Geography Remedial Module 2014 PDF

PRE-UNIVERSITY REMEDIAL PROGRAM FOR THE 2014 E.C. ESSLCE EXAMINEES GEOGRAPHY MODULE WACHEMO UNIVERSITY Department of Geography & Environmental Studies Teaching material for: Pre-University Remedial Program for the 2014 E.C. ESSLCE Examinees Geography Credit Hours: 4 Hours Prepared by :Dr.Tesema Lendebo(PhD) : Melese Semebo : Alem Tesfaye (Assi.Pro.) Edited by: Tesfaye Letebo (Assist.Pro.) : Solomon Chufamo : Alemu Ersino Hosanna 2015 ii Table of Contents UNIT ONE...................................................................................................................................................................... 1 INTRODUCTION.......................................................................................................................................................... 1 1.1. THE SCIENCE OF GEOGRAPHY........................................................................................................................ 1 1.1.1. DEFINITIONS AND CONCEPTS...................................................................................................................... 1 1.1.2 BRANCHES OF GEOGRAPHY................................................................................................................................. 2 1.1.3 Scope/Coverage of Geography........................................................................................................................ 4 1.1.4 APPROACHES IN GEOGRAPHY............................................................................................................... 6 1.1.5 Major School of Thoughts in Geography........................................................................................................ 7 1.1.6. Relationship between Geography and other disciplines................................................................................ 10 UNIT SUMMARY........................................................................................................................................................ 11 UNIT TWO................................................................................................................................................................... 14 MAP READING AND INTERPRETATIONS............................................................................................................ 14 2.1 DEFINITION AND CONCEPTS................................................................................................................................. 14 2.2 USES OF MAPS...................................................................................................................................................... 14 2.3 CLASSIFICATION OF MAPS.................................................................................................................................... 15 2.4 MARGINAL AND BOARDER INFORMATION............................................................................................................. 16 2.5 CONVENTIONAL SIGNS AND SYMBOLS.................................................................................................................. 17 2.6. RELIEF REPRESENTATION ON MAPS..................................................................................................................... 20 UNIT THREE............................................................................................................................................................... 30 THE PHYSICAL ENVIRONMENT OF THE EARTH (30 HOURS)......................................................................... 30 3.1 PHYSICAL ENVIRONMENT OF THE WORLD........................................................................................................... 30 3.1.1 The Earth in the Universe............................................................................................................................. 30 3.1.2 Forces That Change the Surface of the Earth............................................................................................... 30 3.1.3. Weather and Climate.................................................................................................................................... 36 3.1.4 Natural Regions of the Earth........................................................................................................................ 57 3.1.5 Ecosystem..................................................................................................................................................... 65 3.2 PHYSICAL ENVIRONMENT OF AFRICA.................................................................................................................. 66 3.2.1 Position, Size, and Shape of Africa............................................................................................................... 66 3.2.2 Geological and Relief Structure of Africa..................................................................................................... 71 3.2.3. CLIMATE OF AFRICA.............................................................................................................................. 76 3.2.4 Drainage in Africa........................................................................................................................................ 83 3.2.5 Natural Vegetation and Wild Animals of Africa............................................................................................ 92 3.2.6. SOILS OF AFRICA..................................................................................................................................... 99 3.6.7. Problems and Conservation Measures of Soils in Africa............................................................................ 101 3.3. PHYSICAL ENVIRONMENT OF ETHIOPIA............................................................................................... 102 3.3.1. Geological Structure and Relief of the Horn of Africa............................................................................... 106 3.3.2. CLIMATE OF ETHIOPIA........................................................................................................................ 118 3.3.3. NATURAL VEGETATION AND WILD ANIMALS OF ETHIOPIA......................................................... 127 3.3.4. SOILS OF ETHIOPIA............................................................................................................................... 135 UNIT FOUR............................................................................................................................................................... 142 i HUMAN POPULATION (27 HOURS)...................................................................................................................... 142 4.1 CONCEPT AND FACTS ABOUT HUMAN POPULATION........................................................................................... 142 4.1.2. Components of Population Change............................................................................................................ 143 4.1.3. Spatial Distribution of Human Population................................................................................................. 144 4.1.4 Population characteristics........................................................................................................................... 145 4.1.5. Sources of Population Data........................................................................................................................ 145 4.1.6. Population theories.................................................................................................................................... 149 4.2 HUMAN POPULATION OF THE WORLD................................................................................................................ 153 4.2.1 Size and Trend of World Population Growth............................................................................................... 153 4.2.2 Spatial Distribution of World Population.................................................................................................... 156 4.3 POPULATION OF AFRICA.................................................................................................................................... 160 4.3.1 Aspects of Population, Economy and Natural Resources of Africa............................................................. 160 4.4 POPULATION OF ETHIOPIA................................................................................................................................. 176 4.4.1 Population Size and Growth Rate................................................................................................................ 176 4.4.2. Components of Population Change in Ethiopia......................................................................................... 181 4.4.3. Population Structure of Ethiopia............................................................................................................... 185 4.4.4 Impacts of Rapid Population Growth.......................................................................................................... 190 4.4.5. Population Policy of Ethiopia.................................................................................................................... 191 4.4.6. Urbanization.............................................................................................................................................. 194 UNIT FIVE................................................................................................................................................................. 200 ECONOMIC GROWTH AND SUSTAINABLE DEVELOPMENT (21 HOURS)................................................... 200 5.1. ECONOMIC ACTIVITIES..................................................................................................................................... 200 5.1.1 Classification of Economic Activities.......................................................................................................... 200 5.2 NATURAL RESOURCES........................................................................................................................................ 206 5.2.1 Classification of Natural Resources............................................................................................................ 206 5.2.2. NATURAL RESOURCES OF AFRICA AND ITS POLITICS................................................................... 207 5.3 ECONOMIC SYSTEMS.......................................................................................................................................... 213 5.4 CONCEPT AND INDICATORS OF ECONOMIC DEVELOPMENT............................................................................... 215 5.5 SUSTAINABLE ECONOMIC DEVELOPMENT.......................................................................................................... 