERCISES

1. Provide an analysis of the main determinants of resources
exploitation in a country or society.

2. Assess the role of the three categories of resources in the
development of your country.

3. To what extent is the mining sector important in industrial
development and the transformation of a county’s economy?

4. Examine the main problems facing the following sectors in
Tanzania:
(a)    Mining (b) Fishery    (c) Forestry     (d)   Tourism

5 Suggest workable strategies for your country for improving
the following:
(i)  The tourist industry
(i) The mining industry
(ii) The fishing industry
(iii) The forestry industry


REFERENCES


Clark, A.N (1990), The Penguin Dictionary of Geography.
Geographical Publications
Fellmann, J.D; Arthur Getis and Judith Getis (1999), Human
Geography: Landscapes of Human Activities, Sixth edition.
WCB/McGraw-Hill, Boston
United Republic of Tanzania (URT); Ministry of Natural Resources and
Tourism (1999), National Tourism Policy. Government Printer;
Dar es Salaa 142



United Republic of Tanzania (URT); Ministry of Natural Resources
and Tourism (1998), National Forest Policy. Government
Printer; Dar es Salaam
www.world -tourism.org
www.tanzania.go.tz/-24k 4/6/2004
www.ippmedia.com/ipp/financial/2005/11/09
















 143
LECTURE ELEVEN


APPLICATION OF STATISTICAL DATA IN
GEOGRAPHY

11.1 INTRODUCTION
Statistics is concerned with the scientific methods for collecting, organising,
summarising, presenting and analysing data. It also involves drawing of valid
conclusions and making reasonable decisions on the basis of such analysis
(Spiegel, 1981:1). Statistics can be located on the map to show the spatial
distribution or used to draw a graph to reveal differences. This gives a clear
visual impression, which is actually the main purpose of graphic data
representation. 

Data can be discrete or continuous. A variable, which can theoretically assume
any value between two values, is called a continuous variable whereas that
which assumes a fixed value is a discrete variable. For example, the number of
children in a family cannot be 3.12 and thus it is a discrete variable. On the
other hand, the age of a person can be 49.6 years; this is a continuous variable.
Data that can be described by a discrete or continuous variable are called
discrete and continuous data respectively. In this lecture you will be introduced
to various ways of summarising data statistically.

OBJECTIVES
After reading this lecture you should be able to:

(i) Describe the nature of geographical data;

(ii) List and discuss the common sources of data;

(iii) Discuss the common statistical measures used in presenting
and treatment of data;

(iv) Calculate the mean, the range and the standard deviation 144
11.2 SOURCES AND TYPES OF GEOGRAPHICAL DATA
There are many sources of geographical data. These can be population,
economic activities such as crop or industrial production, climate, and physical
data. Other sources of data are official sources such as government publication,
censuses and the international bureau of statistics. Data can also be obtained
from personal sources. These, include private collections and bibliography. 

TAKE NOTE

Datum is singular and data is plural.

There are four main types of data namely nominal, ordinal or ranked data, and
interval data.

11.2.1   Nominal Data 
Refers to objects, which have names such as land uses. Thus we can categorise
settlements as hamlets, villages and towns and later express them in percentage
of total land use.

11.2.2   Ordinal or Ranked Data 
Refer to objects, which have been placed in ascending or descending order. Dar
es Salaam, Mwanza and Tanga can be ranked 1, 2, and 3 in terms of their
population sizes without indicating their exact population figures.

11.2.3  Interval Data and Ratio Data 
Refer to real numbers. In interval data there is no true zero. This means that if
the temperature in Dar es Salaam is 34°C and that of Kibondo is 17°C, we
cannot state that Dar es Salaam is twice as warm as Kibondo. Ratio data on the
other hand possesses a true zero. It is possible to have 0 mm rainfall or 0 kgs
industrial production and so it is possible to say that Kibondo with 2000mm of
rainfall is about twice as wet as Dar es Salaam, which receives 1000mm per
annum 145
11.3 SUMMARISING DATA
In order to give meaning to collected data, it has to be summarised. Some
statistics are simple while others are very complex. However, the most basic
ones are simple descriptive statistics. These include measures of central
tendency such as the mean, the median and the mode.  

The mean is the average. It is a value, which lies centrally within a set of data
arranged according to magnitude. Several types of averages can be defined.
The most common is the arithmetic mean or simply the mean. This is found by,
totalling all values for all observations (∑n) and then dividing by the total
number of observations (n). For example the number of health centres in eight
districts is:

3,10,4,6,1,4,2,and 6. The average is 3+10+4+6+1+4++2+6= 36/8=4.5.
The mean is distorted if there is only one extreme value. Nonetheless it is the
most widely used summary because it can be used in further mathematical
processing.

Since there can be no half dispensary, we find that the mean is not always the
best statistic. Therefore, sometimes we use the mode. This is the most
frequently occurring number, group or class. In the example given above, 4 and
6 occur twice and these are modal groups. A pattern, which has two peaks, is
known as bimodal. The mode is very quick to calculate but it cannot be used
for further mathematical processing. Its other advantage is that it is not affected
by extreme values.

The average can also be found using the median. This is the middle value or
value above and below which there is an equal number of items when all
numbers are placed in ascending or descending order. The data given above
could be arranged as 10,6,6,4,4,3,2,1. When there are two middle values w 146
take the average of the two. In this case, 4+4/2 = 4. The median is not affected
by extreme values but it cannot be used for mathematical processing.

11.3.1  Summarising Groups of Data 
Sometimes the data we collect is best summarised in groups. This is very true
of population data. For example the population distribution of a hypothetical
place may be recorded as shown below and in order to find the mean age, one
has to multiply the midpoint or class mark of a class by the frequency. This is
called the long method. Adding the lowest value and the highest value and then
dividing by two gives the mid-point of a class. In the following table, the class
mark or mid-point of the first class is found by 4+0/2 = 2.

Table 11.1: Age Distribution of a Hypothetical Sample
Class Mid-point x Frequency (f) Mid-point *frequency
0-4 2 20 40
5-9 7 37 259
10-14 12 42 504
15-19 17 39 663
20-24 22 64 1408
25-29 27 58 1566
Total  N= 260 4440
  
The mean age  fx/N is 4440/260 =17.07 years 
The mean, median and mode provide a summary value for a set of data. On
their own however, we cannot get the idea regarding the spread of data around
the average value. The idea of how far data given differs from the average is
provided by measures of dispersion

11.3.2  Measures of Dispersion 
The range is the simplest way to show dispersion. It provides the difference
between the maximum and the minimum values. This is the difference betwee 147
the maximum (largest) and the minimum (smallest) values. It is limited on data
where there is significant variation between the records as in the case of rainfall
data. 

