Ethiopian Topography Textbook PDF

 CHAPTER THREE THE TOPOGRAPHY OF ETHIOPIA AND THE HORN By: Fentanesh Haile (Asst. Professor)  Introduction The topography of Ethiopia is largely determined by the geologic activities of the Cenozoic Era. The uplifting of the Arabo-Ethiopian swell and the...

 CHAPTER THREE THE TOPOGRAPHY OF ETHIOPIA AND THE HORN By: Fentanesh Haile (Asst. Professor)  Introduction The topography of Ethiopia is largely determined by the geologic activities of the Cenozoic Era. The uplifting of the Arabo-Ethiopian swell and the subsequent outpouring, spreading and thick accumulation of Trapean lava have given rise to an outward sloping highland plateau and mountains. Faulting elsewhere They also formed depressions on which lakes were subsequently created.  General Characteristics of the Ethiopian Physiography The Ethiopian landform is characterized by: Flat-topped plateaus, high and rugged mountains, deep river gorges and vast plains. -Altitude ranges from 125 meters below sea level (Kobar Sink) to the highest mountain in Ethiopia, Mount Ras Dashen (4,620 m.a.s.l), which is the fourth highest mountain in Africa. Ethiopia has the largest proportion of elevated landmass in the African continent.  Cont’d It is sometimes described as the Roof of East Africa because of its height and large area. More than 50% of the Ethiopian landmass is above 1,000 meters of elevation; and above 1,500 meters makes 44% of the country. Half of this, in turn, is at more than 2,000 meters above sea level. Most of the Ethiopian Highlands are part of central and northern Ethiopia, and its Northernmost portion extends into Eritrea. have been dissected by several rivers and ravines which have cut deep gorges.  Cont’d Most of the country consists of high plateau and mountain ranges that are sources of many rivers and streams that made the country to be described as the “Water Tower of East Africa”. The diversity in topography is accompanied by differences in other natural features such as soil, climate, vegetation and wild life. Likewise, the socio-cultural and economic phenomena are also affected by the topography.  Cont’d Taking the 1,000 meters contour line for the highland-lowland demarcation, one observes the following contrasting features between the Ethiopian highlands and lowlands; Characteristics of Ethiopian highlands:  Moderate and high amount of rainfall (>600 mm per year).  Lower mean annual temperature (2,000 m.a.s.l) constituting nearly 22%.  Characteristics of Ethiopian lowlands -In contrast to the highlands, the lowlands make up nearly the remaining 44% of the area of the Ethiopia. characterized by: Fewer amounts of rainfall and higher temperature. High prevalence of tropical diseases. (malaria, cholera, Chagas’ disease, yellow fever, and dengue) Lower population densities. Nomadic and semi-nomadic economic life. Vast plain lands favorable for irrigation agriculture along the lower river basins.  3.2. The Physiographic Divisions of Ethiopia three major physiographic units brought about by the geologic processes of the Cenozoic Era are: 1) The Western highlands and lowlands 2) The South-eastern (Eastern) highlands and lowlands 3) The Rift Valley 3.2.1. The Western Highlands and Lowlands  This physiographic unit includes all the area west of the Rift Valley.  It extends from north to south encompassing nearly the whole western half of Ethiopia.  It makes up about 44% of the area of the country.  In the east the western escarpment of the Rift Valley bound it whereas westward, the land gradually descends in altitude until it merges into the western foothills and lowlands, along the Sudan and South Sudan border.  This region is further subdivided into four groups of highlands (76.3%) and four groups of lowlands (23.7%) (See Fig. 3.1).  The Western Highlands a. The Tigray Plateau It extends from the Tekeze gorge in the south to central Eritrean highlands. The Tigray plateau is separated from the Eritrean plateau by the Mereb River. It lies to the southeast of the upper course of the Mereb/Gash River and to the northeast of Tekeze River Gorge. It constitutes about 13% of the area of the region. It is an elongated highland with most of the land being in between 1,000 and 2,000 meters above sea level. The right bank tributaries of Tekeze drain this plateau. There are high mountains in this plateau with elevations of over 3000 meters, namely Mount Tsibet (3988 m.a.s.l), Mount Ambalage (3291 m.a.s.l), and Mount Assimba (3248 m.a.s.l).  b. North Central Massifs This Physiographic division is the largest in the western highlands Much of its northern and southern limit follows the Abay and Tekeze gorges. The Abay, Tekeze and their tributaries have cut into this region a maze of gorges, steep sided river valleys, dividing the land into many isolated plateau blocks, precipitous tablelands and other rugged surface forms. In its central part, the physiographic unit also accommodates the Lake Tana basin surrounded by plains of Fogera and Dembia in the north and an upland plain in its south.  