220 5.6. GLOBALIZATION............................................................................................................................................... 220 5.7 ECONOMIC GROWTH AND DEVELOPMENT IN ETHIOPIA..................................................................................... 222 5.7.1 An Overview of Economic Growth and Development Trend in Ethiopia..................................................... 222 5.7.2 Major Features of Ethiopian Economy....................................................................................................... 223 5.7.3. Challenges and Prospects of Socio-Economic Development for Ethiopia................................................... 225 ii 1 UNIT ONE INTRODUCTION 1.1. The Science of Geography 1.1.1. Definitions and Concepts  Ancient Greeks defined geography for the first time. They combined two words: -Geo – which means earth -Graphic – which means writing From the ancient Greeks to modern-day geographers, geography has been defined differently. However, the various definitions share some common ideas. Here are some of the most important definitions that geographers have proposed:  Eratosthenes (276-196 BC) – Geography is the description of the earth.  Concise Oxford Dictionary (1964) – Geography is the science of the earth’s surfaces.  Hartshorne, R. (1899-1992) – Geography is a branch of knowledge that is concerned with the provision of an accurate, orderly and rational description of distributions on the surface of the earth.  Yeates, M. (1968) – Geography is a science that is concerned with the rational development and testing of theories that explain and predict the spatial distribution and locations of (things and) phenomena on the surface of the earth.  As you can see, each of these definitions includes the idea that geography studies the earth. Most of them specify the surface of the earth; emphasized the fact that geography is a spatial science.  In the mid-20th century, it became a spatial science dealing with the arrangement and distribution of things and phenomena over the surface of the earth.  Geography has now become a science that examines “place and space” on the Earth’s surface in relation to location, distribution, arrangement, interaction, causes and effects of (things and) phenomena.  Modern geography is a spatial temporal-areal science. Accordingly, geography can be defined as “the study of the spatial distribution of both physical and human-made things and phenomena on the earth’s surface and the two-way interactions and interdependences between natural and human environments.” While making spatial investigations, geographers ask at least the following five pertinent questions about the phenomena they study. These are: 1 “WHERE are things located?” “WHY are they located where they are?” “WHEN did the things form?” “WHAT things are found where?” and “HOW are they arranged?” What makes geography a science? Science is a system of acquiring knowledge through scientific methods. These methods involve: observation, identification, description, experimental investigation, and theoretical explanation of phenomena. Geography investigates facts and relationship related to physical and social phenomena, and examines their distribution across the world and changes over time. The main tools geography uses to gather and analyze information are observation, systematic description, systematic recording and mapping. These facts make geography a spatial science 1.1.2 Branches of Geography Geography has two main branches of study - - A. Physical geography and B. Human geography A. Physical Geography This branch of geography studies the distribution of the natural features of the world, such as climate, landforms, soil, vegetation, and drainage systems. Physical geography also considers causes, effects and interactions of these features. Physical geography includes:  Climatology: studies factors that create climate and examines the variation and distribution of climate and related causes and effects.  Geomorphology: studies the distribution of landforms (such as mountains and plains) and the forces that change them.  Soil geography: studies the distribution of soils and their characteristics. 2  Biogeography: studies the distribution of plants and animals in relation to the environments that they inhabit.  Oceanography: studies the location, causes and effects of ocean currents, waves and tides.  Hydro Geography: deals with the water resources, the distribution and use of water across the planet  Cryosphere Geography: Cryosphere geography explores the ice of the earth, especially glaciers and ice sheets. B. Human Geography This branch of geography studies the distribution and influence of human aspects of our world, including cultures, population settlement, economic activities and political systems. Human geography includes: Cultural geography: studies the distribution and interactions of cultures, including peoples’ beliefs and customs. It also examines the movement, expansion and interaction of cultures on the surface of the earth. Population geography: studies the distribution, growth and structure of population. Economic geography: studies production, consumption and exchange and the spatial distribution of goods and services and factors affecting them. Political geography: studies the distribution of political systems and the ways people use them to exercise power and make decisions. Urban geography: studies the development and characteristics of towns, cities and other urban centers. Historical geography: is the study of the geography of the past and how places or regions change over time. Transportation Geography: deals with the History of transport, modes and needs of transport systems, networks and models of transportation, cost of transport and accessibility and connectivity. Medical Geography: Medical geographers study the geographic distribution of disease (including epidemics and pandemics), illness, death and health care. Recreation, Tourism, and Sport Geography: The study of leisure-time activities and their impact on local environments, among others. 3 1.1.3 Scope/Coverage of Geography The scope of Geography is the surface of the Earth. The geo-sphere is considered as geography’s scope. The geo-sphere itself is made up of the following sub spheres:  Atmosphere(air),  Lithosphere(land),  Hydrosphere(water) and  Biosphere(living things),  Anthroposphere (earth’s cultural landscape) which provides the habitable zone in which humans are able to live. The geospheres of the earth 1.1.4. Themes and approaches of Geography  Basic themes in Geography  Geography has five basic themes namely:  Location,  Place,  Human-environment interaction,  Movement, and  Region 4 1. Location:- is defined as a particular place or position. Location can be of two types:-  Absolute location and Relative location Absolute location (also known as astronomical location or mathematical location).Is defined by its exact address or it can be defined by:- Latitude (is the distance north or south of the Equator and is expressed as a number between 0 and 90 degrees north or south, and Longitude (is the distance east or west of the Prime Meridian and is expressed as a number between 0 and 180 degrees east or west. 2. Place Place refers to the physical and human aspects of a location. Place is associated with:- Toponym (the name of a place), Site (the description of the features of the place), and Situation (the environmental conditions of the place). Each place in the world has its unique characteristics expressed in terms of physical aspects like landforms, hydrology, biogeography, pedology; human aspects like characteristics and size of its human population, and the distinct human cultures. The concept of “place” aids geographers to compare and contrast two places on Earth. 3. Human-Environment Interaction Humans have always been on ceaseless interaction with their natural environment. No other species that has lived on our planet has a profound effect on the environment as humans. Human-environment interaction involves three distinct aspects: dependency, adaptation, and modification.  Dependency refers to the ways in which humans are dependent on nature for a living.  Adaptation relates to how humans modify themselves, their lifestyles and their behavior to live in a new environment with new challenges.  Modification allowed humans to “conquer” the world for their comfortable living. 4. Movement Movement entails to the translocation of human beings, their goods, and their ideas from one end of the planet to another. So, the three dimensions of movement include: physical movement of people; the transport of goods and the flow of ideas 5 5. Region A region is a geographic area having distinctive characteristics that distinguishes itself from adjacent unit(s) of space. Region could be:-  A formal region (natural regions) that is characterized by homogeneity in terms of a certain phenomenon like soil, temperature, rainfall, physical conditions, etc.  A functional region or nodal region characterized by functional interrelationships in a spatial system. Ex: Town-region which is interdependent with surrounding rural areas 1.1.4 APPROACHES IN GEOGRAPHY The most frequently adopted approaches are: A. Topical or Systematic Approach B. Regional approach A. Topical or Systematic Approach: The topical or systematic approach applies a specific geographical element or phenomenon over a defined geographical unit. For example, it takes a phenomenon such as climate, land forms or culture, and treats the distribution of the selected element over a country, continent or the world at large. Examples of topical approaches to study geography:  The geography of hunger  The geography of climate  The geography of agriculture  The geography of population B.Regional Approach A geographic study that uses the regional approach focuses on a region – a defined geographic unit or locality. Within the region, the study examines a variety of geographic features. The region studied could be a subcontinent, continent or a number of countries that share a common geographic factor. Examples of regional studies:  The geography of Africa, Asia, or Oceania, etc  The geography of sub-Sahara.  The geography of the Middle East.  The geography of the Balkans. 6 1.1.5 Major School of Thoughts in Geography Various schools of thought have emerged with different views regarding the relationship between humans and their environment as well as the interpretation of social problems by human. A.School of Environmental Determinism  The idea of environmental determinism was laid down by Greek and Roman scholars.  Is a philosophy that bases its view on the idea that the natural environment is an influencing factor on humans’ mode of living.  It believes that human activities are controlled by the environment.  It was the dominant idea up to World War I.  It advocated that the physical environment directs the day-to-day activity of people.  It advocated that the physical environment is the master in determining the day-to-day activity of people.  