An alternative way is to find the deviation of the data from the median. This
gives the inter-quartile range. This is similar to the range only that it gives the
range of the middle half of the results. That means the extremes are omitted. It
measures the spread of values around the median. The greater the spread, the
greater the inter-quartile range.

• Method
1. Place the variables in rank order starting with the smallest and ending up
with the largest.
2. Find the upper quartile by taking the 25% highest values and finding the
mid-point between the lowest of these and the next number.
3. Find the lowest quartile by taking the 25% lowest values and finding the
mid-point between the highest of these and the next highest value.
4. Find the difference between the upper and lower quartile. This is the
inter-quartile range; a crude index of dispersion of values around the
median.

Example: 4, 5, 5, ↓ 7, 7, 9, ↓11, 12, 15, ↓15, 17, 17
      6              10                 15

The lower quartile is between 5 and 7. Their average is 6 (Q1). The median is
between 9 and 11 and the average is 10 (Q2). The upper quartile is between 15
and 15 and the average remains 15 (Q3). The interquartile range is found by
subtracting the lower quartile from the upper quartile (Q3-Q1). In this case, the
inter-quartile range is (15-6) = 9
 148
Sometimes the number of observations is not divisible by four. If for example
there are 21 observations, the quartiles are at 5 1/4 and 15 ¾.

In the following example: 75, 80, 84, 86, 125, 148, 184, 192, 195, 209, 210,
235, 274, 361, 390, 418,452, 460, 538, and 807, the 1
st
 Q 5 ¼ lies a quarter of
the way between 125 and 148. On the other hand, the 3
rd
Q 15 ¾ lies three
quarters between 361 and 390. 

The first quartile is found adding one quarter of the difference of 148 and 125
to 125 i.e. 125 +(148-125)/4 = 130.75

The third quartile is found by adding ¾ of the difference of 390 and 361 from
361 i.e. 361 + 3(390-361)/4 = 382.75. In this example, the interquartile range is
from 382.75 -130.75 = 252

The spread about the mean or standard deviation is another way of
expressing the spread of a data set. The greater the spread or range of data, the
less useful is the mean as a summary of data.

Method
1. Tabulate the values (x) and their squares (x²) Add the values of x and those
of x² (Σ x and Σ x²)
2. Find the mean of all the values of x⎯(x) and square it.
3. Calculate the formula
σ = √Σ x² -⎯x²/n  or √Σ (x-⎯x)²/n 


Where σ is the standard deviation, √ is the square root of, Σ  is the sum of, n is 
the number of occurrences in the set of data ,⎯x the mean of the values and (x-
x¯)² is the square of the difference between individual values. 
 149
Let us find the standard deviation for the following data set; 7,9,12,13,40,10
and 14. We first of all find the arithmetic mean as follows;
7+9+12+13+40+10+14 =105/7 which is 15. Subtract 15 from each value (x)
and find its square.

Table 11.2: Calculation of Standard Deviation for Ungrouped Data
x x-mean (x- x¯)  Σ(x- x¯)²
7 7-15= -8 64
9 9-15 = -6 36
12 12-15 = -3 9
13 13 –15 = -2 4
40 40-15 = 25 625
10 10- 15= -5 25
14 14- 15 = -1 1
  Total =784

The standard deviation S.D or σ pronounced as sigma is √784/7 = 2.64

For grouped data, we use the class marks (class mid-points) and frequencies to
calculate the standard deviation. The formula is: σ = √Σfx²/n –(Σfx/n)², where x
is the class mark and f the frequency. We not going into details about this
method. You will learn about it in higher levels.


The standard deviation is the best of the measures of dispersion because it takes
into account all the values under consideration. The smaller the number, the
smaller the deviation from the normal and vice versa.




 150

EXERCISES

1.  Describe the following terms: Discrete, continuous, individual
and grouped data.
2.   List and explain the common sources of geographical data.
3    Use the frequency distribution of masses of 6 students at the
Open University of Tanzania given in Table 11.2 to find the
mean, median mode and the mass standard deviation.
Comment on the spread of data around the mean.

Table 11.3: The Masses of Students at the Open University of Tanzania
Name Weight in kgs
Mary Katuku 61
George Damas 64
Ntila Wilfred 67
Naomi Rugano 70
Ruthbertha Abel 73
Anna Leba 67

4.  A student scored marks in seven subjects as follows: 74, 89,
64, 59, 85, 92 and 67. Determine the Arithmetic mean of the
marks.

5.  Find the range, the inter-quartile range and the standard
deviation  for the following set of data: 70, 94, 126, 98, 78,
102, 106, 82, 110, 122, 74, 86, 114, 90, 118.





 151
REFERENCES

Lines, Cliff, Laurie Bowlwell and Anne Fielding Smith (1996), A
Level Geography. Study Guide. Letts Educational, London.
Lenon, B.J and Paul .G Cleves (1983), Techniques and Field
Work in Geography. NNWIN HYMAN Limited London.
Nagle G and Kris Spencer (1997), Geographical Enquiries: Skills
and Techniques for Geography. Stanley Thornes
(Publishers) Limited. 

















 152
LECTURE TWELVE

GRAPHICAL REPRESENTATION OF GEOGRAPHICAL
DATA

12.1 INTRODUCTION
Geographic data can be represented quantitatively or qualitatively. When data
is represented qualitatively, it is merely described. For instance, in population
census we can shade a census map according to ethnic distribution, education
level or sex. When data is represented quantitatively, the actual numbers or
proportions are used. Statistical maps and charts are commonly used in data
presentation using cartographic methods. Three types of statistical maps used
include, choropleth, dot maps, and isopleth and flow maps. In this lecture,
focus is given to choropleth and isopleth maps.

12.2 GEOGRAPHIC METHODS
12.2.1  Choropleth Maps
These are maps in which areas are shaded according to a prearranged key, each
shading or colour type representing a range of values. You need a base map
and data for a given area. Find the area in your data and device a shading scale
accordingly (see Figure 12.1). You should have no fewer than four shading
types and no more than ten. Shading should be darker as the values increase.
Shade the aerial units and draw a scale on the map. The scale of choropleth
maps shows the number of items per unit area i.e. a relationship between
quantity and the area. It is commonly used to show variation in population
density.


