Grade 9 Geography PDF - Ethiopia

Unit One GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA  Grade 9 | Geography Unit Outcomes After completing this unit, you will be able to: recognize the concept, scope and branches of geography; express the basic land features of the physical envi...

Unit One GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA  Grade 9 | Geography Unit Outcomes After completing this unit, you will be able to: recognize the concept, scope and branches of geography; express the basic land features of the physical environment; describe the absolute and relative location of Ethiopia; analyze the effects of shape and size of Ethiopia on its sociocultural, political and economic condition; explain geologic processes that shaped the land surface of Ethiopia; and describe the different landforms of Ethiopia. Main Contents 1.1 GEOGRAPHY: MEANING, SCOPE AND BRANCH 1.2 LOCATION, SIZE, AND SHAPE OF ETHIOPIA 1.3 GEOLOGICAL HISTORY OF ETHIOPIA Unit Summary Review Exercise 1.1 GEOGRAPHY: MEANING, SCOPE AND BRANCHES At the end of this section, you will be able to: define geography as a subject; describe the scope of geography; and identify the branches of geography. KEY TERMS մ Geography մ Physical geography մ Human geography մ Spatial 2  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA 1.1.1 Meaning of Geography What is geography? Do you think geography has a single universally accepted definition? If not, why? The term “Geography” first appeared in history at the time when the Greek civilization reached its peak. They defined geography for the first time by combining two words of Greek origin namely: Geo and Graphos. → Geo – which means earth → Graphos – which means writing Eratosthenes, a famous Greek Philosopher (276-194 B.C) coined the term Geography and defined it as “the field of study that deals with the description of the earth”. Now this definition seems very general when we compare it to the scope of current geography. A number of definitions have been given by different scholars of the nineteenth and twentieth centuries. These definitions relate to geography’s current concerns, interests and focus. Here are some of the most important definitions that scholars have proposed: Þ Eratosthenes (276-196 BC) – Geography is the description of the earth. Þ Alexander Von Humboldt (1769-1859) - Geography is a synthesizing discipline to connect the general with the particular through measurement, mapping, and a regional emphasis. Þ Concise Oxford Dictionary (1964) - Geography is the science of the earth’s surfaces. Þ 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. Þ 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 have read above, each of these definitions includes the idea that geography studies the earth. Most of them specify the surface of the earth. 3  Grade 9 | Geography It is difficult to forward a definition acceptable to all geographers at all times and places because of the dynamic nature of the discipline and the changes in its scope and method of study. However, the following may be widely accepted definitions by most scholars. Geography is the scientific study of the Earth that describes and analyses spatial and temporal variations of physical, biological and human phenomena, and their interrelationships and dynamism over the surface of the Earth. 1.1.2 The Scope of Geography What does the word scope mean? What is the scope of geography? Scope refers to the content (how broad or narrow) of the field of study of a given discipline, in this case geography. The scope of Geography is very wide. As the scope is dynamic, it often changes as discoveries and ideas enter the field. Geography studies a great many physical and human features of the world. Its focus includes their causes, effects, and interactions. As a result, the subjects that geography examines include features in the hydrosphere, atmosphere, lithosphere, biosphere and anthroposphere. Geography as a field of study is also concerned with the economic, social, political and ecological problems that you hear every day. It is also concerned with modern technology, such as computers, Global Positioning System (GPS) and Geographic Information System (GIS) to analyze information and draw conclusion with accuracy. NOTE Þ Hydrosphere – it includes all the bodies of water, i.e., oceans, rivers, lakes and others. Þ Biosphere – refers to all living organisms in and on the earth’s surface. Þ Atmosphere – it includes all aspects of air composition surrounding our planet. Þ Lithosphere – it is the solid layer of rocks that covers the entire surface of the planet. Þ Anthroposphere – it is the part of the environment that is made or modified by humans. 4  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA Did you notice how wide the scope of geography is? Do you understand the extent of its scope? It is true that geography has a very wide scope. However, this does not mean its scope is limitless. The major areas that geography focuses on are: Þ the earth, its position in the universe and its movements; Þ the different physical features that constitute the earth’s surface, the forces that cause them, their variations from place to place and their changes over time; Þ the different relationships between human beings and their natural environment. Also, the interdependence and the impact that each has on the other; Þ the conditions of the lower part of the atmosphere and the subsequent weather and climatic conditions, together with their spatial distribution and variation; Þ the materials that make up the earth and its diverse landforms; and Þ the major economic activities of humans and the impacts on the environment. Therefore, geography deals with an enormous range of phenomena ranging from physical and biotic to human environment. It is possible to conclude that although wide in its scope, geography has certain areas that it focuses upon. Hence, geography is a holistic discipline of knowledge and research (academics). 