The physical qualities of geographical conditions are the causes:- -for people’s physical differences; -for differences from place to place in people’s economic activities, cultural practices and social structure.  It tends to focus on the impact of the physical environment on people, rather than the reverse the influence of people on the environment. Determinists consider human beings as passive agents where the physical factors determine their attitude and process of decision making. However, this outlook was strongly criticized by geographers who favored a new school of thought known as environmental possibilism. The prominent scholars who supported the school of determinism were: Charles Darwin, Demolins, F. Rutzel, etc. Q??? With your friends, discuss why the philosophy of environmental determinism was severely criticized by the proponents of environmental possibilism. B. Environmental Possibilism  Is a philosophy that bases its view on the idea that the human beings are an influencing factor on the natural environment.  The school of possibilism was postulated by Febvre. 7  Supporters argue that human beings are masters of the environment and they can judge their benefits. They argued that there are no necessities but only possibilities.  Proponents of this view emphasize that two-way relationships exist between humans and the environment.  They state that people can influence the environment to enhance their way of life.  These geographers agree that the environment can potentially affect people’s activities, but they believe that we can use our knowledge and skills to regulate these effects. Nowadays, the school of possibilism is becoming widely accepted since it recognizes human’s ability to change its environment using the latest or better technologies. Example: Human beings have been using irrigation to turn barren lands of the deserts into agriculturally productive areas. C. The Quantitative Revolution The Quantitative Revolution has emerged as new theoretical approach, and the analytical method of inquiry to geographical research in the early 1950s. Socio-economic, physical, and political features and processes are spatially organized and ecologically related. As a result, a more abstract, theoretical approach to geographical research has emerged, and the analytical method of inquiry evolved this new approach. The Quantitative Revolution has used rigorous mathematical formulae borrowing from the physical sciences. This movement in geography is called the “Quantitative Revolution” Contributions of the quantitative revolution to the development of geography The quantitative revolution led to an increased use of statistical techniques. It emphasized multivariable analysis and the use of computers in geographical research. The methods adopted included various mathematical techniques that were more precise than the descriptive methods of regional geography. The quantitative revolution was a response to the crisis in the 1950’s. The crisis was the result of the challenges that geography faced during late 1940’s and early 1950’s. Some of the major challenges were:  The shutting down of many geography departments and courses. For example, the geography program at Harvard University was abolished in 1948. 8  The division between Human and Physical geography was continued demanding the autonomous subject hood of Human geography.  Geography was seen as solely descriptive and unscientific. As some argued, there was no explanation of why processes or phenomena occur in geography.  Geography was not useful for solving problems. Hence, it was seen as exclusively educational  Questions regarding the nature of geography persisted, for example, it was unclear to some people whether geography was a science, an art, a humanities subject or a social science.  The quantitative revolution was driven by the development of the computer and its ability to rapidly process data.  Quantitative geographers “went radical” and applied computers, statistics, and mathematical models to the study of geographers. Some of the techniques that became central to geography during the quantitative revolution were:  Descriptive statistics  Inferential statistics  Basic mathematical equations and models, such as gravity models Deterministic models e.g., Von Thünen’s and Weber’s location models  Statistical models, using concepts of probability  The revolution introduced a rapid change in the methodologies used in geographical research: a shift from descriptive geography to empirical law-making geography. D.The Emergence of Applied Geography Geography has been used since human beings appeared on earth. However, geographic knowledge had little chance of being used to solve geographic problems.  Applied Geography has emerged in the latter part of the 20th Century in geography:  Geography became a science that we can use /apply/ to solve socio-economic and political problems. Applied geography had its roots in the quantitative revolution. The emergence of applied geography increased the applicability of geographic knowledge in the following areas:  Today, many geographers work as:-  Urban planners, and GIS analysts,  Environmentalists, and cartographers, 9  Location analysts, and transportation planners,  Developing-nations specialists, and public-transportation planners,  Highway planners, and university-facility planners,  Transportation logisticians, and demographic analysts, etc. Thus, applied geography is the use of geographic analysis in private business, government, non-profit organizations etc. Applied geography solves problems and aids in decision making. 1.1.6. Relationship between Geography and other disciplines  Geography is an interdisciplinary subject.  It has strong relationships with various disciplines in both the natural and the social sciences. For instance,  Human geography is highly linked with social sciences, while  Physical geography is related to the natural sciences. Many academic disciplines are linked with geography. Among them are:  Biology relates with biogeography  Meteorology relates with climatology.  Geology links with geomorphology and soil geography.  Astronomy, Economics, Political science, History, Demography, Sociology, chemistry, and mathematics. 10 UNIT SUMMARY In this unit, we defined geography, discussed its scope, discussed its approaches, examined its major schools of thought and examined its relationship with other sciences. In summary: Geography is a systematic study of the spatial distribution of phenomena on the surface of the earth and of the two-way interaction between the natural and human environments. The scope of geography is very wide. It attempts to study many parts of the geosphere: the lithosphere, hydrosphere, atmosphere, anthroposphere and biosphere. Geographical studies are conducted based on two basic approaches, regional geography and systematic geography. The first studies all aspects of phenomena found in a region, while the latter investigates a single phenomenon globally. Environmental determinism and environmental possibilism are the two dominant philosophies that geographers use when they examine the relationship between humans and their environment. The philosophy of environmental determinism is related to the idea that the environment is the factor that determines peoples’ mode of living. In contrast, the possibilist philosophy emphasizes the two-way relationship between humans and the environment and the possibility for humans to change the environment. The emergence of the quantitative revolution in the 1950s and 1960s contributed a lot to the development of geography. It incorporated different statistical techniques in to geographical studies. The emergence of applied geography increased the practical applicability of geography. Applied geography solve, many different socio-economic and environmental problems. Geography is highly integrated with other disciplines. It shares a wide range of information with the social and natural sciences. REVIEW EXERCISE FOR UNIT I.True or False 1. The fact that deserts can be turned into agriculturally productive areas through irrigation supports the philosophy of environmental possibilism. 2. Geography is less practical in today’s world than it was before. 3. According to the determinist approach, human cannot change or influence the environment. 4. Systematic geography is the study of the general characteristic of a region. 5. The facts and principles of the natural sciences can be applied in geography 11 II.Matching: match the items given in the “A” with the statements given in the “B” column. A B A. Quantitative revolution 6. An ardent supporter of environmental B. Febvre determinism. 7. An ardent supporter of environmental C. Alexander Von Humboldt possibilism. D. Topical approach 8. A nomethic or empirical law- making geography E. Regional approach that occurred in the mid-20th C. 9. A geographic school largely concerned with the F. Demography structure of the ecological system and other G. Political geography social problems. H. Applied geography 10. A geographic approach that emphasizes various aspects of a defined spatial unit. I. Demolins 11. A geographic approach that singles out one or two elements and treats the distribution globally. 12. A branch of geography that deals with the dynamic and static aspects of population. 13. A branch of geography that deals with boundary, communication and activities between countries in relation to political power. 12 III.Multiple Choices 14. Which of the following opinions do you accept? A. The definition of geography is static. B. Geography is a discipline which does not have one single definition. C. Geography does not have any relationship with other disciplines. D. The definition of geography is not subject to any change. 15. Which of the following statements about geography is correct? A. Physical phenomena are evenly distributed over the surface of the earth. B. There is a one-way relationship between humans and their environments. C. All elements in the natural environment affect the way of life of its inhabitants. D. Human beings are not capable of modifying their environments. 16. The main theme of possibilism is: A. The two-way relationship between human and nature. B. Human beings are not capable of modifying their environments. C.Human society is a passive agent in the man-environment relationship. D. Human beings are always under the influence of their environment. 17. Which of the following reflects the deterministic outlook? A. Self-reliance B. People who live in cold climates are stronger and more courageous than those living in warm climates. C. Human is capable of modifying his environment. D. Analyses social structure in terms of human activities. IV Fill in the blank space 18. A German geographer who tried to show how people adapt to and are influenced by the environment was _________. 19. The sub field of geography that studies how plants and animals are distributed is called ________. 20. Part of the exosphere that represents the cultural landscape of the earth is_________. 