 153
Figure 12.1:  Choropleth Map
Tanzania: Regional Variation in Levels of Poverty

• Work out the density per unit area (per square km)

• Choose a suitable scale to divide the values range into the number of classes
preferably with the same class interval for example, 10 units as in the case of
scalttergram classification. 

• Choose the shade or colour for high density and light colour for light density
or closeness of parallel increasing with the density. 

• Advantage 
Choropleth maps give an immediate impression of variations in values. They
can also be quantitatively interpreted in terms of the areas on which the data is
based.
 154

• Disadvantage of the Method 
The boundary line between each density zone gives an impression of an abrupt
change of density, which is a false impression. The shading relates to an
average figure for each area so variations within the area are not shown.

12.2.2    Isoline or Isopleth Maps
Iso means equal and pleth means value. Thus it is a line of equal value. Isolines
are lines drawn on a map, which join points of equal value in respect to a certain
phenomena such as contours on a relief map, isotherms of temperature and
isobars of pressure. They allow data to be plotted for a region without internal
boundaries interrupting the pattern. As such, they illustrate general trends with
changes in values shown smoothly.

Examples of isolines include; Isoneph which s a line joining all places having
the same amount of cloud cover per year
Isohel: A line that join places with the same amount of sunshine days or
sunshine hours per year.
Isohyt: A line joining all places with the same amount of rainfall
Isotherm: A line joining places with the same amount of temperature
Isobaths: A line that joins places of equal depth in the ocean
Isoseismals: Lines that join places with the same earthquake activity or intensity
Contour: A line that joins places with the same height above sea level
The result of these lines on a map is a pattern of lines showing distribution of
values or magnetic variation.





 155


Figure 12.2: A Contour Map of Rugunga Village in Western Tanzania





















LEGEND   Scale: 1:50,000





Source: URT; Ministry of Lands, Housing and Urban Development; Surveys and Mapping Division,
(1978).


 156

12.2.3 How to Construct an Isoline Map
Isolines can only be used when the variable to be plotted changes in a fairly
gradual way across space and where plenty of data is available. When drawing,
one must stick to the chosen interval. All isolines must have the same interval
between them.

(a) Firstly obtain an outline base map and then mark on it the points and their
values.

(b) Draw the isolines in pencil first.

(c) When you are satisfied that the lines accurately depict the distribution of
values, the lines can be linked and their respective values inserted.

(d) To enhance the visual impression, zones between successful isolines can
be cloured or shaded progressively heavier with increased values i.e the
higher the value of isolines, the darker the shading in atlases. Greens for
lowlands and white for very high mountains. You should establish a key.

(e) If you do not shade, then mark their numerical value

• Advantages of Isoline Maps
(i) Isoline maps are versatile, that means they are able to accommodate more
than one item of data such as crop data related to rainfall data.

(ii) Isolines are ideal for showing gradual changes over space and avoid
unreal effect which boundary linens produce on cholopleth maps (Lenan
et al, 1983:78).

• Disadvantages of Isoline maps
(i) Some data may be interpreted in different ways and this may produce
different isoline maps from the same data.
 157
(ii) A large number of data points increase the difficult of producing the map.

(iii) They are not suitable for partially distributions since a large amount of
data is needed for an accurate isoline map and a good deal of personal
judgement is always involved.

(iv) They disguise abrupt changes which may occur in features of human
geography from one locality to another.

(v) There is a high degree of subjectivity both in deciding where to locate the
values within areas and in the interpolation of the isolines.

• Flow Line Maps
Flow maps illustrate the movements or flows such as traffic flows along roads or
flows of migrants between countries. Observation of the movement is done at a
fixed checkpoint on the route or terminals, which may be a port, bus station or
an airport.

The volume of flow is shown by lines whose width varies proportional to the
volume of goods or numbers of people move to a certain route. A line is drawn
along a road or from the country of origin to that of destination, proportional in
width to the volume of the flow.
 
• Method
(i) Draw a base map of the route using a pencil.

(ii) Mark in all the fixed check points and the flow value in each point and
tabulate the data.

(iii) Choose the scale for the flow line width depending on: (a) the size of the
map (b) the data value range (c) the route net work density. Avoid to 158
large and too small scale. It is advisable to work out the width of the
highest value first. If the values are too high, use their square roots.

(iv) Convert all values to the scale and tabulate them.

(v) Draw the outline of the scale and tabulate them.

(vi) Draw the outline of the flow line in pencil and finally colour it. It should
be along roads or from the country of origin to that destination,
proportional in width to the volume. Note that a flow line map can show
a movement of goods in two directions, which means every side of the
route, will take full number of items (Ibid).

Figure 12.3: A Flow Line Map 
QuickTime™ and a
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• Advantages
(i) Flow data in statistical form is represented in much more easily interpreted
visual impression.

(ii) Problems of movement such as traffic congestion are shown clearly.

(iii) If a good scale is chosen, the map is easy to draw.

• Disadvantage 159
(i) A big range between data creates a problem for scale assessment i.e where
to start and where to end.

(ii) Lack of precise interpretation due to the lack of exact interpretation.

(iii) They create a problem in drawing a parallel double track.

12.3 STATISTICAL MAPS
These are sometimes called magnitude symbols. These include proportional
symbols, pie graphs, Bar graphs and population pyramids.

12.3.1    Proportional Symbols
These are symbols drawn on maps proportional in size to the size of a variable
being represented such as industrial out-put. More common of these symbols are
proportional spheres and cubes drawn three-dimensionally. However many
geographers use proportional bars and circles (Lanon et al., 1983:80). The
length of the bar or cube will be proportional to the volume it portrays. If they
are too short, the difference between them is hard to see. The bars are drawn on
the base map in the location where the phenomenon represented is found.

Since they are not commonly used, this lecture concentrates on graphs and
charts. You are therefore advised to find on your own how to draw them.

1.3.2 Pie Graph (Divided Proportional Circle)
It is a graph or circle representing the total values. It is divided into sectors each
sector being proportional to the value it represents. They involve some
mathematical calculations and are used to portray quantities such as population
which can be divided according to ethnic groups. The segments are proportional
to the components (Lenon et al 1983:73)

12.3.3    Method of Construction of Pie Charts
(a) Choose a convenient radius of the circle not too large or too small 160

(b) Divide the circle into segments proportions to values of individual
components. This is found as 
(i)    Percentage of total 
                   Component*100 
                     Total value
Where 100% = 360 degrees, then 1% = 3.6 degrees

(ii)   Component as the fraction of the total angle, calculated as a decimal
of the fraction of 360 degrees.