1.1.3 Branches of Geography What are the two branches of geography? Can you list some of the fields of geography that fall into each of the two branches? You have studied the definition of geography, and you have considered its scope. Next, you will learn about the main parts of geography and its sub-branches. The two main parts are: Þ physical geography; and Þ human geography 5  Grade 9 | Geography A. Physical Geography What does physical geography study? Do you know the sub-branches of physical geography? Physical geography studies the distribution of the natural features of the world, such as climate, landforms, soil, vegetation, surface drainage systems, water resources and animals. This branch of geography also considers the causes, effects and interactions of these features. Physical geography is further sub-divided into more specialized fields of study as follows: Physical geography Geomorphology Climatology Biogeography Oceanography Soil geography Phytogeography Zoogeography Geomorphology: it is the study of landforms, their distribution, origin and the force that change them. Climatology: studies factors that create the climate and examines the variation and distribution of climate and related causes and effects. Biogeography:generally speaking, it deals with the distribution of plants and animals. One part of biogeography deals with patterns of vegetation growth in relation to climate, soil and human activities and it is known as phytogeography. There is also another part of biogeography that studies why certain animals live in one region and not in other. In addition, it investigates the migration of animals and the factors that affect their movements. This area of study is called zoogeography. 6  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA Oceanography: studies the location, causes and effects of ocean currents, waves and tides. It also investigates the ocean floor. Soil geography: studies the distribution of various types of soils throughout the world. Soil geography studies how different kinds of soil influence the type and amount of crops produced in an area. It also examines how soils are affected by the agricultural activities practiced in an area. B. Human Geography What does human geography study? Do you know the sub-branches of human geography? Human geography studies the distribution and influence of human aspects of our world, including cultures, population settlement, economic activities and political systems. This branch of geography is sub-divided into the following specialized fields of study. Human Geography Cultural Population Economic Political Urban Historical Geography Geography Geography Geography Geography Geography Cultural geography: it examines 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: it is concerned with population distribution and factors affecting it. It also deals with birth and death rates, population structure, population movements, house hold size and other related statistical data. Economic geography: it studies production, consumption, exchange, the spatial distribution of goods, services and factors affecting them. Political geography: it deals with the distribution of political systems and the 7  Grade 9 | Geography ways people use them to exercise power and make decisions. It also studies topics such as changes in political boundaries, problems of political instability and patterns of voting. Urban geography: it studies the development and characteristics of towns, cities and other urban centers. It also investigates where different groups live within a city; why and where slums develop. Historical geography: it is the study of the geography of the past and how places, regions and patterns of human activity have changed over time. Activity 1.1 Discuss the following questions in small groups. 1. Geography studies the spatial distribution of phenomena on the earth’s surface on one hand and the two-way interactions and interdependences between humankind and the environment on the other. Do you agree or disagree to this statement? Why? 2. Some people say geography is concerned only with the study of place names. Do you agree or disagree to such idea? Why? 3. Do you think that the scope of geography is limitless? Why or why not? 4. What are the major areas of the study of geography? 8  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA 1.2 LOCATION, SIZE AND SHAPE OF ETHIOPIA At the end of this section, you will be able to: describe the absolute and relative location of Ethiopia; and discuss the effects of size and shape of Ethiopia on its sociocultural, political and economic contition. KEY TERMS մ Absolute location մ Latitude մ Compact shape մ Longitude մ Elongated shape մ Relative location մ Strategic location մ Vicinal location 1.2.1 Location of Ethiopia Why is the location of things important in geography? What locational significance does Ethiopia have as a country that is in the Horn and near the Red sea route? A location is a place where a particular point or object exists. In spatial distribution, every place has its own particular location in relation to its surroundings. In geography, the term location is a much more abstract concept than what an ordinary person knows. This important term is usually expressed in two ways: relative location and absolute location. A. Relative Location of Ethiopia Can you identify the relative location of your school or residence? Relative location refers to the position of a place in relation to the location of other geographic features. Relative location can be expressed in the following two ways; namely; vicinal location and geological location. Vicinal location shows the location of a country in relation to neighboring countries (Table. 