Cont’d 58% of the region is at an altitude of more than 2,000 meters, making it, next to the Shewan Plateau, the second highest physiographic division. (Shewan Plateau has largest proportion of elevated ground in WPR) The region consists of the Gonder, Wello and Gojjam Massifs. Out of the 26 mountain peaks with altitude of more than 4,000m.a.s.l in Ethiopia, 19 mountain peaks are found in this physiographic region Among these, the most popular ones include Mount Ras Dashen (4,620 m.a.s.l), Mount Weynobar/Ancua (4462 m.a.s.l), Mount KidisYared (4453 m.a.s.l), and Mount Bwahit (4437 m.a.s.l) in the Simen Mountain System.  Cont’d Mount Guna (4,231m.a.s.l) in the Debre Tabour Mountain System, Abune Yoseph (4,260 m.a.s.l) in the Lasta highlands of Wello and Mount Birhan (4,154 m.a.s.l) in the Choke Mountain System in Gojjam are also part of Simen Mountain System. These mountains have steep cliffs and rugged terrain that provide scenic views to climbers. The Mountain systems in Gonder and Gojjam are separated from the eastern group of mountains in Wello by impenetrable and deep gorges. At one point though, they are connected by Yeju- Wadla Delanta land bridge (ridge).  c. The Shewa Plateau/central highlands is bounded by the Rift Valley in the east and southeast, by the Abay gorge in its northern and western limit, and the Omo gorge in the south and west. the Shewa Plateau is the smallest of the Western highlands with only 11% of the area of the whole physiographic region Nearly ¾ of its area is at an altitude of more than 2,000 meters above sea level.  Cont’d The Shewa plateau is drained, outward in all directions by the tributaries of Abay, Omo, and Awash. It, therefore, forms a water divide for these three river basins. The tributaries of Abay:- Guder, Muger, Jema etc. have cut deep gorges and steep sided river valleys. the tributaries of Omo and Awash have dissected the other sides of the plateau. this plateau has relatively extensive flat-topped uplands, giving it the appearance of a true plateau. The highest mountain in the Shewan plateau is Mount Abuye-Meda (4,000 m.a.s.l) in Northern Shewa, Mount Guraghe in the south is 3,721 meters high.  d. The Southwestern Highlands Consists of the highlands of Wellega, Illuababora, Jimma, Kaffa, Gamo and Gofa. This region is separated from the adjacent highlands by the Abay and Omo river valleys. It extends from the Abay gorge in the north to the Kenya border and Chew Bahir in the south. It accounts for 22.7% of the area of the region. The region is the second largest in the Western highlands. About 70% of its area lies within 1,000-2,000 meters altitude The southwestern plateau is the wettest in Ethiopia  Cont’d It is drained by Dabus, Deddessa (tributaries of Abay), Baro, Akobo and the Ghibe/Omo rivers. The numerous streams have cut these highlands to produce the most dissected and rugged terrain that accommodates the most numerous and diverse ethnic linguistic groups in Ethiopia. With a height of 4,200 m a s l, Guge Mountain is the highest peak in this physiographic subdivision  The Western Lowlands These are the western foothills and border plains that extend from Western Tigray in the north to southern Gamo-Gofa in the South. In certain places, ridges or part of the highlands protrude into the lowlands, interrupting their continuity. They make 11% of the area of the physiographic region. The general elevation ranges between 500 and 1000 meters above sea level.  Tekeze lowland,  Abay-Dinder lowland,  Baro lowland, and  Ghibe lowland With the exception of the Baro lowland, the region is generally characterized by arid or semi-arid conditions. Pastoral or semi-pastoral economic activities dominate the area. As one moves northwards, the degree of aridity increases, making rain-fed agriculture more difficult.  Cont’d Since one or two rivers cross all of these lowlands, irrigation agriculture is highly feasible. For example, the Baro lowland has an extensive flat area suitable for mechanized agriculture. The Ghibe/Omo lowland, includes the lower Ghibe/Omo Valley and the northern section of the Turkana basin is classified in the Western lowlands from its geographical location. But structurally it also belongs to the Rift Valley. It is an area, which is both faulted and tectonically depressed. The Western Lowlands importance could be related to agriculture, history, or are simply border towns and frontier ports. These are Humera(W.Tig), Metema (NW. Amh), Omedla, Kurmuk(SW. Begu), Gambella (N. Gamb) etc. 3.2.2. The Southeastern Highlands and Lowlands It accounts for 37% of the area of Ethiopia. The highlands make up 46% of the physiographic division while the rest is lowland. bordered by eastern escarpment of the Rift Valley in the west and north, In many places the land raises so abruptly that from the edge of the plateau one literally looks down the Rift Valley. From here, the land gradually descends southeastward into the southeastern lowlands and then to the plains of Somalia.  