21. A Greek scholar who coined the word ‘Geography’ for the first time was_________. 22.The use of geography for socio-economic and political problem solving and planning is known as _________. 13 UNIT TWO MAP READING AND INTERPRETATIONS 2.1 Definition and concepts Here is a simple definition:  A map is a simplified, diminished, plain representation of all or part of the earth’s surface as viewed from vertically above.  A map is a two-dimensional scaled representation of part or whole of the Earth surface on a flat body such as piece of paper, black board, wood or cloth.  Map reading encompasses a systematic identification of natural features like mountains, rivers, oceans, hills, rocks, etc. and manmade features like roads, railways, buildings, dam, etc. Here are the main features of maps: A map represents all or part of the earth’s surface. For example, a map might show a city such as Addis Ababa, the entire world, or a section of a garden. A map is a two-dimensional (plane) representation. For example, a map might be printed on a piece of paper. Maps show the earth’s surface as if it were seen from directly above. This view is called a bird’s-eye view. All maps are smaller than the area they represent. Maps are drawn to scale. In other words, the features shown on a map have the same relative proportions as they do in reality. For example, if one mountain’s diameter is twice as large as that of another mountain, the first mountain would be shown on a map as twice as large as the second. Maps are simplified representations. Most maps use generally accepted symbols to represent natural, artificial or cultural features of the area they represent. They also use conventional notations to provide background information such as the map’s title, date and scale. Discuss the following question and perform the following tasks in your group. 1. What does this mean: “A map is a two-dimensional plane representation”? 2. Compare and contrast maps and globes. 2.2 Uses of Maps The map is geography’s most important tool. It can present very simple information or highly detailed results from a complicated geographical investigation.  Maps are basically used for identifying locations, distance, area and direction. Location: With the help of a map it is possible to locate a place in reference to another place. For example, Ethiopia’s location can be expressed in terms of its neighboring countries, external land masses and water bodies. It is also possible to locate a place using astronomical grid references – parallels and meridians.  For example, the absolute location of Ethiopia is 3˚N-15˚N latitude and 33˚E-48˚E longitude. Distance: It is possible to calculate the distance between two or more places on a map. This is done by using the scale of the map.  For example, the air distance between Bahir Dar and Addis Ababa can be calculated by using a map of Ethiopia. Measuring distances as the scroll flies are carried out by the use of a ruler or straight edge in between the two locations, and then convert the measured distance into a real world distance using the map's scale. 14  For example, if we measured a distance of 10 cm on a map that had a scale of 1:10,000, we would multiply 10 (distance) by 10,000 (scale). Thus, the actual distance in the real world would be 100,000 cm which is equivalent to 1km distance interval. Area: The area of a place, a country, a region, a continent, a sub-continent or the whole world can be calculated from a map. This is done by measuring the length and the width of the given place on the map and by converting them to ground distances with the help of the scale of the map. Direction: A map can enable us to identify the direction and bearing of any place on the map. This is accomplished by referring to another place.  For example, a map of Ethiopia can help us to find the direction and bearing of Mekele by referring to Addis Ababa. In addition to these, maps can be used to:  Show the distribution of physical and human phenomena on the earth’s surface: distribution maps show the locations of phenomena on the earth’s surface. For example, we use distribution maps for Ethiopia to show the presence of human and animal populations, minerals, and vegetation. Similarly, we use distribution maps to show patterns of settlement, temperature, and health conditions.  Show surface configuration: topographic maps give information about variations in height on the earth’s surface. For example, they show heights and depths of valleys, plains and mountains.  Offer visual comparisons: because the earth’s surface is vast, it is difficult to compare places by direct observation. For example, it would be difficult to compare the distribution of landforms in Ethiopia and Kenya, even from an airplane. However, by offering us relatively small but accurate representations of the two countries, maps solve this problem completely.  Support development planning: Maps can provide planners with vital information to plan for the future. For example, maps can show current conditions and ongoing trends, and they can help us predict a nation’s socioeconomic conditions. Such information is invaluable to the country’s planners as they analyze possibilities and livelihoods and then prepare for the future. 2.3 Classification of maps Maps could be classified in terms of the following features:  Focus and level of detail (purpose) – the amount of information they present about their subjects, especially their ability to show small details.  Scale – the size of the area for which they give information and, therefore, the scope of the information that they give about these areas. Classification Based on Purpose: Maps can be classified as general-purpose or specific-purpose. A. General-Purpose Maps  A general-purpose map is a map that shows the features of a place in a relatively general way.  It provides a wide range of information about the place it represents.  General-purpose maps are not topical.  They tend to contain a little of many kinds of information at a relatively low level of detail. Topographic information of each kind in lesser detail. A topographic map is a good example of this. It can illustrate both physical and human-made features of the earth. B. Specific−Purpose Maps  Specific-purpose maps are often called thematic maps or topical maps.  We use these terms because specific-purpose maps emphasize on a single topic.  These maps show detailed information about their subjects.  Thematic maps can show almost any kind of information that varies from place to place, such as population distribution, rainfall and temperature patterns, and the distribution of types of soil or vegetation. Soil maps Vegetation maps 15 Climate maps Classification by Scale Scale is a ratio that shows the degree to which the area that is mapped has been reduced. Based on scale differences, maps can be classified into: Large-scale maps Medium-scale maps Small-scale maps Let us now consider each of these types of map in more detail.  Large-Scale Maps ≥ 1:50,000 What are large scale maps? Large-scale maps present small areas in detail with great accuracy. Large-scales are greater than or equal to 1:50,000. A large-scale map, such as the map of Addis Ababa, shows the city in considerable detail. Large scale maps present a relatively small area and show its features in considerable detail. For example, at a scale of 1:5,000, a map of a city can include many features – such as buildings. The map can also include many details, such as the bends in highways. Medium-Scale Maps 1:50,000 - 1:250,000 These are maps that are prepared with scales that range between 1:50,000 and 1:250,000. Medium-scale maps cover wider areas than large scale maps, but cover smaller areas than small-scale maps. They are also able to present more detailed information than small-scale maps but are less detailed than large-scale ones. Small-Scale Maps ≤ 1:250,000 Small-scale maps are those which are prepared with scales less than or equal to 1:250,000. These small–scale maps cover wider areas than large and medium scale maps. 2.4 Marginal and boarder information Maps are used to convey information. To read maps effectively, map users need information about the map. Such information is presented in the map’s margins and is known as marginal information. Marginal information includes:  Title of the map: Gives the map’s name. For example, “Soil Map” explains that the map presents information about soil.  Year of publication: identifies the year in which the map was published. Because this information tells you how old the map is, you might be able to judge whether the map’s contents are current or might be out of date.  Author: identifies the copyright owner of the map and indicates who (or what organization) has prepared the map.  Place of publication and publisher: tells where the map was published and identifies the organization that published the map.  Scale: This information indicates the extent to which the area that is represented in the map has been reduced.  Legend/Key: explains the meaning of the signs and symbols used in the map.  Type of projection: tells the kind of projection used in making the map.  Direction or orientation (North) arrow: Shows the north direction on the map.  The magnetic declination (variation): is the difference between Magnetic North and True North. This will be explained later in this unit. 16 2.5 Conventional Signs and symbols  Conventional signs and symbols are those signs and symbols that are used on maps through the agreement of all map-makers of the world. They are used to represent the same detail on a map in all the countries of the world.  Signs and symbols help the map reader to understand maps. Therefore, the map reader has to look first at the key or legend of the map. When you create a map, the symbols you select should satisfy the following requirements. They should be uniform throughout the map. They should be easy to read and understand. The space occupation, orientation and size of the symbols should be constant. Here are some of the symbols and conventional signs that are widely used and understood worldwide:  Cities and towns are indicated by dots or patches of shading;  Streams and bodies of water are often printed in blue; and  Political boundaries are shown by dot lines/solid lines. Figure 1 Conventional signs and symbols Map Scale The scale of a map is the ratio between the measurement of distance on the map and the corresponding measurement on the earth’s surface. For instance, the ratio of the map distance between two cities on a map and the actual distance between the two corresponding cities on the earth is the scale to which that map is drawn.  Map scale can be linear or areal.  Linear scale expresses the ratio of map distance to ground distance. It is the most common scale type.  