1.1), while the strategic also 9  Grade 9 | Geography known as natural location describes a country’s location in reference to water bodies and landmasses. i. Vicinal Location of Ethiopia Ethiopia is a landlocked country that is surrounded by six neighboring countries (see Fig 1.1). Each country shares different lengths of Ethiopia’s borderlines. The total length of Ethiopia’s boundary line is 5,260 km. Table 1.1: Ethiopia’s Boundary Line length as Shared with Neighboring Countries SN Bordering Shared Boundary Ethiopia is found; Countries Length in Km 1 Djibouti 310 West of Djibouti 2 Eritrea 840 South of Eritrea 3 Kenya 760 North of Kenya 4 Somalia 1,600 West and Northwest of Somalia 5 Sudan 744 East and Southeast of Sudan 6 South Sudan 1,006 Northeast of South Sudan Total 5,260 Table 1.1 indicates that Ethiopia shares the longest length of boundary line with Somalia while the Republic of Djibouti shares the smallest boundary line length. Figure 1.1: Relative Location of Ethiopia 10  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA ii. Strategic Location of Ethiopia Strategic location is also called natural or global location. Consequently, Ethiopia’s strategical location can be described in the following ways. It is found: Þ in northeastern (Horn) Africa; Þ to the southwest of the Asian continent; Þ in the Nile Basin; Þ to the south of Europe; Þ to the northwest of the Indian Ocean; Þ to the southwest of the Red Sea; and Þ to the south of the Mediterranean Sea. B. Absolute or Astronomical Location of Ethiopia How do we know the exact position of Ethiopia on the earth’s surface? Can you describe the absolute location of Ethiopia? Absolute location is expressed as a geographical extent, in terms of latitudes and longitudes. The absolute location of Ethiopia is expressed as follows. Ethiopia is located between 3oN – 15oN latitudes and 33oE– 48oE longitudes As a result, Ethiopia’s extreme points lie at: Þ the Northern tip of Tigray in the north; Þ Moyalle in the south (Borena); Þ Akobo in the west (Gambella) and Þ the tip of Ogaden in the east (Ogaden) ( see Fig.1.2). Figure 1.2: Absolute Location of Ethiopia 11  Grade 9 | Geography 1.2.2 Size of Ethiopia How big is Ethiopia areally and what are the effects of its size? Ethiopia is the tenth largest country in Africa, with a total area of 1,106,000 square kilometers. It contains about 0.7 percent of the world’s land area and about 3.6 percent of Africa’s land mass. Table 1.2: Comparison of Ethiopia’s Areal Size with its Neighbors Country Total area (in sq.kms) Rank Size in comparison to Ethiopia Ethiopia 1,106,000 2 − Sudan 1,849,233 1 1.01 times bigger Somalia 637,661 3 1.73 times smaller Kenya 580,000 5 1.91 times smaller Eritrea 118,000 6 9.42 times smaller Djibouti 23,200 7 Almost 50 times smaller South Sudan 631,928 4 1.75 times smaller Source: CSA, 2012 NOTE The Horn of Africa takes its name from the horn-shaped land formation that forms the easternmost point of the African continent, projecting into the Indian Ocean south of the Arabian Peninsula. Ethiopia is the largest country in the Horn. This status in size, in combination with its status of having a large population, confers many advantages to Ethiopia in the Horn area. What advantages and disadvantages does Ethiopia’s large size offer the country? Advantages: Ethiopia’s large size lets it: Þ enjoy diverse agro-ecological zones, resulting in a wide variety of fauna and flora; 12  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA Þ possess a large amount of arable land; Þ have a great variety of mineral resources; and Þ be the home of diverse ethnic groups. Disadvantages: Its large size forces Ethiopia to: Þ require expensive administrative expenditure; Þ have a large army to protect its sovereignty; Þ require great financial power to construct infrastructural facilities; and Þ face challenges for effective administration and socio-economic integration. 1.2.3 Shape of Ethiopia Look at the shape of Ethiopia and the neighboring countries. Does Ethiopia have similar shape with its neighboring countries? Can you identify the shape of each neighboring countries? Countries of Africa and the world at large vary not only in location and size but also in shape. Some countries have nearly circular (compact) shapes, others have elongated (linear) shapes, and still others have truncated (shortened) shapes. These shapes have implications on the administrative, defense and economic integration, both within the country and with respect to outside areas. When you compare the shape of Ethiopia with the other countries, you find that Ethiopia has more or less compact (circular) shape. Its shape is considered to be compact or essentially circular because the extreme north-south and east-west spans of the country cover comparable distances. You can easily see this approximate circularity in your school atlases and wall maps. There are three theoretical indicators of the compactness of an area: Þ the boundary - circumference ratio (B/C); Þ the area - boundary ratio (A/B); and Þ the actual area - area of the inscribing circle (A/A’). 13  Grade 9 | Geography NOTE Each of these theoretical assumptions is based on a value of 1 as indicating a perfectly compact shape except A/B ratio. They consider 0.5 –1.5 values as deviating only slightly from circular/compact and therefore indicating approximate compactness. In contrast, smaller values indicate greater divergence from compactness, especially as they approach zero (0). These small values reflect tendencies to elongation or truncation. On the other hand, A/B ratio compares the total area of a country under consideration with the total boundary length of the same country. The larger the areal size per unit boundary length is, the more compact the country is. For example, let’s use the boundary-circumference ratio to measure Ethiopia’s degree of compactness or index of compactness. In the ratio, circumference is based on the assumption of a circle having equal area with the country under consideration. Boundary length of the country Index of compactness using B/C ratio = Circumference of the circle The formula to find the circumference of a circle having equal areal size as the country under consideration is 2πr (π=3.14 ). The value of radius (r) is not given, and it should be computed. It is going to be calculated taking an area of a circle that is assumed to have equal areal size as the country under consideration.. Thus, area of the circle is calculated taking the following formula (i.e. A=πr2). Example: The B/C ratio of Ethiopia can be calculated as follows:  The total boundary length of Ethiopia: = 5260Kms  Circumference of a circle having an area similar to area of Ethiopia (=1,106,000Km2). Solution C=2πr , The value of π is 3.14, while the value of “r” is derived from the circle whose area is equal to Ethiopia’s area (i.e., 1,106,000Km2). πr2 = 1,106,000Km r2= 352,229.3 Hence, r= 593.5 Kms 14  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA Therefore, C= 2πr Circumference of area of Ethiopia (if it were circle) =2 x 3.14 x 593.5 = 3727.18 B/C ratio of Ethiopia = 5260/3727.18 = 1.411 This value implies that the shape of Ethiopia has a deviation of 41% from the assumed theoretical circular shape it ought to have. The compact shape has militaristic advantage as stated earlier. This can be well explained by considering an area and borderline length ratio. The index of compactness using A/B ratio for Ethiopia is indicated hereunder. A (Area) 1, 106, 000km = 5260 = 210 B (Border line) What does this ratio imply? Þ It implies that if 1 km borderline is safeguarded by national army, 210 km2 of the hinterland will become free from the assault of an enemy. Another way of estimating the compactness of shape of any country is considering the ratio of area of the country to the area of the smallest inscribing circle. In the ratio, area the circle is based on the assumption of smallest inscribing circle that touches the north, south, east and west boundaries of Ethiopia described earlier in the “Absolute Location” section. The ratio of actual area to the area of the smallest inscribing circle (A/A’) for Ethiopia can be calculated using the following formula: Actual area of the country Area of the inscribing circle N.B. Lower value near 0 indicates elongation and a higher value near 1 suggests more compactness. 15  Grade 9 | Geography Activity 1.2 Answer the following questions 1. Use a world map or atlas and identify places that are in the following positions: 3oN – 15oN & 33oE– 48oE 2. In small groups, discuss the effects of the location of Ethiopia on the global socio- economic and political dynamics. 1.3 GEOLOGICAL HISTORY OF ETHIOPIA At the end of this section, you will be able to: explain the geological history of Ethiopia; distinguish the geological processes that result in the current landform of Ethiopia; and describe major landforms of Ethiopia. KEY TERMS մ Endogenic force մ Exogenic force մ Regression մ Epeirogenic մ Geology մ Relief մ Epoch մ Orogenic մ Transgression մ Era մ Period 1.3.1 The Geological Processes in Ethiopia Which geological era is significant regarding the formation of the various landforms in Ethiopia? The geological history of Ethiopia is part of the geological processes that acted within and upon the earth’s surface for many millions of years in the past. To describe 16  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA the geology and history of life on Earth, scientists have developed the geological time scale. The geological time scale measures time on a scale involving four major geological eras. Each era is divided into periods, the periods into epochs, epochs into years and years into major occurrences. Each geological era is distinguished from the others based on grounds of the following three characteristics: Þ the relative positions of the continents; Þ the character of the prevailing climate; and Þ the predominant lifeform (plants and animals). Summary of Major Geological Events in the Horn Let’s begin by considering the different geological eras and then study the events that took place in those eras. Here are the geological eras, in chronological order.  The Precambrian Era – the oldest era (from 4.5 billion years to 600 million years ago.  The Paleozoic Era (from 600 million years to 250 million years ago).  The Mesozoic Era (from 250 million years to 70 million years ago).  The Cenozoic era (from 70 million years to the recent time). I. The Precambria Era (from 4.5 Billion to 600 Million years ago). What do you understand by the term Precambrian? The Precambrian Era is the oldest and longest geological era, covering about 5/6 of the earth’s geological time. The following geological events occurred in the Horn during this era. Þ Frequent orogenic movements (mountain building process by volcanic eruptions); Þ Intensive volcanic activities; Þ Denudation during the later periods (reduction or wearing down of the mountains); and Þ Formation of folded mountain. 17  Grade 9 | Geography NOTE During the Precambrian era: Þ The first forms of life (one-celled) emerged, such as amoeba, and jellyfish, and Þ The oldest rock formed – the old crystalline basement/ basement complex rock. This rock is found beneath all other rocks. Today, in a few areas of Ethiopia, outcrops of old crystalline basement complex rocks are found on the surface, due to continuous denudation. Example: Þ In central and northern Tigray; Þ In Mettekel, Assossa, Illubabor and the Abbay Gorge; Þ In central Sidama, southern Omo, southern Bale and Borena, and Þ In central, western and northern Eritrea. Figure 1.3: Geological Map of Ethiopia II. The Paleozoic Era (from 600 million years to 250 million years ago) Which life form was dominant in the Paleozoic era? During this era, in Ethiopia, the major geologic (geomorphic) process was denudation followed by peneplanation. No significant structural formation took place. Hence, the Paleozoic is the only era that left a gap in a rock formation in Ethiopia. The massive denudational activity resulted in the formation of inselbergs (residual features) in some parts of Ethiopia. 