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Ethiopia and its Relief

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The specific features of the various relief and drainage area are considered later in the atlas. This map is concerned with the general characteristics of the relief of the country.

The major physical features are the results of the extensive and spectacular faulting which cracked the old crystalline block of the African continent along its eastern side producing features which stretch from Africa’s juncture with the eastern end of the Mediterranean Basin to Mozambique in the South.

The uplifting which resulted produced the high plateau – lands which are characteristic of the central regions of Ethiopia and which stand at a general elevation of between 2000 and 2500 metres above sea level.

However, the cracking also produced the clearly defined rift valley structures formed between parallel fault lines as the main blocks continued their upward movement. The floor of the Rift Valley, which stretches from the Red Sea through, (and includes the adjacent Afar Plains), south and over the border into Kenya.

It separates the main plateau area which occupies the western half of Ethiopia from the plateaulands of the south west, and, in the central regions of the country, stands at around 1000 metres below the general level of the plateaus.

Major features of the Ethiopian landscape the therefore the lines of the great escarpments overlooking the Afar plains.

These converge in the latitude of Addis Ababa to produce the Rift Valley lakes region which is a major area of inland drainage. In addition, fault structures have produced escarpments along the western borderlands of Ethiopia.

Three smaller features, the through of the lower Omo river, the highlands of the Afar horst bordering the Red Sea, and the area of the Kobar sink (Afar Depression) which is around 110 metres below sea level, are also the result of faulting.

The earth movements which affected the continental block in the eastern African region were associated with widespread volcanic activity which produced thick deposits of hard plateau basalts.

These are responsible for the flat surfaces which are characteristic of many areas in the highlands. The Bale Mountain area, for example, is the largest area of land above 10,000 metres on the continent of Africa.

However, continuing volcanic activity resulted in the building up of higher mountain areas which now dominate the plateau surface several regions, the most notable being the Simen Mountain Massif which rises to 4620 metres above sea level in Ras Dejen.

Other examples are Abuye Meda (4000 metres) which dominates the eastern escarpment area, Mt. Chilalo (4139 metres) in Arsi, Mt. Batu (4307 metres) in the Bale mountain region, Tulu Welel (3302 metres) in Western Welega Region, and Mt. Guge (4200 metres) in north eastern Gamo Gofa Region. Volcanic mountain structures are also found on the fringes and on the floor of the Rift Valley system. Examples are Mt. Wechecha (3385 metres), Mt. Ziquala (2989 metres) and Mt. Chubbe (2592 metres) in the Lakes Rift region.

The Pluvial Periods in Africa, (comparable with the Ice Ages of more northern latitudes), were responsible for the further shaping of the Ethiopian landscape, and produced the deep gorges which have dissected the high plateau lands.

The central regions of Ethiopia are most characteristic of this plateau and gorge landscape where river beds are often 2000 metres below the general level of the plateau surface, and where the hard surface basalts have resulted in abrupt edges to the gorges, overlooking a series of lower terraces which mark the underlying layers of softer sedimentaries.

The most well-known and the largest of these features is the gorge of the Abay (Blue Nile) river.

In general, the inclinations produced by uplift have resulted in the development of river systems which drain the highlands towards the north-west and the south-east, with closed river basins associated with the Rift Valley system between these two.

Ethiopia’s relief thus contributes to drainage towards both the Mediterranean Sea and Indian Ocean.

Limited area in Ethiopia lie below the 500 metre contour line. These are to be found adjacent to the Red Sea (including the area which has sunk below sea level); in the eastern and south-eastern extremities of the Ogaden area and Bale region, including the middle section of the Wabe Shebele valley and in the Gambela panhandle in western Ethiopia where the courses of the Baro and Akobo rivers enclose a section of the Sudan plains.

The Ethiopian relief includes therefore a range of altitudes stretching from below sea level to nearly 4600 metres above sea level, although, within these latitudes, this is not sufficiently high to bring the landscape within a permanent snow line as is the case in eastern Africa to the south. Within these extremes, about 50% of the land surface is above the 1500 metre contour line.

Traditional descriptions of the landscape (which are also associated with the broader classification into ecological zones) define:

(a) Woorch (the coldest highlands above 3500 metres)
(b) Dega (the cool highlands above 2500 metres)
(c) Woyna-Dega (warm lands between 1500 and 2500 metres)
(d) Kolla (the hot and relatively low lying lands below 1500 metres)
(e) Haroor (the hottest lowlands below 500 metres)

(Source: National Atlas of Ethiopia)

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