(c) The largest component should be placed to the right of the circle. The
small segments should be placed around 270 degrees to avoid error
accumulation due to pencil width.

(d) Printing on the chart should be printed in their segment.

(e) Small segments should be coloured to make them visible.

• Advantages of a Pie Chart
(i)   It has a striking and effective impression especially if coloured well.
(ii) It is easy to draw.
(iii) Two or divided circles can be used for comparison purpose provided they
are of the same size. The comparison should be on components not on
totals

• Disadvantages
(i) Pie charts lack exactness when compared to bar graphs because they have
no scale.

(ii) It is difficult to quantify any data on the pie chart without the angle
measurements.
 161
(iii) Accumulated pencil thickness may lead to the distortion of readings
particularly of small segments.

The following is the land use pattern in Kigoma region and how it can be
represented using a pie chart.

Figure 12.4: A Pie Chart
Landuse in Kigoma Region
14%
23%
9%
5%
49%
Agriculture
Forestry
Water
Others
Total

12.3.4    Simple Line Graphs
These are used for portraying the relationship between two variables, an
independent and a dependent variable. The independent variable is plotted on
the horizontal axis while a dependent variable goes to the y axis. The axes
should always start at zero.  Always mark on the axis what the variables are.
Care should be taken when choosing the scale in order to give a superb visual
impression.

A line graph is simple to construct, to interpret and to compare. Line used to
show variations or fluctuations of values over time. A line joins these different
data points. The line can be straight, with emphasis on size and fall. This is
prevalent in discrete data. The line can be carved to emphasise continuity of
data is in the case of temperature graphs. In both cases interpolation of values
is very difficult.
 162
• Method of Construction
(i) The horizontal line is used to show the independent variable such as
time, town or year.
(ii) The vertical axis represent the dependent variables which are values or
quantities in percentages or absolute numbers.

(iii) The base of y-axis must be above the last value. It is advisable to draw
two vertical lines on both sides of the horizontal line. Both lines should
bear the same scale and units.

(iv) Large numbers with many zeros should not be written on the scale.
Write tonnes in 00, 000 or kgm in 000 and then write number along the
scale.

(v) When plotting the graph do not use crosses but rather points.

TAKE NOTE

Be careful when choosing the vertical and the horizontal scale.
There should be no exaggeration. If two graphs are drawn for
comparison purposes, they should be of the same scale.


Figure 12.5:  Simple Line Graph
Year GDP % Growth  Year GDP % Growth
1990 6.2  1997 3.3
1991 2.8  1998 4
1992 1.8  1999 4.75
1993 0.4  2000 4.9
1994 1.4  2001 5.7
1995 3.6  2002 6. 163
1996 4.2   


QuickTime™ and a
 decompressor
are needed to see this picture.

Source: URT; Presidents’ Office- Planning and Privatisation (2003): The Economic Survey 2002,
Government Printer, Dar es Salaam, p.17

12.3.5    Comparative and Group Line Graphs
Method of construction
(i) Plot points for one item and join them and then distinguish the lines by
using different colours. If colours are not used then, join the points
differently.

(ii) Write the name of the items of represented on their respective lines on
the graph.

(iii) Avoid crossing of lines as much as possible to avoid confusion that can
impede interpretation. A key is essential.

(iv) The lines on one group should not be more than five 164




Figure 12.6: Comparative and Group Line Graph 

Trend of Coffee and Cotton Export Prices in Tanzania (US $/ton)
QuickTime™ and a
 decompressor
are needed to see this picture.


Source: URT; Presidents’ Office- Planning and Privatisation (2003): The Economic Survey 2002,
Government Printer, Dar es Salaam, p.62

12.3.6   Bar Graphs
Simple bar Graphs
These are used to portray information where one variable has a quantitative
value and the other does not. Bars are drawn  proportional in height to the value
they are representing. They can be drawn horizontally or vertically. Bars are
similar to line graphs in the method of construction. Bars are very impressive.
They give attention to individual amounts and their relative variations: They
represent a more concrete and definite quantity than a line graph. Thus, they
are more quantitative in aspect than line graphs.


 165




Method of Construction 
(i) The horizontal scale represents a dependent value. This can change when
you have horizontal bars. Bars can be drawn in groups or singly.
However, all bars must start at zero. If they are drawn for comparison
purposes, they should be drawn to the same scale.

(ii) Horizontal bars should be used when there is no element of time.

(iii) When vertical bars are drawn, the sequence of time is from left to right.

(iv) The scale of the graph should not be too small or too large. The width of
bars is not to scale.

(v) There must not be more than five bars together.


Figure 12.7: Simple bar Graphs
Population of Tanzani 166
QuickTime™ and a
 decompressor
are needed to see this picture.
Source:    Population Planning Unit and Bureau of Statistics (1995):  Population Development in
Tanzania, Dar es Salaam p. 5

Advantages
(i) Horizontal bar graphs allow the addition of more information 
(ii) Bar graphs can be drawn in conjunction with line graphs
(iii) A bar graph can acquire the idea of location when it is superimposed on
the map where the data was collected.

12.3.7    Comparative or Group Bar Graphs
In this type of a graph bars are used for comparison purposes. Each bar stands
for a particular item such as mineral or crop production. Whereas in line
graphs, the rise and fall of lines is used for comparison, in bar graphs it is the
length of bars that is used to compare items. The total length of individual bar
put together or indicates the total production of minerals or crop production in
that year.
 Figure 12.8: A Comparative Bar Grap 167
Population of Kigoma Region
Kigoma UrbanKigoma RuralKasuluKibondo
District
Population
1967
1978
1988

Source: Tume ya Mipango na Ofisi ya Mkuu wa Mkoa wa Kigoma (1999): Hali ya Uchumi na
Maendeleo ya Jamii Mkoa wa Kigoma  uk. 9

• Methods of Construction of Comparative Bar Graphs
(i) Choose a suitable scale and draw them as simple bar graphs.
(ii) To compare well, place the related bars close to each other. Usually the
longest bar is drawn to the extreme left and then progressing to the right.
 (iii) The bars for the values to be compared wit must be at the end of the
right.