18  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA NOTE The Paleozoic era is known for the predominance of invertebrates. III. The Mesozoic Era (from 250 million years to 70 million years ago) Which life form was dominant in the Mesozoic era? This era was marked by alternate slow sinking and uplifting of the landmass (Epeirogenesis) of the Horn of Africa. The Mesozoic Era was an era of sedimentary rock formation in Ethiopia. The Mesozoic era has three distinct periods as indicated hereunder. Table 1.3 The Three Periods of Mesozoic Era Periods Geological time scale Triassic 250 - 180 millions Jurassic 180 - 135 millions Cretaceous 135 - 70 millions Triassic Period During this Period, the landmass sank due to internal forces. This event was followed by transgression of a nearby sea into the mainland of today’s Somalia and southeastern Ethiopia. During the Triassic Period, the oldest sedimentary rock known as Adigrat sandstone was formed. The Adigrat sandstone is the oldest in the southeast and progressively decreases in age to the northwest. Jurassic Period In this Period, the transgression of the sea continued into the mainland in the northwest direction. This event deposited another sedimentary rock known as Hintalo limestone. The Hintalo limestone in the northwest is younger while it is older in the southeast. 19  Grade 9 | Geography Cretaceous Period During this period, the landmass began to rise and the sea started to regress towards the southeast, depositing sedimentary rock known as Upper Sandstone. Upper Sandstone is the youngest sedimentary rock and therefore overlies the rest. Because of the direction of the regression and deposition, Upper Sandstone is the youngest in the southeast, and it is the oldest in the northwest. NOTE The transgression of the sea extended up to northwestern Ethiopia, as far as central Tigray and the western slopes of the western highlands. The sedimentary rocks formed in the Mesozoic Era were later buried by overlying Cenozoic igneous rocks. However, the sedimentary rocks have been exposed at the surface in some areas of Ethiopia. They are thinnest (because they are the youngest) in the southeast and thickest (because they are the oldest) in the northwest. One can see them exposed at the surface mostly in the southeastern lowlands of Ethiopia, central Tigray, and in the Abbay and Wabishebelle gorges. (For more information, look at the geological map of Ethiopia.) The Mesozoic is also known for the predominance of reptiles. Huge reptiles, such as dinosaurs, were dominant. However, at the end of this era, two other significant biological events occurred: Þ one was the disappearance of the dinosaurs, and Þ the other was the emergence of mammals, birds and flowering plants. IV. The Cenozoic Era (from 70 million years to the recent time) Do you know the era in which the Great East African rift valley was formed? It is the most recent geological era. During this era very significant structural, climatic and biological events have occurred in Ethiopia. Thus, geologic events of the Cenozoic era have greatly resulted in the development of very recent landforms in the Horn of Africa in general and Ethiopia in particular. The Cenozoic Era is divided into two periods namely, Tertiary and Quaternary. To make this lesson simple and comprehendible, we shall discuss only the geological 20  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA events of this era into events of each of the Periods. a. Geologic Events of the Tertiary Period - (70 million - 2 million years ago) In the Tertiary Period, the uplifting that began in the Cretaceous Period of the Mesozoic Era continued and reached its maximum height. In Ethiopia and the Horn it formed huge blocks of dome over the greater part of the region. As the uplifting continued through time, great cracks opened in the crust and resulted in the pouring out of extensive basaltic lava (known as the Trappean lava series). The lava resulted in the formation of: Þ the Northwestern Highlands, Þ the Southeastern Highlands, and Þ the Somali plateaus. As the cracking and faulting continued during the period, it formed the Great East African Rift Valley System – of which the Ethiopian Rift Valley System is part. The Great East African Rift system extends from Palestine-Jordan in the north to Malawi- Mozambique in the south, for a distance of about 7,200 kilometers. Of these, 5,600 kilometers is in Africa, and 1,700 kilometers in Eritrea and Ethiopia. b. Geologic Events of the Quaternary Period (2 million - recent years) This period is known for its recent volcanic activities that took place after the formation of the Rift Valley. In the Quaternary Period, the structures which were formed in Ethiopia and the Horn are: Þ the Afar Horst that extends into Djibouti, Þ the active volcano of Ertalle in Afar, Þ the dormant volcanic mountain of Fentalle in Eastern Oromia, Þ the extensive lava field and sheets of Metahara, Þ thermal springs and fumeroles of the rift valley, and Þ the Pluvial rainfall in Africa and the resultant deposition that took place in the lowlands of Ethiopia including the Rift Valley. 21  Grade 9 | Geography NOTE The Cenozoic Era in its Quaternary Period is assumed to be the period in which modern man evolved. Activity 1.3. Answer the following questions 1. What was the noticeable geological event of the Precambrian era in Ethiopia? 2. List the most important sedimentary rocks ever formed in Ethiopia during the Mesozoic era? 3. When was the Ethiopian rift valley formed? 