Areal scale shows the relationship between map area and ground area. Areal scale is the square of linear scale. For example, if a map has a linear scale of 1 cm to 6 km, then the areal scale of the map is (1 cm)2 to (6 km)2, which means 1 cm2 to 36 km2. How to Find the Scale of a Map There are two ways of finding a map scale, if it is not given: A. By using the known distance between two points on the map 17 This method is used if the ground distance between two points or places shown on the map is given. Then use the following procedure to obtain the scale: i. Measure the distance between the two points on the map in centimeters. ii. Divide the obtained distance on the map by the ground distance to obtain the ratio between the two. This gives you the scale of the map. To understand this better see the following example. Let us say, if the straight-line distance between Addis Ababa and Mekele is 555 km. using the following figure, calculate the scale of the map: Figure 2. Map of Ethiopia Using the distance between Addis Ababa and Mekele: i.Measure the distance between Addis Ababa and Mekele by using a ruler approximately 3 cm. The given air distance between the two places is 555 km. ii. Find the ratio between the distance on map and the actual distance. This is the scale. 𝐃𝐢𝐬𝐭𝐚𝐧𝐜𝐞 𝐦𝐞𝐚𝐬𝐮𝐫𝐞𝐝 𝐨𝐧 𝐭𝐡𝐞 𝐦𝐚𝐩 𝐒𝐜𝐚𝐥𝐞 = 𝐆𝐫𝐨𝐮𝐧𝐝 𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞 3 cm to 555 km = 1 cm to 185 km = 1 : 18,500,000. B. By using latitudes In this method, the scale of the map can be obtained by using the values of latitudes. For example, let us calculate the scale of the above Figure by using the 5 o and 10o N latitude lines: 1. The degree difference between the two latitudes is 5o (10 o – 5o). 2. The distance that 5o represents is 555 km (111 km × 5). 3. The distance between the two latitudes on the map is approximately 3 cm. 4. The scale of the map is, therefore: 𝐃𝐢𝐬𝐭𝐚𝐧𝐜𝐞 𝐨𝐧 𝐭𝐡𝐞 𝐦𝐚𝐩 𝟑𝐂𝐦 𝐒𝐜𝐚𝐥𝐞 = = 𝟓𝟓𝟓𝐤𝐦 = 1cm to 185 = 1 : 18,500,000 𝐆𝐫𝐨𝐮𝐧𝐝 𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞  1o latitude is about 111 km This relationship is derived from the circumference of the earth – 40,000 km.  If 360o = 40,000 km 1o = ? 𝟏˚𝐱 𝟒𝟎𝟎𝟎𝟎𝐦𝐬 = = 111km 𝟑𝟔𝟎˚ 18 Measurements in maps [location, distance, area, direction] Some areas have regular or geometric shapes, such as rectangles, triangles, circles and squares. Others have irregular or non-geometric shapes. Measurements in maps area: This procedure is important for measuring areas on maps: 1. Measure the area of the feature on the map; 2. If the map scale is linear, convert it to areal; 3. Using the areal scale, convert the area on the map to actual ground area by using cross multiplication. Measuring Regular-Shaped Areas A regular shape is a geometrical shape such as a circle, triangle or square. If you are measuring an area with a regular shape, use the mathematical formula for its geometric shape. Then calculate the ground area by using the map’s areal scale. The following table gives you some of geometric formulae for calculating the areas of regular shapes. Table: Geometrical formula What is the ground area of the farmland? In the above sketch, the farm has a regular shape.  Measure the length and width of the rectangle on the map. Obtain its area on the map by multiplying the length by the width (area of rectangle = l × w ). This gives you the area of the farm on the map.  Change the linear scale, which is 1 cm to 2 km, into areal scale by squaring it. This gives you the areal scale : 1 cm2 to 4 km2.  Convert the map area into ground area by using cross multiplication. In other words, if 1 cm2 is to 4 km2, then what will 8 cm2 be? This gives you the ground area of the farm 32 km2. Without changing the given linear scale into areal scale, it is possible to calculate the area. 2cm x 2km 4 cm x 2km L= = 4km and W= = 8km 1cm 1cm Area = L x W; Area = 4km x 8km = 32km2 ; Therefore, the area of the farm land is 32 km2. 19 Measuring Irregular-Shaped Areas If the feature to be measured has an irregular shape, its area cannot be directly calculated by using mathematical formulae. In such cases, we can use the grid square method to measure the area of the lake on the map. Measurement of Direction Directions from one point to another or the bearing of one point from another can be given using two different sets of units. The traditional system uses the cardinal compass points north, east, and south, west and subdivisions of them. A modern, and more accurate, method gives the directions in degrees and fractions of degrees clockwise from north. The relationship between the two ways of giving directions is shown in following Figure. The following figure shows you how to determine directions and bearings on maps. The procedure involves the following steps. Example: To find the direction from point A to point B on the map ( the following figure); 1. Draw a line with a pencil joining points A and B on the map. 2. Through the point from which the bearing is required draw a pencil line parallel to true north as indicated by the meridians or the arrow indicating true north. 3. Using these two lines, set your protractor so that its centre is in point A and measure the angle between the true north line and the line A – B reading clock wise from north = 0o. 4. State the bearing either in compass directions or degrees clockwise from north. Figure: The measurement of direction Answer: i.The direction from A to B is 135o or point B bears 135o from A. ii. Point B is roughly South East of A or point B bears South East from A. Distance measurement Distance measurement on a straight course is quite simple compared to measurement of irregular features like river course or road. Measuring distances as the scroll flies are carried out by the use of a ruler or straight edge in between the two locations, and then convert the measured distance into a real world distance using the map's scale. For example, if we measured a distance of 10 cm on a map that had a scale of 1:10,000, we would multiply 10 (distance) by 10,000 (scale). Thus, the actual distance in the real world would be 100,000 cm which is equivalent to 1km distance interval. 2.6. Relief representation on maps How can we represent relief on maps? In order to read relief features from maps, you should first know how map –makers represent the uneven surface of the earth on a plane sheet of paper, i.e., on a map. There are different ways of showing relief on maps. These include:  Physiographic diagrams 20  Hachures  Layer coloring  Hill shading  Form lines  Contour Traditional Methods A. Physiographic Diagrams What is a physiographic diagram? Early map makers used to represent relief features by diagrammatic pictures known as physiographic diagrams. They show three-dimensional pictures of landscapes as viewed from the side or oblique direction. This method of showing relief is simple and easy to understand. However, it has the following disadvantages:  It shows the side and oblique view of the landscape, unlike the modern relief map that gives you an overhead view of an area.  Some geographic details of an area would be hidden from view behind the “backs” of the pictures of hills or mountains.  Exact heights and slopes of the land forms are not indicated  It lacks accuracy because it is drawn without scale. B. Hachures What are hachures? Hachures are short disconnected lines that represent slopes. They are drawn in the direction in which water flows. Originally they were used to represent mountains and valleys on simple sketch maps. Basically, hachures show the steepness of slopes. When slopes are steep, hachures are put close together. For gentle slopes, the hachures are spaced wide apart. In addition, hachures representing steep slopes are shorter than those representing gentle slopes. Figure: Hachured map This approach has significant limitations, such as: Flat areas are unshaded. Therefore, plateaus and plains can be confused. Hachures do not indicate height and exact gradients. They give only qualitative information. Hachures are laborious to draw and can be difficult to read and interpret. Nowadays, hachures are not used alone. Instead, they are used in combination with contour lines to show landforms like escarpments, depressions and craters. (contour lines are described in a later section of this unit). 21 C. Hill shading What is hill shading? What are some of the limitations of hill shading? Hill shading is also known as oblique illumination. It is a method of showing relief on a map, assuming an oblique light that illuminates the landscape from the northwest corner of the map. Hence the northwest-facing slopes are shaded lighter than are the east-facing and south-facing slopes. The steeper the slope is, the darker it is shaded. Hill shading offers a quick general impression of the land configuration that it represents. But still it has some limitations such as:  It does not give absolute altitude.  It fails to indicate clearly whether the ground is sloping upward or downward.  It fails to indicate whether the unshaded areas are low or high-level areas. Hence, plateaus and plains can be confused.  Detailed map information can be obscured by shading. In general, hill shading is now used in combination with spot heights and contours to overcome some of its drawbacks. D. Layer Coloring (Layer Tinting) What is layer coloring? It is a method of showing relief by using colors. The series of colors for showing different altitudes starts from sea level (see Figure). Identify the types of colors used to represent the different elevation zones in Figure. Elevation Zone Above 3000m 2501-3000m 1001-2500m 501-1000m 0-500m Water body Figure: Map with layer coloring Layer coloring has the following disadvantages:  Color shading does not indicate gradual changes in slopes.  The edges of the areas of different colors can suggest nonexistent physical boundaries.  Dark colors can obscure details in the areas that they overlie.  Some colors can create false impressions in the map reader’s mind. For example, green might suggest vegetation or a fertile area. E. Formlines 22 What are formlines? A formline is imaginary pecked or broken line joining points with the same approximate height on a map. Usually they are drawn on topographic maps to show where survey work is incomplete or poorly accomplished. Also, these lines are useful for showing sea depths. Formlines have the following limitations:  They are not drawn on a map at a fixed interval of altitude.  Although they represent the relief of an area, they provide little or no reference to sea level.  In many cases they are unnumbered.  