(iv) Insert the key.

For convenience it is better to compare not more than four bars in one bar
graph. If bars represent two different phenomena, the scales must be two.
For example: one for crop production and the other for rainfall.

• Advantage of Comparative Bar Graphs
(i) They offer a good visual impression of the total values and that of
individual components 168

(ii) They are good in comparing individual items.

• Disadvantages of Comparative Bar Graphs
(i) Group bar graphs do not give precise accurate information of the totals.
This can be avoided by drawing the bars as percentage of the total.

(ii) The attention is put more on quantities rather than the fall and rise 

The graph depicts the deviation of quantities from a mean value or certain
chosen value. The divergence bar graph is used to show the production trend
with reference to an ideal quantity. The bars help to predict problems before
they occur in production or consumption.



Figure 12.9:  Divergent Bar Graph

Annual Growth in Maize Production, 1985-199 169
QuickTime™ and a
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Source: Population Planning Unit and Bureau of Statistics (1995): Population Development in
Tanzania, Dar es Salaam, p.53

Method of constructing Divergence Bar Graphs
(i) The average should be given a zero value and must be thickened on the x-
axis.

(ii) The vertical axis should be scaled with positives above the zero line and
negative below zero line.
(iii) Observe the highest and lowest values and then choose a scale.

(iv)  Plot the values from the zero line.

12.3.8   Population Pyramid
This is another form of bar graphs. The vertical axis shows age groups in five
year intervals. The horizontal axis represents the actual number of people in
each age group. The males are usually plotted on the left and females on the
right of the vertical axis (Lenon, et al., 1983:74)
1985/86 1986/87 1987/88 1988/89 1989/9 170

The youngest age group form the base of the graph. The length of the column
or bars varies with either absolute values or percentage of the total of that sex
in the group. If the values are to be given in percentage, they are calculated as
follows: 
(i) Divide the number of males in each age group by the total number of
males times 100.

(ii) Divide the number of females in each group by the total number of
females times 100.

Method of constructing an Age-Sex Graph
(i) Obtain statistics from regional or national census report taking the
number of males and females separately.
(ii) On a graph or normal paper draw two vertical axes one centimetre apart.
Indicate males on the left and females on the right to represent the age
groups.

(iii) Construct the bars 5mm in width starting with one side then another.
Care should be taken when choosing the scale to avoid too having too
long bars.







 Figure: 12.10: Population Pyramid Graph of Tanzania 199 171
QuickTime™ and a
 decompressor
are needed to see this picture.

Source: Population Planning Unit and Bureau of Statistics (1995): Population Development in
Tanzania, Dar es Salaam, p.8

Advantages 
(i) When used for comparison they reveal interesting sociological aspects as
age groups with many or few people, age distribution of a developing or
developed country.

(ii) Represents a clear picture of population summary. The total can be easily
found.

(iii) When used for comparison, they can be superimposed

SUMMARY


Geographical data is best summarised and represented statistically
by using statistical maps, and charts. Each type of representation is
suitable for specific kind of data. It also has advantages and 
 172


disadvantages. Continuous data is represented using line graphs
while discrete data is represented by charts. It is therefore important
to critically analyse the data before choosing a particular method of
representation to use.

EXERCISES

1.  Using the following climatic data of a hypothetical place, draw
a vertical bar graph and comment on it.

Month  J F M A M J J A S O N D
Rainfall
in mm
5.2 5.2 5.2 0 17.8 48.1 61.7 33.8 26.5 63.5 18.0 2.5

2.  Use the following data to draw a horizontal bar graph and give
your own comments.
Cropland 6%,
Pasture 40%
Forest 48%
Water and wasteland 6%

REFERENCES


Lines, Cliff, Laurie Bowlwell and Anne Fielding Smith (1996); A
Level Geography. Study Guide. Letts Educational, London
Lenon, B.J and Paul .G Cleves (1983); Techniques and Field Work
in Geography. NNWIN HYMAN Limited London
Nagle G and Kris Spencer (1997); Geographical Enquiries: Skills
and Techniques for Geography. Stanley Thornes (Publishers)
Limited 
Population Planning Unit, Presidents’ Office, Planning
Commission, Bureau of Statistics, National Family Planning
Programme, Ministry of Health (1995); Population and
Development in Tanzania, Dar es Salaam
 173

 Tume ya Mipango na Ofisi ya Mkuu wa Mkoa wa Kigoma (1999);
Hali ya Uchumi na Maendeleo ya Jamii, Mkoa wa Kigoma,
Dar es Salaam
URT, The Vice President’s Office. (1998); The National Poverty
Eradication Strategy. Dar es Salaam: Government Printer
URT, The Presidents’ Office-Planning and Privatisation (2003):
The Economic Survey 2002, Government Printer, Dar es
Salaam.















LECTURE THIRTEE 174

TOPOGRAPHICAL MAP INTERPRETATION

13.1 INTRODUCTION
In the preceding lectures you learnt about the extent to which your land can be
developed to raise the standard of living of your society. Furthermore, you have
been exposed to methods of measuring, recording and interpreting phenomena
as geographers. In this last lecture, you will be further enlightened about
topographical map interpretation. The word topography is derived from a
Greek word topes, which means place. It is a term used to describe all physical
features of a given area. Topographic maps are small-scale drawings of part of
the earth’s surface to show location, landscape and cultural features.

It is important to represent parts of the landscape in order to facilitate easy
representation and interpretation of features.

OBJECTIVES
 After reading this lecture you should be able to: 
(i) Explain the common types of maps in relation to their
characteristics;
(ii) Calculate areas from maps using a variety of methods;
(iii) Calculate the bearing of a place through use of magnetic
compass;
(iv) Relate features on the map to those found on actual piece of land
i.e. use of large-scale maps;
(v) Discuss the advantages and disadvantages of topographical maps
compared to photographs.
(vi) Draw a relief section and calculate gradient and vertical
exaggeration

13.2 MAP 175
A map is a portion or part of the features of the earths surface drawn to scale on
a plane surface such as paper, card, plastic, cloth or some other material (Dura,
1990:1). The information given on a map sheet includes: 

The title of the map, the scale of the map, the indication of the North direction,
The key, the boundary and, the latitudes and longitudes or grid lines.

There are a number of maps. However, most of the maps are grouped into two
main types:-Topographic maps and statistical or distribution maps. The later
were covered in lecture eleven. Here, our focus is on topographic maps.