4. By looking at a geological map of Ethiopia, identify the areas where these rocks are found on the surface as outcrops: a) Metamorphic rocks b) Sedimentary rocks c) Quaternary lava deposits 1.3.2 Landforms of Ethiopia Have you had opportunities to travel to the different regions of Ethiopia? If you have, what did you notice along your routes? Landform refers to individual earth surface features. As mentioned earlier sub- section, the landforms of Ethiopia are largely the result of the Cenozoic era’s tectonic and volcanic activities. Consequently, they are characterized by great diversity of highlands, plateaus, ambas, and rugged mountains, deep river gorges and lowlands. Altitude varies from about 116 meters below mean sea level at the Dallol depression (Kobar sink) to 4620 m above mean sea level (a.m.s.l.) at Ras Dashen in the Semein mountain system. Between these extreme points lie a number of mountains. If 1000 meters is chosen as a demarcating contour line between highlands and lowlands, 56 percent of Ethiopia’s land is highland. This fact has given Ethiopia the name “Roof of Eastern Africa.” It is the only country in the region with such a high proportion of elevated surface. This elevated surface is bisected diagonally by the Rift Valley 22  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA which extends from Syria to Mozambique across the East African lakes. Figure 1.4. Topography of Ethiopia These landforms are the results of two opposite forces: Þ the endogenic force that originates from inside the earth. For example, volcanic activity and tectonic forces, and Þ the exogenic force that originates at the surface (denudation and penepalantion). It is a combination of these two forces that created the existing landforms of Ethiopia. In terms of the geological and structural features that resulted from the two types of forces, the relief of Ethiopia can be divided into three main physiographic divisions (see Fig 1.4): I. The Western Highlands and Associated Lowlands II. The Southeastern Highlands and Associated Lowlands III. The Rift Valley 23  Grade 9 | Geography Figure 1.5. Ethiopian’ Main Topographic Regions I. The western Highlands and Associated Lowlands A. The Western Highlands Have you ever had a chance to go to Bahrdar, Gondar, Mekelle, etc.? The Western Highlands stretches from Tigray in the north to the highlands of Gamo and Goffa in southwest. They are separated from the southeastern highlands by the Rift Valley. It is the biggest physiographic region. It makes up 44% of the area of the country ( see Fig 1.5). The Western Highlands are the source of a large number of rivers and streams. Famous rivers like Abbay, Baro and Tekezze emerge from these highlands. As the rivers are cross boundary, they influence Ethiopia’s geopolitics role in north eastern Africa and the Middle East. Based on the internal altitudinal variability, the region is further sub-divided into four groups of highlands. a) The Plateau of Tigray b) The North Central Massif c) The Plateau of Shewa d) The Southwestern Highlands 24  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA a. The Plateau of Tigray Can you mention known mountain peaks in plateau of Tigray? The Tigrean plateau is the most northerly group of plateau bounded in the north by the Mereb River and in the south by the Tekezze river. It is drained by Mereb and the tributaries of the Tekezze. It is an area composed largely of sandstones and limestones, as the overlying basalt has been eroded. As a result, the soils are poor and thin. The plateau has been exposed to severe erosion due to long periods of human inhabitation. There are very high mountains on this plateau with elevations of over 3000 meters above sea level. Three of these are: Known mountain peaks on this sub-division include: Þ Mount Tsibet – 3988 m a.m.s.l. Þ Mount Ambalage – 3291 m a.m.s.l. Þ Mount Assimba – 3248 m a.m.s.l. b. The North Central Massif What makes the Northern central Massif distinct from the Massif of central Ethiopia? The north central Massif are found between the Abbay Gorge in the south and the Tekezze Gorge in the North. This massif contains the highlands of Gondar, Gojjam and Wollo. River Abbay and Tekezze along with their tributaries have formed a number of gorges and steep sided river valleys. The north central Massif are the most rugged and dissected plateaus of Ethiopia. They are capped by basalts of the tertiary period and surrounded by deep gorges. Within each of the plateaus are small arable lands known as ambas. The ambas are isolated from one another by gorges. The Mountain systems in Gondar and Gojjam are separated from the eastern group of mountains in Wollo by impenetrable and deep gorges. At one point though, they are connected by Yeju-Wadla Delanta land bridge (ridge). The western Massif make up the Massif of South Gondar (Semein), while the eastern ones make up the Lasta and Wollo Massif. South of these is found the Gojjam Massif. 25  Grade 9 | Geography The Gojjam Massif is the most extended tableland and is comparatively less dissected. It is formed on the core of the Amedamit-Choke mountains. It is carved by the Abbay river that effectively separated it from the Shewa plateau in the south and the Amhara Saynt Massif in the northeast. The North-Central Massif are known for the production of cereals, such as teff, pulses and oil seeds. Known mountain peaks in this Massif are: Þ Mount Ras Dashen – 4620 m a.m.s.l., Þ Mount Legeda – 4532 m a.m.s.l., Þ Mount Analu – 4480 m a.m.s.l., Þ Mount Tefaw Lezer – 4456 m a.m.s.l., Þ Mount Kolo – 4300 m a.m.s.l., Þ Mount Guna – 4231 m a.m.s.l., Þ Mount Abuna Yoseph – 4190 m a.m.s.l., and Þ Mount Hey – 4154 m a.m.s.l. C. The Plateau of Shewa (Central Plateau) Have you ever had the opportunity to travel from your locality to nearby plateau? If yes, what do you recognize all the way through until you reach any gorge? The Shewan Plateau is the smallest sub-division of the western highlands. It is a dome-shaped plateau that serves as a watershed between the Awash, Omo- Gibe and Abbay River basins. It extends westwards into western Wollega through Horo Guduru and forms a crescent shape which causes the Abbay to swerve and drain northwards. The Shewan plateau is separated from: Þ the plateau of Gojjam by the Abbay gorge in the north; Þ the southeastern highlands by the Awash River and the Rift Valley, and Þ the Highlands of Kafa by the Gibe River. The Plateau of Shewa is drained by the tributaries of the Abbay River in the west and the Awash River in the east. Its high