They are usually drawn with broken lines. Modern Methods F. Contour Lines or Isohypses What are contour lines? How do contour lines differ from traditional methods of showing relief on maps? Contour lines are the most common and accurate way of showing relief on modern maps. A shoreline is a good example of a contour line. Properties of Contour Lines What are the main properties of contour lines? Why are contour lines more accurate than the traditional methods of showing relief on maps? General properties of contour lines Here are some important points about contour lines: i. Contour lines are imaginary lines used on a map to represent relief. Unlike the lines that represent rivers, boundaries or coast lines, contours do not really exist on the earth’s surface. The only contour line that exists both on the map and in the field is the sea level. ii.A set of contour lines is drawn at a fixed height interval. For example in the following figure, contour lines are drawn at 50-meter intervals. The difference in altitude between two successive contour lines is known as vertical interval (V. I.) or contour interval (C. I.). The V. I. helps us to find out the heights of unnumbered contour lines. iii. Contour lines cannot merge or cross one another on maps except at vertical cliffs, waterfalls or over hanging cliffs. For example, two or more contour lines run together and then separate to represent the cliff shown in the figure below. Figure: Contour lines showing a cliff The cliff in the preceding diagram is a vertical mountain wall. It rises from 100 meters to 150 meters. The crossing of contours occurs only in the case of an overhanging cliff. Usually contours representing a cave under an overhanging cliff are shown with pecked lines. 23 Figure: An overhanging cliff iv. Contour lines never branch. If you see branching lines on a map, they represent features such as rivers, roads, boundaries, etc. v.A contour line joins all points of the same altitude. For example, an altitude of 250 m will be on the 250 m contour line. The altitude of any point outside this line will be either greater or less than 250 meters. vi. Contour lines are always numbered in the direction towards which altitude increases. These numbers can be shown with or without breaking contour lines. Figure: Numbering of contours vii. Contour lines indicate the nature of slopes. When contour lines are far apart, they show gentle slopes. But when contour lines are close together, they show steep slopes. Figure: Contour-line spacing indicating slope steepness viii. Contour lines can be printed with different thicknesses on a map. This is especially helpful in mountainous areas where altitudes may vary considerably from summits to valley floors. In order to make the reading of contour maps easier, every fifth or tenth contour line is printed thicker than the rest. Such contour lines are called index contour lines, while the rest are called regular contour lines. ix. Contour lines can show different types of landforms, such as mountains, hills, plateaus, depressions, valleys, spurs, ridges, gorges, passes, plains, etc. Many of these relief features are readily recognized from the shapes of their contour lines. 24 Figure: Landforms represented both diagrammaticaly and by contour lines G. Different Methods of Showing Altitudes on Contour Maps What are the shortcomings of contour lines? How do you indicate the specific heights of hilltops, roads, railways, and towns? Contour lines show altitude and relief on modern maps. However, they do not show the specific heights of individual features such as mountain peaks, hilltops, valley floors, towers, towns, roads or railways. Such heights are indicated on maps, using the following methods: a) Spot heights  They are marked on the map with a dot followed by an altitude number:  They provide accurate altitudes for individual points, such as those along a road, on a mountain top, or between contour lines.  Unlike contour lines, spot heights do not give a good visual impression of the general relief.  They exist only on maps. b) Trigonometrical points  They exist both on maps and in the field.  They mostly mark features such as hilltops and mountain peaks. On the ground, the relevant feature is permanently marked with a pillar (concrete). On maps, they are shown with a small triangle enclosing a dot, followed by the exact altitude in meters. c) Benchmarks  They indicate precise heights along highways or railways.  They are shown on stones, bricks or bronze plates on walls of buildings and other convenient places  They are useful for road construction engineers and others who wish to know the precise altitude of a main transport network. d. Calculating Altitude: When the altitude of a point on a contour map is not shown by any of the above methods, it can be obtained by measurement and calculation, using the interpolation method. This can be done only if the given point is located between two contour lines. In order to find the altitude of point A in the figure, follow the procedures given below. i. Draw the shortest possible straight line that passes through point (A) and join the two contour lines adjacent to it. ii. Measure the length of this line: = 11 mm. 25 iii. Measure the distance on the map between the lower and upper contours up to point (A). They are 6 mm and 5 mm respectively. iv. Find the vertical interval between the two contour lines: = 100 m. v. Then determine the altitude of the point using the following formula: Where: d1 is distance of point A from the lower contour, d2 is distance of point A from the upper contour, D is distance between the upper and lower contours, VI is vertical interval, LC is the lower contour and, HC is the higher contour. Therefore, the altitude of point A is 754.55 meters. Figure: Altitudes shown on a contour map in different ways Scale 1:50, 000 Slopes and Gradients A. Slopes on Contour Maps What is slope? How can we determine the steepness of slopes on contour maps? What kinds of relations exist between V.I. and slope? Slope is the upward or downward inclination of a natural or artificial surface. It is a deviation of the surface from the horizontal. On a map, steepness of a slope depends on:  The distance between the contours drawn on the map. The closer the contours are, the steeper is the slope representation and vice versa (see Figure 1.24).  The vertical interval (V.I.) between two successive contours. The bigger the V.I, the steeper is the slope representation and vice versa. Types of Slopes How many types of slope do you know? Mention some of them and describe how you can identify them from contour maps. There are different types of slopes, which include: i) Even slope 26 An even slope has a constant gradient from the bottom to the top. Gradient is the degree or rate of a slope. You will learn more about gradient later in this unit. On a map of an even slope, the contour lines are evenly spaced throughout. For example, study the slope represented in the following Figure. Figure: Even slope ii. Concave Slope In a concave slope; the contour lines are widely spaced at the base and are close together at the top. In other words, a concave slope has a steep gradient at the top. The gradient becomes gentler towards the bottom (see the following Figure). Figure: Concave slope iii Convex Slope In a convex slope, the contour lines are close together at the base and widely spaced at the top. The slope has a steep gradient at the bottom that becomes gentler towards the top. (See the following Figure). Figure: Convex slope iv Terraced or Stepped Slope In a terraced or stepped slope, the contour lines are alternatively close together and far apart in a regular pattern. This means the gradient changes several times between the bottom and the top of the slope (see the following Figure). 27 Figure: Terraced slope v Escarpment An escarpment is the steep slope of a plateau, especially one where the plateau ends and the lowland starts. You can also identify other two more slopes on either side of a mountain ridge. One slope is steep and the other is gentle. The steep slope is called the scarp slope. The gentler slope is called the dip slope (see the following Figure). Figure: Dip and scarp slopes B. Gradient on Contour Maps What is gradient? What are the three common ways of expressing gradient? How do you determine the rate of change of slope between two points? Gradient (GR) is the degree or rate of change of slope or elevation between two points. It is calculated using altitude difference (vertical distance) and map distance (horizontal distance) between two points. Both AD and MD must be in the same unit of measurement. It can be expressed in any of these three different ways: AD 1. As a simple ratio: GR = MD Usually we express gradient as a percentage. This expression is the simplest to use, and it is relatively easy to calculate. 28 REVIEW EXERCISE FOR UNIT Activity Calculate the following: The distance on the map between Addis Ababa and Adama is about 10 cm with the scale of 1:1,000,000 on a certain map of Ethiopia. The average elevations of the two are about 2400 and 1700 meters, respectively. Determine the gradient in ratio, in percent and in degree. Short Answers: Give short answers to the following questions. 1.What is the basic difference between a contour line and a formline? 2.Indicate three shortcoming of hachures. 3.Define the term “cliff”. 4.Explain briefly the difference between spot heights and trigonometrical stations or points. 5. Things to Do: Answer the following questions by referring to Figure 1.37. 6. Find the approximate R.F. of the map _______. 7. Measure the direction (bearing) of: i. A from B ii. B from D iii. D from A 8. Between points C and E, calculate a.The field distance b.The gradient in; i) ratio ii) percent iii) degree 29 UNIT THREE THE PHYSICAL ENVIRONMENT OF THE EARTH (30 Hours) 3.1 Physical Environment of the World At the end of this section, you will be able to:  discuss the concept of universe  identify the position of the earth in the solar system  explain the origin of the earth  demonstrate the structure of the earth  describe the geological time scale and major geological events  realize the major geological events of Ethiopia  describe the concept of continental drift theory.  describe the characteristics of each type of rocks.  demonstrate major rock distribution in Ethiopia  state causes and impacts of soil degradation in Ethiopia. 3.1.1 The Earth in the Universe The universe is the totality of space and cosmos, in which everything is found. All heavenly bodies, including all stars, together with the sun, comets, meteors, planets and their satellites are found in the very vast space called the universe. A galaxy is a large group of stars. The universe contains many galaxies. The Milky Way is our galaxy. Within the Milky Way is our solar system. A solar system is a smaller group of heavenly bodies, which includes the sun at the center and the nine planets and their satellites and asteroids. 3.1.2 Forces That Change the Surface of the Earth A. INTERNAL FORCES Those forces that drive energy from the interior part of the earth are called internal forces. Internal forces form the ups and downs on the earth’s crust by breaking and bending (faulting and folding) it. Forces inside the crust cause folding, faulting (cracking), volcanism and earthquakes.  Folding Folding is one of the internal processes which occur when two forces act towards each other from opposing sides. Due to this force, rock layers are bent into folds. The process by which folds are formed due to compression is known as folding. There are large scale and small scale folds. Large-scale folds are found mainly along destructive plate boundaries. Types of folding: different types of folds are created, based on the nature of the forces applied on bedrock. If the fold is upward and convex, it is called anticline. If the fold is downward, it is called syncline. Fold Mountains  Fold Mountains are formed by crust which has been uplifted, and folded by compressional forces. They are formed when two plates move towards each other. The compressional force which is created as a result of this movement pushes sedimentary rocks upwards into a series of folds.  