13.2.1  Topographic Maps 
These are small-scale maps, which show both natural and man-made features.
To make these maps aeroplanes are used to take pictures for an area for the first
survey. Later, only certain points on land need to be measured and surveyed.
When all the necessary data has been compiled it is then used to print and
produce maps. 

The actual surface of the land is rarely smooth. Nevertheless, this is represented
on a flat surface. The map must represent all surface relief on flat paper and the
mapmaker cannot show all these details. More often a mapmaker summarises
information about the landscapes represented. Reflecting from this situation,
maps are not true, detailed copies of portions of the earths surface (McMaster,
1978:5). Any topographical map is much smaller in size than the actual tract of
country it represents. In order to be more realistic the mapmaker must reduce
all the distances and areas on the ground in the same proportions. This constant
relationship of lengths on the ground to the shorter areas on the map is the scale
of the map.


13.2.2    Map Scal 176
A scale is the relationship or ratio between the distance on the map and the true
distance on the earth’s surface.
Scale = Distance on map/distance on earths surface

We can identify three main types of scale: statement scale, representative
fraction scale and linear scale.

13.2.3   Statement Scale
This is the map scale stated in words. The scale may be stated verbally for
example ‘one centimetre to one kilometre’.

13.2.4    Representative Fraction (R.F)
This is a means of expressing the relative size of a map or drawing in terms of
a fraction. R.F scale is frequently expressed as a fraction with the numerator as
one. The ratio means that one unit on the map represents a given number of
units on the ground for instance, R.F 1/100,000 or as a ratio 1:100,000. This
means that one unit on the map represents 100,000 units on the ground. If the
unit used is centimetres, it means that one centimetre on the map represents
100,000 centimetres on the ground (1 km. =1000m*100 cm)
Conversion can be done as follows:
(i)      One centimetre to two kilometres
 1 cm: 2 km
 1 cm: 2*100,000 or 1/200,000
 R.F =1:200,000

13.2.5    Linear Scale or Line Scale
Is a line showing the distance on the map that represents a given distance on
the ground. In many cases a linear scale is placed at the bottom of the map. It is
divided into two sections 177
(i) The large section to the right is divided into equal units from 0 towards
the end of the scale to the right. e.g 0 1 2 3 4 km. This is also called the
primary section.

(ii) The small section or secondary section: This is a small section placed to
the left of 0. It is subdivided into fractions indicating smaller units of
measurements such as  0, 250, 500, 750 metres.

m-1000-----500-----0----------1----------2-----------4----------5-km
         Secondary section    Primary section
Conversion of one scale into another

According to McMaster (1978:6) a scale can be converted into another as
follows:
(i) Given the R.F or ratio 
To find the number of centimetres to the kilometre divide by 100,000
(the actual number of cm in a km) by the denominator of the fraction e.g
1/250.000 write 250,000/100,000 which gives 40 cm to a kilometre.

(ii) Given the number of kilometres to a centimetre, to find the R.F:
Multiply 100,000 by the number of kilometres to the centimetres and
you will have the denominator of R.F  e,g.  two kilometres to the
centimetre, write 2*100,000 which gives 1/200,000.

(iii) Given the number of centimetres to the kilometre, to find the R.F: divide
100,000 by the number of centimetres to the kilometre in the scale. What
you get is the denominator of the R.F. For instance five centimetres to
the kilometre: Write 5/100,000, which gives 1/20,000.

13.2.6    Types of Maps by Scale
There are three common types of map scales; small, medium and large scale
maps. On a small-scale map the degree of reduction is much less and the rati 178
will be a smaller number. In East Africa small scale maps are drawn to the
scale of 1:1,000,000, 1:500,000, 1:250,000, 1:50,000. Medium scale maps are
drawn at 1:25,000, 1:10,000 and 1:2500.

TAKE NOTE


If a linear scale is doubled, areas will be quadrupled. It follows that
a map on a scale of 1:100,000 can show four times as much country
as one on the same sheet of paper at 1:50,000. 



?


Why is the denominator of a small-scale map larger than that of a
large-scale map? 
 
The type of the scale therefore determines the size of the map or the distance
on the map and the true distance on the earth’s surface.

13.2.7 Measurement of Distance along a Road or River
You need to follow the following procedure: 
(i) Divide the required route by light pencil marks into portions that are
nearly straight.
(ii) The next thing you should do is to measure carefully each of these
sections with dividers or the edge of a piece of paper and note down the
measurements.

(iii) Add the lengths of various sections together and measure the total length
on the linear scale.

13.2.8 Measurement of Areas
Areas can be regular or irregular in shape. It is very simple to find their areas.

 179
(i) Regular shapes
These are in form of rectangles, squares or rectangles. For a four-sized figure,
the area is found by multiplying the width times length. This implies that you
first measure the lengths. The area of a triangular shape is found by first
measuring the length of the base of the triangle, then measure the length of the
perpendicular from the base to the apex. The area is half the first measurement
multiplied by the second.

13.2.9 Calculation of areas of Irregular Shapes
Unlike the regular shapes, irregular shapes cannot be accurately done using
simple direct methods. What you need to do is: 
(i) Divide the required shape approximately into rectangles and triangles or
even circles.
(ii) Calculate the area of these shapes and add up the result.
(iii)  Another method is to divide the area into equal squares of known area.
(iv) Then count the number of full squares of known area and each part of a
square as half square and then add them together to get the total area.
Instead of dividing the area into equal squares, you can also trace the area to be
measured.
(v) Trace off the outline of the area to be measured on square tracing paper
and transfer the outline on square paper. 
(vi) Tick off all completed squires in the outline and add up the total
(vii) Mark with dots all the half squares. Add up the total and divide by two.
(viii) To get the total area add up the number of complete squares and that of
the half squares
(ix) Using the map scale provided, find the area of one square in order to
calculate the approximate total area

13.2.10  Striping Method
(i) Trace the shape of the area on paper to be measured.
 180
(ii) Draw stripes of uniform width to cover the whole area.

(iii) Calculate the areas of each strip, which is a rectangle. The area obtained
is the sum of individual strips and should be given in the same units of
the scale of the map.

Find the area of the rectangle and the two triangles, and then add up their areas.