mountains are found on its northeastern and south eastern margins; they are: Þ Mount Abbuye Meda – 4000 m a.m.s.l., and Þ Mount Guraghe – 3721 m a.m.s.l. 26  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA d. The Southwestern Highlands Which regional zones are found in the southwestern highlands of the Horn? The southwestern highlands lie south of the Abbay trough which is greatly eroded due to torrential rain that pours down in the area for almost all of the year. It is the wettest region of the country with a total average annual rainfall of above 1500 mm. They include the highland areas of Wollega, Illubabor, Jimma, Kafa and Gamo and Goffa. The region is drained: Þ Northwards, by the Dabus and Didesa tributaries of the Abbay River; Þ Westwards, by the headstreams of the Baro-Akobo River; Þ Southwards, by the Omo-Gibe River, which ends in Lake Turkana; and Þ Eastwards, by the right-bank tributaries of the Omo-Gibe (the Gojeb- Gibe River of Jimma Zone and Yem Special Woreda). The general elevation of these highlands is relatively low when compared to that of the Northern and Eastern Highlands. Only a few areas are above 2500 meters. The highest points in the region are the: Þ Gamo-Konso Highlands, Þ Maji-Korma Highlands, Þ Dawuro-Konta Highlands, Þ Tullu Wallel, and Þ Benishangul mountain. Mount Gughe has the highest altitude: 4200 m a.m.s.l. It is found in the Gamo plateau. These highlands are well-known for the production of coffee, inset, spice production, timbering, rubber tree production, cattle, honey, maize and high percentage of forest cover. Activity 1.4 Answer the following questions. 1. List the four sub-divisions of western highlands. 2. Why are northern mountains highly rugged? 27  Grade 9 | Geography B. The Western Lowlands The Western Lowlands extend from western Tigray in the north up to the southern Gamo and Goffa in the south, bordering the Sudan and South Sudan with a general elevation of 500-1000 m a.m.s.l. They are characterized by arid and semi-arid climate. The Baro-Akobo lowland is the wettest lowland compared to other lowlands of this physiographic division. That is why the rivers draining the region (particularly the Baro river) have almost a regular flow of water for much of the year. These lowlands of this physiographic region are sub-divided into: Þ the Tekezze and Angereb Lowlands, Þ the Abbay Dinder Lowlands, Þ the Baro-Akobo Lowlands, and Þ the Omo-Gibe Lowlands. The Tekezze and Angereb Lowlands are the most northerly lowlands, drained by Tekezze and Angereb. The Abbay Dinder Lowlands extend from south of Metema town up to the southern part of the Abbay River. Because of climatic hardship in most parts of these lowlands, the communities practice pastoralist and semi-pastoralist ways of life. However, there are notable towns, such as Humera, Kurmuk, Omedla and Metema that serve as business centers for the communities living along the Ethio-Sudanese border. II. The Southeastern Highlands and Associated Lowlands Can you propose what feature separates these highlands from the northwestern highlands? Which highlands are said to be the components of southeastern highlands of Ethiopia? This physiographic region is found to the southeast of the rift valley. This region is further divided into highland and lowland units. A. The Southeastern Highlands The Southeastern Highlands of Ethiopia include: a) the Hararghe plateaus, b) the Arsi plateau, c) the Bale Massif, and d) the Sidama highlands. 28  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA Their formation is similar to that of the North and Southwestern Highlands and they are capped by basaltic rock. They are the main sources of the Wabe Shebelle and Genale rivers. They are bounded: Þ in the west, by the fault line of the Rift Valley; Þ in the east, by the Ogaden Lowlands; and Þ in the south by the Elkerie and Borena Lowlands. a. The Hararghe Plateaus The Plateau of Hararghe rises sharply from the fault line of the Rift Valley and extends gently to the east up to Jigjiga. After Jigjiga, a fall in elevation takes place, giving way to the Ogaden Lowlands. The Plateau is drained by the left-bank tributaries of the Wabe Shebelle River. The basaltic rocks have been worn away, exposing limestones and earlier sedimentary rocks. The Hararge Plateau area and its foothills are significant producers of coffee, chat, sorghum and millet. The prominent mountain peaks include: Þ Mount Gara Muletta (3381 m a.m.s.l.), and Þ Mount Jebel Tita (3122 m a.m.s.l.). b. The Arsi Plateau This plateau area consists of the Gugu and Chillalo Massif. It is an extendingly rolling plateau; it is a very suitable plateau for farming. These features has been comparatively low because of the erosion on the Arsi plateau. The Arsi plateau is known for its wheat production. The highest points on the Arsi plateau are: Þ Mount Chillallo (4136 m a.m.s.l.), Þ Mount Bada (4139 m a.m.s.l.), and Þ Mount Kaka (4180 m a.m.s.l.). 29  Grade 9 | Geography c. The Bale Massif The Bale Massif is next to the Arsi Plateau but is separated from it by the headstreams of the Wabe Shebelle, popularly known as the Wabe River. In the north, the massif consists of a flat form that is similar to basaltic plateaus. The Bale massif is known for its barely. In its southern part, the massif consists of huge mountains. The highest points on the Bale Mountains are: Þ Mount Tulu Dimtu (4377 m a.m.s.l.), and Þ Mount Batu (4307 m a.m.s.l.). d. The Sidama Highlands The Sidama Highlands are separated from the Bale Highlands by the Genale river valley. The area constitutes the southwest extension of the southeastern highlands. The plateau slopes away gently to the south and southeast, and is drained by the Genale river and its tributaries. B. The Southeastern Lowlands These lowlands extend from the foot hills of the southeastern highlands along the Ethio-Somalian and Ethio-Kenyan borders. Their general elevations lie between 500 and 1000 m a.s.l. They consist of: Þ the Ogaden plains, Þ the Borena plains, and Þ the Elkeri plains, Þ the Genale plains. These landforms are highly extensive lowlands. They are characterized by extreme climatic condition with low annual rainfall-often below 500 mm. Most of these lowlands are covered by sandstones and recent marine deposits. The people practice a pastoralist way of life because of the harsh climate. 