Cont’d Further subdivided into two units of highlands and two units of extensive lowlands  The Southeastern Highlands A. The Arsi-Bale-Sidama Highlands  These highlands are found to the east of the Lakes Region.  They are located in the south western section of the physiographic region.  They make up 28.5% of the area of the region and 62% of the south - Eastern Highlands.  Cont’d i) The Arsi Highlands are made up of flat rolling uplands and dissected mountains. The well-known mountains in this area are Mount Kaka (4,180 m.a.s.l), Mount Bada (4,139 m.a.s.l) and Mount Chilalo (4,036 m.a.s.l). ii)The Bale highlands are separated from the Arsi highlands by the head and main stream of Wabishebelle. They consist of a platform looking basaltic plateau in the north-central part and high mountain massif to the south. The Afro-Alpine summit of Senetti plateau is found on this group. The highest mountain peaks in this region are Tulu-Demtu (4,377 m.a.s.l) and Mount Batu (4,307 m.a.s.l). Erosion features belonging to Pleistocene glaciation but later modified by fluvial processes are seen in the trough-like gorges, hanging valleys, and depressions.  Cont’d N:B Weyb River, tributary of Ghenale, has cut an underground passage (Sof Omar cave) through the Mesozoic Limestone rocks. The cave is found near Bale Mountains. It is one of the World's most spectacular and extensive underground caverns creating a magnificent view accessible only by an underground stream. iii)The Sidama Highlands are separated from the Bale Highlands by the Ghenale river valley. They occupy the southwestern corner of this region. The prominent feature here is the Jemjem plateau, an important coffee growing area. Rivers Wabishebelle and Ghenale along with their tributaries have dissected this physiographic region.  B. The Hararghe Plateau This plateau is a north-easterly extension of the south-eastern highlands. extends from the Chercher highlands in the south-west to Jigjiga in the east. It makes up 38% of the South Eastern highlands and 17.4% of the whole physiographic region. It has the smallest proportion of upper highland (>2,000 meters). It is a low lying and elongated region. The left-bank tributaries of Wabishebelle drain it. Much of the Trappean lava is removed and the Mesozoic rocks are extensively exposed. Babile1.bmp, Babile 2.bmp, Babile3.bmp, Babile 4.bmp The highest mountain here is Mount Gara-Muleta (3,381 m.a.s.l).  The Southeastern Lowlands located in the southeastern part of the country and the most extensive lowlands. They make up 54% of the area of the physiographic region and around one-fifth of the country. divided into Wabishebelle plain (60%) and the Ghenale Plain (40%). include the plain of Ogaden, east of Wabishebelle Elkere plain b/n Ghenale and Wabishebelle and Borena west of Ghenale basin These extensive plains are interrupted here and there, by low hills, low ridges, inselbergs and by shallow and broad river valleys and depressions.  Cont’d these lowlands are little used and support very small population/ sparsely populated due to the harsh climatic conditions. inhabited by pastoral and semi-pastoral communities, The economic potential for this region includes animal husbandry, irrigation, agriculture and perhaps exploitation of petroleum and natural gas.  3.2.3. The Rift Valley is a tectonically formed structural depression It is bounded by two major and more or less parallel escarpments. It covers 18% of the area of Ethiopia. It is elongated and funnel shaped, with a NE-SW orientation. It opens out in the Afar Triangle, where it is the widest, and narrows down to the south. The floor of the Rift Valley is made up of interconnected troughs, grabens and depressions. Volcanic rocks, fluvial and lacustrine deposits cover the floor. In many places, numerous volcanic domes, hills and cinder cones rise from the floor.  Cont’d Altitude in the floor ranges from 125 meters below sea level at Dallol Depression, to as high as 2,000 meters above sea level in the Lakes region. The bounding escarpments are also of varying heights. From the floor to the edge of the escarpment, the heights vary from 200 to 1500 meters. the climate also varies from warm, hot and dry to cool and moderately moist conditions resulted in variation of social and economic life There are places, which are desolate/ uninhabited, and sparsely inhabited by pastoralists where as in other parts people  Cont’d The Rift Valley is subdivided into three physiographic sub-regions.  the Afar Triangle,  the Main Ethiopian Rift, and  the Chew Bahir Rift. i. The Afar Triangle  is the largest and widest part of the Rift Valley  makes up 54% of the Rift Valley area.  It is bounded by the high western and eastern escarpments in the west and east respectively, and by the Afar and Aisha Horst in the northeast.  