Figure 13.1: Measurement of Area
 

13.2.11 Measurement of Direction
Geography deals with places in relation to others. In order to determine the
direction of a place, we need to choose one direction from which we can
measure other directions. So, for this purpose we normally use the North and
the needle of the compass used to measure direction points approximately
towards the north. This direction is usually indicated at the top of a sheet of
map or in the border. Where more than one north is given, stick to the true
north or simply north. The geographic position of a place on a map may be
shown using the following:

(i)  Place names      (ii)   Compass bearing     (iii)  Latitude and longitude 
(iv) Grid reference
 181
Names of places on maps are commonly used to locate position of an area or
places. In Tanzania names of places such as Kigoma, Bukoba, Dar es Salaam
are clearly indicated. However these have their disadvantages in that one name
can appear in two places. Moreover the name occupies much space on the map
than the area actually represented and thus difficulty to locate a place precisely.

13.2.12  The North Direction and Position of Places
Direction is best given using a compass. A compass is an instrument used to
find direction. It consists of a free-swinging magnetised needle which points to
the North and South magnetic poles. Using a geographic or true north,
Magnetic North or a grid north may show the north direction on a map. The
Geographic or true north is the direction towards the 90° North latitude.

Magnetic North is the direction shown by magnetic compass, which always
points to the magnetic north pole. This is situated to the left of true north and
varies from year by year in relationship to the true north. The grid north is the
direction towards the north in maps drawn to grid system.

13.2.13 Compass Directions
The compass directions are measured from the North along a 360° circle. The
eight compass directions are: North, North East, East, South East, South, South
West, West and North West. Each of these is 45° degrees from the next.

Using the compass direction, the direction is given as an arc in 360° beginning
from north, swinging right in a clockwise direction until you reach the point the
point you want to measure. Therefore the direction of north is 0°, East is 90°,
South is 180° and West is 270°. By using this method you are able to give an
accurate measurement of direction to a degree or even a fraction of it. The
direction of a place can be given with respect to another. 

 182
Figure 13.2:  Compass Directions



• Bearing of a Compass (or Direction)
Compass bearing shows the direction of a place in relation to another point
measured clockwise from 0° to 360°. The position of a point is given in degrees
which can further be divided into minutes and seconds. To find the bearing of a
place from another place you need to follow the following procedure:

(i) Join the two points. In our example below, join x and y with a straight
line.

(ii) At point x draw a line parallel to the north-south line given on the map.

(iii) Using a protractor, measure the angle of y from north towards line AB.
The bearing of point y from x is 130° or y bears 130° from x or y is South
East of x.

Up to this point you are now aware that some of the problems encountered
when using place names to determine location of places can best be solved by
combining names with bearing and distance. For example Kibaha is twenty
kilometres West of Dar es Salaam City 183
13.2.14  Latitude and Longitude
The position of a place can also be given using latitudes and longitudes.
Indeed, latitudes and longitudes provide the international reference system that
locates any place on the earth’s surface. These are the most geographical way
of giving position. For that matter, these measurements are always needed in
making accurate maps. Longitudes and latitudes are indicated on map margins.

Latitudes and longitudes are angular measurements from the centre of the earth.
That is why they are given in degrees, minutes and seconds of arc. Latitude is
measured northwards and southwards from the centre of the earth. It describes
how far north or south of the equator a place is. A circle joining places of the
same latitude at the earth’s surface is called a parallel of latitude. A longitude
on the other hand is an angular measurement eastwards or westwards from the
centre of the earth. A meridian of longitude is the shortest line that can be
drawn on the surface of the earth. It joins the North Pole and the South Pole.
Many countries have accepted the meridian of the Greenwich as the Prime
meridian from where other meridians are measured. It is 0°.

TAKE NOTE


The Greenwich is just a convention.  A country is at liberty to
choose any other meridian as its prime meridian for its
measurements.

Any point on the earth’s surface can be accurately pinpointed using these lines
as there is only one point on earth that corresponds to any one set of figures. To
be more precise, the N, S must be added to latitudes and E, W to longitudes.
When stating the position you must first give the latitude and then the
longitude. It is common to write minutes (´) and seconds (´´). For example the
location of Dar es Salaam is 6°48´S 39°12´E.  Large areas on the Atlas map
can also be located by using lines of latitude and longitudes.
 184


?

Using latitudes and longitudes, what is the location of your home
district?


13.2.15  Grid Reference
 Unlike latitudes and longitudes, Grids belong to the map and have no
relationship to the ground. The network of gridlines forms perfect squares. In
East Africa usually these squares have sides of 100 km, 10km and 1km. The
grid lines are numbered from a particular point, usually the South-Western
corner of the whole country. This is named the grid origin. From the origin all
vertical lines (eastings) are numbered eastwards. In contrast, all horizontal lines
are numbered northwards and they are called northings. The numbers at the top
and bottom of a map refer to vertical lines i.e.  the eastings. The numbers along
the left and right hand borders refer to the edges of a grided square.

The reading in a Grid system is referred to as a grid reference and is given in a
six figure number. Always remember to give the eastward direction and then
the northward direction. 

Figure 13.3:  Grid Reference
           30         31         32         33                 43
   
01 A.  
02   
03   185

For example, in the figure given above, point A: easting = 312 and northings
=013. The grid reference of A is 312013. When the point lies between two
grids, subdivide the square into tenths to get the third figure. In the figure 13.3
given  below, 2 is the fraction of the easting.

13.2.16   Showing Features on a Map
Relief: The relief of an area is the surface form of the ground, which show size,
shape, slope, etc., of the highlands and lowlands. The relief of an area may be
represented in many ways on a map. These methods include indication of spot
height, trigonometric points, hill shading, layer colouring and contouring. Our
attention is drawn to contouring. Nonetheless you are free to look for details
about other methods. 

13.2.17   Use of Contours
A contour is a line on a map connecting all places of equal height above sea
level. When you interpret contour lines you are able to get the size and shape of
highlands and lowlands. Contour lines never cross each other because no one
point can be at two different heights above the Mean Seal Level (M.S.L). On
very steep slopes they are close to each other but they cannot cross each other.

Contours are drawn in regular steps measured vertically from M.S.L. These
steps are called Vertical Interval (V. I) such as 100, 150 or 200 metres.  The V.I
is normally kept constant on a map and it is indicated in the margin of the map.
It is common to thicken the contour lines at a given interval in order to make
them easily identifiable. In many cases they are coloured in brown, orange and
red.