30  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA III. The Rift Valley What is the difference between a river valley system and a rift valley system? Can you give examples? The Ethiopian Rift Valley System is a narrow strip of land, which stretches from the Afar Depression in the north, through the Rift Valley Lakes’ region up to Lake Turkena and Chew Bhair. The Ethiopian Rift Valley System is part of the Great East African Rift Valley, which covers a distance of 5600 kms in Africa. The Great East African Rift System is a set of fractures in the earth’s crust that extend from the Jordan River valley in the north, through the Red Sea, and then across East and Central Africa to Mozambique in the south (Fig 1.6). Figure 1.6. The Rift Valley System of Ethiopia and the Horn The rift valley was, as indicated earlier, formed at the end of the Tertiary Period as a result of tectonic epeirogenic activity. The presence of active volcanoes, minor faulting, hot springs, cinder cones fumaroles and geysers could be good evidence for the unstable nature of the region geologically. As you can see in fig. 1.6, the Ethiopian Rift Valley System runs diagonally from northeast to southwest and divides Ethiopia Highlands into two. It covers a total length of 1700 kilometers in Ethiopia and Eritrea. 31  Grade 9 | Geography Covering a length of 1700 kms, the Ethiopian Rift Valley System comprises 18 percent of the country’s total area. It is subdivided into three main parts: a) The Afar Triangle (northern), b) The Main Ethiopian Rift or the Lakes’ Region (central), and c) The Chew-Bahir Rift (southern). a) The Afar Triangle (Northern Part) The Afar Triangle is the largest and widest part of the system extending 200-300 kilometers. Its altitude is generally low, ranging from 116 meters below mean sea level at the Kobar Sink to about 900 meters above sea level at Awash. Much of the area here lies below sea level. This part of the Ethiopian Rift System is characterized by Þ Faulted depressions (the Dallol Depression) and grabens (also called troughs), and Þ Cinder cones and Volcanic mountains Also, a large part of the area is covered by extensive salt plains and lakes (for instances, Lake Assale and Lake Afrera). The Afar triangle is bounded by parallel fault lines on the east and west. Its floor is made up of: Þ Grabens such as the Tendaho Graben, Þ Volcanic ash and lava deposits, Þ Lacustrian and fluvial deposits, and Þ Volcanic mountains such as Mount Fentalle. What is more, the Afar Triangle has special characteristics that do not exist in other regions of Ethiopia. It consists of: Þ Fossil rich sediments, and Þ Rich archeological sites have shown us that the area was the home of the ancient ancestors of primates and hominids. b) The Main Ethiopian Rift or the Lakes Region (Central Part) The central subdivision of the Ethiopian Rift system, i.e., the Main Ethiopian Rift, covers the area from the lower Awash basin up to Lake Chamo. This subdivision 32  UNIT ONE GEOLOGICAL HISTORY AND TOPOGRAPHY OF ETHIOPIA is the most elevated and narrowest part of the Ethiopian Rift Valley. It is also the wettest, most densely vegetated, and most densely populated. Unlike others, sedentary farming is practiced here. The area also includes numerous lakes of enormous economic and aesthetic value. c) The Chew-Bahir Rift (Southern Part) The southern subdivision of the Ethiopian Rift system, the Chew-Bahir Rift, is also known as the Omo-Gibe trough. It is the smallest section of the Ethiopian Rift System separated from the Lakes’ Region to the north by the Konso Highlands and its surroundings. It consists of an extensive shallow marshy area covered by tall grasses into which the Sagan and Woito streams end. In the vicinity of Arba Minch, this part of the Ethiopian Rift valley system is split into the Ganjuli and the Galena Valleys by the Amaro mountain range. At large, the Chew-Bahir Rift region is occupied by a pastoralist population. Activity 1.5. Answer the following questions 1. Draw a map of Ethiopia showing the major physiographic divisions. 2. Write down the peculiarities of the western and south eastern lowlands. 3. Why is the Baro-Akobo lowland the wettest of all lowlands? 4. Draw a map of the Rift Valley System in Ethiopia and demarcate its subdivisions. 33  Grade 9 | Geography UNIT SUMMARY Ethiopia is located in Eastern Africa within the 3oN-15oN latitudes and 33oE-48oE longitudes. Regarding shape, Ethiopia has more or less compact shape. In terms of size, Ethiopia is the tenth largest country in Africa. It has an area of 1,106,000 square kilometers. Because of its large size, Ethiopia enjoys a diverse climate, a great variety of fauna and flora, diversified ethnic groups and a large potential of arable land as well. The geological time scale measures time on a scale involving four major geological eras. The geological structure of Ethiopia is the result of the geological events that occurred during these eras. For example, crystalline basement complex rocks were formed during the Precambrian era; peneplanation took place during the Paleozoic era; land mass sinking and up-lifting were dominant during the Mesozoic era; formation of Ethiopian Rift Valley System during Cenozoic era respectively. The landforms of Ethiopia are largely the results of the Cenozoic era tectonic and volcanic activities. Consequently, Ethiopia has rugged mountains, plateaus, ambas, river gorges, a rift valley and lowlands. The altitudinal variation in Ethiopia ranges from the highest peak, Ras Dashen (4620 meters above sea level) to the lowest point, Kobar Sink (116 meters below mean sea level). UNIT ONE 34