Cont’d morphology of the Afar depression, triangular-shape lowland, where elevation drops uniformly from approximately 1,000 meters in the southwest to below sea level in the north (Danakil depression) and in the east, where the shores of Lake Asal, fluctuating at around 125 meters below sea level, represent the lowest subaerial point of the African continent. The area is generally of low altitude (300-700 meters). The depression, hosts one of the most hostile environments on Earth (maximum temperatures can exceed 50°C during the summer wet season; -Dallol, at the northern tip of Afar.  Cont’d characterized by faulted depressions (grabens), volcanic hills, active volcanoes, volcanic ridges, lava fields and low lava platforms. Lakes (Abe, Asale, and Afrera) occupy some of these basins. A prominent feature in this region is the Denakil Depression (Kobar Sink) Separated from the Red Sea by a 200 meters high land barrier, much of it lies below sea level.  A larger part of this is covered by thick and extensive salt plain. Lake Asale and Lake Afrera occupy the lowest parts of this sunken depression. The Afar Triangle is generally hot and dry The economic importance: salt extraction, irrigation along the Awash River and electric potential from geothermal energy ii. The Main Ethiopian Rift/Central Rift It refers to the narrow belt of the Rift Valley that extends from Awash River in the north to Lake Chamo in the south. bounded by the western and eastern escarpments. With the exception of the Arbaminch area, the bounding escarpments are generally low. is the narrowest and the highest It has an average width of 50-80 kilometers and general elevation of 1,000-2,000 meters above sea level. The floor in many places is dotted by cinder cones and volcanic mountains. The big ones include Mount Fentale, Boseti-guda (near Adama), Aletu (north of Lake Ziway) and Chebi (north of Lake Hawasa).  Cont’d Because of altitude, the lakes region of the Main Ethiopian Rift is generally milder and watery. Here rain-fed agriculture is practiced. Other resource bases include the recreational value of the lakes, the agricultural importance of some streams and lakes, and the geothermal energy potential.  iii. The Chew Bahir Rift This is the smallest and the southern-most part of the Rift Valley Gneissic highlands of Konso and the surrounding highlands separate it from the Main Ethiopian Rift to the north. characteristic feature of this region is the broad and shallow depression, which is a marshy area covered by tall grass, into which the Segen and Woito streams empty.  3.3. The Impacts of Relief on Biophysical and Socioeconomic Conditions 1. Agricultural practices Relief influences farm size and shape in that in an area of rugged terrain the farmlands are small in size and fragmented and tend to be irregular in shape. Choice of farming techniques and farm implements are highly influenced (in rugged terrain mechanized farming techniques are difficult to practice). influences crop production as some corps are well adapted to higher altitudes (barley, wheat) and others to low altitude (sorghum, maize). influences the practice of animal husbandry as most equines and sheep are reared in the higher altitudes and camels and goat are well adapted to lower altitudes  2. Settlement pattern Highlands of Ethiopia that experience a temperate type of climatic condition that are mainly free from most of the tropical diseases are densely settled. Rugged and difficult terrain hinders the development of settlement and its expansion.  The highlands of Ethiopia are characterized by sedentary life and permanent settlements while lowlands that are inhabited by pastoralists have temporary settlements.  3. Transportation and communication  The highly dissected nature of the landscape is a barrier to the development of internal surface transportation that resulted in the long-term isolation of many communities The difficult terrain makes infrastructure development and maintenance costly. TV and radio communications are also highly influenced by relief. The rugged topography rendered rivers less navigable due to the waterfalls, deep gorges and steep cliffs.  4. Hydroelectric power potential The great difference in altitude coupled with high rainfall created suitable conditions for a very high potential for the production of hydroelectric power in Ethiopia. 5. Socio-cultural feeling The rugged terrain as a result of excessive surface dissection resulted in the long-term isolation of communities that led to the occurrence of cultural diversity. People who live in the highlands have been identifying themselves as degegnas (mountaineers) and those who live in the lowlands as kollegnas (lowlanders).  6. Impacts on climate The climate of Ethiopia is a result of the tropical position of the country and the great altitudinal variation of the general topography. Highlands with higher amount of rainfall and lower rate of evapo-transpiration tend to be moisture surplus compared to the moisture deficit lowlands. 7. Impacts on soil - Steep mountain slopes have shallow and little developed soils. 8. Impacts on natural vegetation - Relief through its effect on climate and hydrology affect the type of natural vegetation grown in an area. Q???