Contour lines are numbered along them to indicate their height above M.S.L. 
in such a way that higher ground lies above the figures. From the numbering of
contours you can determine the direction of the slope and the height of the
numbered contour lines correctly 186
13.2.18   Some Facts about Contour Lines
(i) Contour lines close or join around hills, basins and depressions. In hills
the higher contours are in the middle.

(ii) Contour lines never cross each other.

(iii) Contour lines form a V-shape pointing upstream to denote a valley and a
V pointing down to denote a spur

(iv) In contour maps all contour lines close or extend to the map edge.

13.2.19    Land Forms on Contour Maps
(i) Highland landforms: These include, plateaus hills, ridges, spurs, slopes,
scarps, passes, saddles and watersheds.

(ii) Lowland landforms: These include gorges, levees, deltas, flood plains,
and V-shaped valleys.

(iii)  Coastline landforms: They include, estuaries, cliffs and corals, fringed
coastlines

Since you have already learnt how to represent these features using contour
lines in your O-level secondary education we will only remind ourselves how
to draw a cross section and calculate the vertical exaggeration and gradient.

13.2.20  Cross Section or Profile
Maps show relief in plan. It is important to visualise the appearance of the
features as they are seen from the ground. Constructing relief sections helps to
do this. The following are steps to be followed when constructing a relief
section (cross section).
 (i)   Identify the two end points of the required section on a map. Note their
positions and heights and the vertical Interval. Mark them as A and B
and join them with a pencil 187
 (ii)  Place the straight edge of a plain paper along the drawn line and mark
the end points A and B.

 (iii)  Mark along the edge of this paper the positions and heights of contours,
water features and important places that cut the line.

Figure 13.4: A Cross Section
QuickTime™ and a
 decompressor
are needed to see this picture.


(iv)  Remove the paper from the map and place it where you intend to draw
the cross section. The width of the cross section will be the distance
between A and B. Draw a line equal to the width.

(v)  Find the appropriate vertical scale to show the heights of contours such
as  1cm to 100m.
 188
(vi) Construct a frame for the relief-section by drawing perpendicular lines
from A to B and divide the heights into equal parts according to the
vertical scale you have chosen.

(vii) Place the marked paper along the base line so that AB on the paper lies
on AB on the framework.
 
(viii)  Mark each contour line along the horizontal line and proceed with others
according to their heights.

(ix)  Connect all the points with a pencil. You should smoothen hills and
valleys with a smooth curve.

(x)  Mark and label the required information. Indicate the North, add a title
to the cross section, as well as the vertical and horizontal scale.

TAKE NOTE


The horizontal scale is the map scale. The vertical scale is usually
exaggerated. 

13.2.21  The Vertical Exaggeration
This is the amount or number of times by which the vertical scale or height is
larger than the horizontal scale or distance. This relationship is important as it
determines the shape and size of features shown such that they are not too
small or too large.

V.E = Horizontal Scale
Vertical Scale
If the map scale is 1:50,000 and the vertical scale is 1 cm to 100m,
V.E = 50,000 = 5
10,000
 189
13.2.22   Horizontal Equivalent (H.E)
Horizontal Equivalent is the horizontal distance between two contour lines. H.E
is smaller when the slope is steep and larger when the slope is even or gentle.
Where there is a cliff there is no horizontal equivalent.

13.2.23  Gradient
Gradient is the slope of the land. It is expressed as a ratio between its Vertical
Interval and Horizontal Equivalent. Thus,
Gradient = Difference in height in metres 
   Distance in metres
For example, if the difference in height between two places is 100 metres and
the horizontal distance is 1,000 metres,
 G = 100  = 1/10 or simply 1 in 10
        1,000
This means that for every 10 metres of distance travelled the land rises by 1
metre. Gradient can also be expressed as an angle.

SUMMARY

The two main types of maps are topographic and statistical maps.
Topographical maps are small-scale maps and mainly show natural
and man-made features. These features are reduced in size on scale
to fit them on a map. Three common types of scale include:
statement scale, representative fraction, and linear scale. The three
scales are convertible from one to another.

On small scale maps actual distances are greatly reduced thus giving
a big ratio as opposed to a large-scale map. Distance on a map can
be measured using a pair of dividers, a piece of paper, or thread and
then placed along a linear scale to get the actual distance. 
Measurement of area of both regular and irregular shapes is also
possible using mathematical procedures 190

 Geography emphasises spatial location of phenomena. Thus
indication of location and direction of areas is very important.
Indication of the True North direction is important for measuring
direction of one place from another. The common ways of giving
the location of places or features is the use of place names, compass
direction, latitude and longitude and the use of grid reference.

Apart from measurement of direction, distance and area on maps,
we also show various features. Relief is well represented by contour
lines. In order to get their actual appearance on the ground, we draw
a relief section using two scales:- the horizontal scale and the
vertical scale. The horizontal scale is a map scale while the vertical
scale is chosen when drawing the cross section. Owing to this, the
actual size and shape of objects can be exaggerated. Therefore, after
drawing a cross section, you are advised to calculate the vertical
exaggeration in order to show the extent to which your features are
larger than if they were drawn to the scale of the map.

The land is not even. Sometimes we are interested in knowing the
slope or gradient of the ground. This is easily found by dividing the
difference in height by the difference in horizontal distance.


EXERCISES

1.    Using a given map of part of Rugunga village in Kibondo
district, Tanzania;
(a) Explain the kind of landscape represented on the map
(b) Calculate the approximate area of land shown on the
map.
(c) Find the bearing of Kavogoro hills from  Samvula hills.
(d) Give the grid reference for Samvula hills 191




Figure 13.5: Rugunga Map Extract 














Scale: 1:50,000
         LEGEND





Source: URT; Ministry of Lands, Housing and Urban Development; Surveys and Mapping
Division, (1978).

2.   If the scale of a map is 1:50,000 what length on the map will
represent a distance of 20 km on the ground.

3.    Look at the map of Africa and give its location using latitudes and
longitudes 192



4.   (a)   Draw a cross section from A to B on the following
hypothetical   contour map.

(b)  Calculate the vertical Exaggeration of the resulting cross-
section.



REFERENCES

Dura, S.E (1990), Map Reading and Photograph Interpretation for
Secondary Schools “O     ” Level. ILM Publishers Ltd, Dar es
Salaam.
McMaster, D.N. (1988), Map Reading for East Africa,  (4
th
 Ed),
Longman Tanzania Ltd, Dar es Salaam.