Fold Mountains are usually formed from sedimentary rocks and are usually found along the edges of continents. This is because the thickest deposits of sedimentary rock generally accumulated along the edges of continents.  There are two types of Fold Mountains:- Young fold mountains (10 to 25 million years of age, example, the Atlas, Rockies and the Himalayas) and Old fold mountains (over 200 million years of age, example, the Cape Range, the Urals in Russia and the Appalachians of the USA). 30 Many ranges of mountains have been formed by folding. The Andes, the Rocky mountains, the Alps, the Himalayas and the Australian Alps are some examples. The Atlas mountains in north west Africa and the Cape Range in South Africa were formed by folding. This process of mountain building is called orogeny.  Faulting Movements in the crust of the earth sometimes make cracks. These cracks are called faults. Faulting can be caused by either lateral or vertical forces, which can be either tensional or compressional. Tension causes a normal fault, and compression causes a reverse fault. Major features formed by faulting include rift valleys and block/Horst Mountains.  Rift Valleys What is rift valley? How are rift valleys and Block Mountains formed? A rift valley is a linear shaped lowland area between highlands or mountain ranges created by geologic rifts or faults. A rift valley is a valley formed by faulting. When two parallel faults occur on the surface of the earth, and when the land between the two faults sinks down, a rift valley is formed. The largest rift valley in the world is the East African Rift Valley. It extends from Syria to Mozambique, passing through the Red Sea, Eritrea, Ethiopia, Kenya, Tanzania, DR Congo, Rwanda and Burundi. The total length of the East African Rift Valley is about 7,200 km, of which 5,600 km is in Africa. The Ethiopian Rift Valley is a part of the East African Rift Valley. It extends from northeast to south west. Features found in the Rift Valley include active volcanoes, lakes, hot springs and fumaroles. Block (Horst) Mountains What is Block Mountain? How do block mountains form? Block Mountains are formed when land between two parallel faults is pushed upward due to pressure from inside the earth. If there are two parallel faults, the crustal block between them may either rise to produce a Horst (block) mountain, or fall, to produce a rift valley. Examples:  The Sierra Nevada Mountains in North America.  The Harz Mountains in Germany.  The Afar block mountain in Ethiopia.  The Ruwenzori in Africa.  Volcanism What is volcanic activity? What landforms are associated with volcanic activity? Volcanic activity is another internal force which changes the surface of the earth. It is caused by internal movements within the earth. Volcanism is the process by which magma; gases, water vapour, ashes and other solid materials are forced out to the surface. Inside the earth the temperature is very hot. This high temperature changes rocks into molten magma. When this magma reaches the surface, volcanic activity takes place. When the magma emerges on to the surface, it cools and hardens. It is then called lava. Magma reaches the earth’s surface through two kinds of holes. They are vents and fissures. Magma may force its way violently through a small hole called a vent. If lava emerges via a vent, it builds up into a volcano (cone-shaped mound), and if it emerges via a fissure, it builds up to form a lava plateau or lava flow. Magma may pour quietly through long cracks (fissures) onto the earth’s surface. If the magma flows to the surface through a vent, acrater is formed. Sometimes a volcano erupts very forcefully. When this happens, the top part of the volcano is blown away. This forms a large crater called a caldera. Water collects in the crater or in the caldera and forms a lake. We call this a crater lake or caldera lake. In Ethiopia there are many crater lakes such as Zuquala, Wonchi and Dendi. 31 If an eruption begins again in a caldera, a new small cone-shaped volcano is formed inside the caldera. These are known as caldera cones. Part of the magma may not reach the earth’s surface, and when this magma cools, solidifies and forms rocks inside the crust, features such as batholiths, lacoliths, sills and dikes, are formed. o A batholith is a very large mass of magma which accumulates in the crust. It is the largest structure. o A laccolith is a mushroom shaped body of intrusive igneous rock. Smaller than a batholith. o A dike is formed when magma solidifies in a vertical or near-vertical crack. o A sill is formed when magma solidifies horizontally or nearly horizontally along a bedding plane. Types of volcanoes Active volcano Erupts from time to time Erta’li, Fentale Dubbi and Has not erupted for a long time Dormant volcano but may erupt again in the Tatali and Dabbahu future Has not erupted within historic Mt. Zuquala, Ras Dashen Extinct volcano time and Batu Importance of volcanic eruptions:  Give us some ideas about the interior of the earth  Provide fertile soil.  Provide hot springs (with medical value).  Generate geothermal energy.  Help in the formation and concentration of minerals.  Help in the creation of new land.  Earthquake What is an earthquake? Why do earthquakes occur? Earthquakes are sudden movements in the earth’s crust. They are caused by internal movements deep down inside the earth. Earthquakes are frequently associated with faults. They take place along fault lines where the earth’s crust is weak. When an earthquake occurs, vibrations from the centre spread out in the form of waves in all directions. The point at which an earthquake originates is called the focus. The point on the earth’s surface immediately above the focus is called the epicentre. As the vibrations spin out from the centre, the damage they cause becomes less and less. The intensity of an earthquake is measured by an instrument called a seismometer, and is recorded on a seismograph. It records the vibrations produced by an earthquake. The scale which gives the magnitude is called the Richter scale. It ranges from 0 to 9. Each number of this scale indicates a tremor that is ten times stronger than the next lower number. An earthquake with a magnitude of 4.0 is ten times stronger than one that measures 3.0. Readings of 7.0 or higher indicate a strong or major earthquake. The strongest ever recorded earthquake was the Valdivia earthquake in Chile that occurred on May 22, 1960 (9.5 on the Richter scale). Table 2.2: Richter scale values and the corresponding magnitude of earthquakes The Richter Scale Effects < 3.5 only by instruments (seismometers) 3.5 – 4.8 Feels like a lorry passing 4.9 – 5.4 Loose things fall 5.5 – 6.1 Walls crack 6.2 – 6.9 Chimneys fall, some buildings collapse 7.0 – 7.3 Many buildings fall, landslides 7.4 – 8.1 Most buildings and bridges are destroyed > 8.1 Total destruction 32 In addition to destruction of life and property, an earthquake causes:  displacement of parts of the earth’s crust vertically or laterally.  landslides and deep cracks in surface rocks.  the devastation of cities, fires and diseases.  the rise or lowering of the sea floor. About 80% of all earthquakes occur in three regions. They are  Around the Pacific Ocean zone. The largest earthquake and volcano zone lies along the edges of the Pacific Ocean. This zone is known as the Pacific Ring of Fire.  Across Southern Europe and Southern Asia.  The west-coast areas of North and South America. The two most recent earthquakes in Ethiopia measuring more than 5 on the Richter Scale occurred:  July 14, 1960, near Lake Shalla with a magnitude of 6 on the Richte Scale.  June 2, 1961, in Karakore. B. EXTERNAL FORCES  Weathering What is weathering? What is the effect of weathering on landforms? External forces can lower the level of the land by washing it away, and this process is called denudation. They also can raise the level of the land by deposition. Denudation consists of weathering and erosion. Weathering includes disintegration (physical weathering), which breaks rocks into smaller pieces and decomposition (chemical weathering), which forms new substances. o Physical (Mechanical) Weathering What is physical weathering? What are the main agents of physical weathering? Physical weathering breaks the rocks into smaller pieces. Its main agents (causes) are temperature changes, frost action and the action of plants and animals. The effects of temperature changes: The temperature variation between day and night causes rock to expand and to contract. This process causes cracks to develop. In time, the cracked layer peels off and falls to the ground. This process is called exfoliation. The effects of frost action: Due to frost action, rock breaks up into pieces and these fragments accumulate around the lower slopes of the rock. This material is called scree. Frost action is very common in the winter season in the temperate zone and in some high mountains all year round. The effects of plant and animal action: Plants and animals also cause weathering. For example, seeds may fall in cracks of rocks. If water collects there, it forms suitable conditions for the seeds to germinate and grow. As plants develop their roots may push the rock apart. Some animals burrow, and this also helps to break up rocks. Chemical Weathering (Decomposition) What process is important in chemical weathering? What are main agents of chemical weathering? Chemical weathering is a process that forms new substances, and it is affected by the minerals in the rock. Its main agents are rain action and plant and animal actions. As rain water passes through the atmosphere, it takes in carbon dioxide (CO2) and forms a weak carbonic acid. When this acid water comes into contact with rock, it begins to dissolve minerals in the rock. The rate at which rock dissolves depends on the type of rock. Limestone, for example, dissolves very quickly. This process is known as carbonation. H2O + CO2 ⇒ carbonic acid ⇒ dissolves and erodes limestone and forms caves. 33 Example: Sofomer Cave along the River Weiyb in Bale. In underground rivers, seeping rain water continues to dissolve the limestone beneath the surface, gradually forming passages and caves. These caves contain features such as stalactites, stalagmites and pillars.  A stalactite is a limestone column that hangs down from the ceiling of the cave.  A stalagmite is a limestone column that builds upwards from the floor of the cave.  A pillar is formed when a stalactite and a stalagmite join together. When rain water dissolves oxygen and reacts with iron in rocks, the rocks become rusty. Pollution in towns and cities increases chemical weathering. How do plants and animals act as agents of chemical weathering? Plants absorb minerals, and decaying vegetation produces organic acid, which causes a further breakdown of minerals. Bacteria in the presence of water break down certain minerals in the soil. Leaching is a major soil-forming process. It occurs when substances are dissolved in water that percolates through soil. Such substances include soluble chemicals that move out of biological tissues into soil - for example, rainfall causes potassium and other ions to be lost by foliage.  Erosion What is erosion? What are the major agents of erosion? What are the major types of erosion? What are the characteristics of the agents of erosion? Erosion is the transporting of weathered material by various natural forces such as moving water, wind and moving ice. Erosion occurs when particles of rock or soil are:  washed away by a river  removed by waves of the sea  crushed under a glacier  blown away by the wind Erosion by Running Water How does running water cause erosion? What processes are included in erosion? Rivers are the most important of all natural agents which help in shaping the earth’s surface. The work of running water includes eroding, transporting and depositing eroded material. There are three types of running water erosion: 1. Sheet erosion: occurs when surface water moves in a wide flow. 2. Rill erosion: occurs when surface water cuts relatively small channels. 3. Gully erosion: occurs when floods cut deep wide gorges. The course of a river, from its source to its mouth, can be divided into 3 stages. The action of the river is different in these three parts. The stages are upper course, middle course and lower course. 34 Fig: The three stages of a river Upper Course In this stage the river water is usually small in volume. As the river flows very fast down steep-slopes, a V-shape valley, waterfalls and deep gorges are formed. The fast flow of the river causes vertical erosion and destruction. The V-shape valley has steep sides and a narrow floor. The fast flowing river cuts down deeply into the land. Waterfalls are caused by sudden drops in the level of rivers. Waterfalls are formed when water flows over hard rock which cannot be eroded easily, while soft rocks are easily eroded. The hard rock produces an overhang, and the water flows over it as a waterfall. The Middle Course During a river’s middle course, the river valley becomes wider and larger. The river may receive waters of many tributaries, which increase the volume of water. Wide-floored valleys with gentle slopping sides are the main features of the middle course of the river. Instead of taking the most direct course possible, the river begins to meander. Meanders are pronounced curves in the course of a river. The Lower Course The river flows fast, meandering over wide plains, and makes widespread deposition. The load is so large that deposition occurs. Flat floodplains, big meanders, levees, ox-bow lakes and deltas are the main features of this course. 35 Fig: Features of the lower course of a river  Floodplains are broad flat areas which border with the lower course of a river and are sometimes flooded by the river. They are covered with fertile alluvial soils which are deposited by the river when flooding.  Levees are narrow ridges of alluvial deposits found along the bank of a river.  Ox-bow lakes are crescent-moon shaped lakes created due to meanders that have been abandoned. They are formed when meanders are cut off from the main river channel.  Deltas are usually triangular areas of land which are usually formed at the mouth of rivers. Erosion and Deposition by Sea Waves What are coastal landform features produced by wave erosion? Waves are formed when wind moves over the surface of the sea. This causes the particles of water to move in a circular motion, which forms a wave. This movement of water in the sea clashes against coastal lands and picks up rock particles and throws them into the sea as sediments. The work of the sea along the coast includes erosion, transportation and deposition. Some of these features formed along the shoreline are beaches, spits and lagoons.  Beach is a strip of land along the sea coast covered with various types of sediment.  A Spit is a narrow ridge of sand or shingle. It projects into the sea but is attached to the land at one end.  Lagoon is an area of saltwater separated from the sea by loose sandbanks. Wind Erosion and Deposition What is the most active agent of erosion in desert regions? What is the most common type of wind deposit? Wind erosion is common in desert and semi-desert areas. Wind erosion and deposition form different landforms such as sand dunes, barchans and loess deposits.  Sand dune is a small hill of sand formed by the action of the wind.  Barchan is a sand hill that has a crescent-moon shape.  Loess deposit is a deposition of fertile soil in the desert by wind. 3.1.3. Weather and Climate At the end of this section, you will be able to: 36 explain the meaning of atmosphere; discuss the composition and layers of the earth’s atmosphere; explain weather and climate; express the concept of temperature; appraise the variation of temperature; demonstrate how to measure and record temperature data; compute normal temperature lapse rate; interpret temperature data; explain the formation of rain; discuss the types of rainfall; relate the various roof slopes of houses in various climatic regions to the respective types of rainfall; practice measuring and recording rainfall data; differentiate types of winds (local, monsoon and planetary winds, including cyclones and anticyclones); relate direction and deflection of winds to the earth’s rotation; interpret wind speed and direction from wind gradient map; explain how conditions of wind affect structures of buildings and crop production; Identify types of atmospheric pressure; relate atmospheric pressure with temperature and altitude; demonstrate the pressure belts of the world: develop the skills of measuring and recording atmospheric pressure; analyze the position of the sun at various latitudes at noon time of Dec. 22/June 21; examine the impact of latitude on temperature; justify the effect of altitude on the characteristics of temperature, rainfall and air pressure; compare and contrast the condition of rainfall and temperature between places of coastal and interior areas; express the meaning and types of ocean current; identify the impacts of ocean currents; recognize the effects of ocean currents on temperature and rainfall on land surfaces; Earth and Atmosphere What is atmosphere? How do you explain the importance of atmosphere for human beings or for all life forms? The air that surrounds the earth is called the atmosphere. It is an envelope of transparent colorless, tasteless and odorless gases found above the earth’s surface. Composition of the Atmosphere: The earth’s atmosphere is a mixture of gases, suspended dust particles and condensed moisture droplets which are collectively known as aerosols. The gases are different in their volume Table: Gases of Earth’s atmosphere Table 2.4: Atmosphere layers and their characters 37 Meaning of Weather and Climate What is the condition of the atmosphere today? What is weather? What is climate? How is climate different from weather?  Weather is the condition of the atmosphere over a short period of time. Weather includes daily changes in precipitation, air pressure, temperature, wind, etc. Weather refers to atmospheric conditions in a given location. What is the weather like in your locality today?  Climate is the average of all weather conditions of an area over a long period of time. These conditions include average temperature, air pressure, humidity, and days of sunshine for a period of 30 years. Climate tells us what it is usually like in the place where we live. Major Elements of Weather and Climate The major elements of weather and climate are temperature, rainfall, winds, air pressure, clouds, etc.  Temperature What is temperature? Temperature is the amount of hotness or coldness of an object. The sun is the primary heat source for the earth and its atmosphere. The sun’s energy is called insolation or solar radiation, and this turns into heat energy at the earth’s surface. How is energy transferred in the atmosphere? 38 Not all the energy that originates from the sun reaches the earth’s surface  Heat transfer takes place in three ways. These are  Radiation  Conduction  Convection Radiation is the transfer of energy from one body to another by means of electromagnetic waves. Energy transmitted from the sun reaches the earth’s surface through the process of radiation. Electromagnetic waves usually travel through empty space. When these electromagnetic waves come in contact with an object, they transfer the heat to that object. The sun warms the earth through radiation of electromagnetic waves. Conduction refers to the transfer of heat through molecular contacts within and between bodies. Molecules are always in motion. The process of conduction is more important in solids. Air and water are poor conductors of heat. Convection is the transfer of heat due to differences in density. As gas or liquid either warms and rises or cools and falls, it creates convection currents. Convection is the method by which heat moves through gases or liquids. As gas or liquid is heated, it warms, expands and rises because it becomes less dense. When the gas or liquid cools it becomes dense and falls. Heat gained through radiation or conduction usually transfers by convection. Measuring and Recording Air Temperature What is the instrument that is used to measure temperatures? Explain how air temperature is measured and recorded? We measure temperature with thermometer. There are two types of thermometers: maximum and minimum thermometers. A maximum thermometer is a mercury-in-glass thermometer that has a constriction near the bulb end. When the temperature of air rises, the mercury in the thermometer expands and forces its way into the stem past this constriction. But when the bulb cools, none of the mercury above the constriction moves back into the bulb. Therefore, the length of the mercury in the stem remains the same. The end of the mercury thread, which is the farthest from the bulb, registers the highest temperature reached in a day.  The freezing point of mercury is –38.83oC, and the boiling point is 356.73oC  Alcohol freezes at a temperature of negative one hundred thirty degree Celsius (–130oC) A minimum thermometer has alcohol as its liquid, and it sets a metal index. When the temperature falls, the alcohol column drags the index towards the bulb end. When the temperature rises, the alcohol column expands and runs past the index without disturbing it. Thus, the end of the index, moves the farthest from the bulb and gives the lowest temperature attained in a day. Alcohol thermometers may be used to measure temperatures from -130oC (freezing point of a

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