Topography and Drainage

Topography and Drainage

Much of the Ethiopian landmass is part of the East African Rift Plateau. Ethiopia has a general elevation ranging from 1,500 to 3,000 meters above sea level. Interspersed on the landscape are higher mountain ranges and cratered cones, the highest of which, at 4,620 meters, is Ras Dashen Terara northeast of Gonder. The northernmost part of the plateau is Ethiopia's historical core and is the location of the ancient kingdom of Aksum. The national capital of Addis Ababa ("New Flower") is located in the center of the country on the edge of the central plateau.

Millennia of erosion have produced steep valleys, in places 1,600 meters deep and several kilometers wide. In these valleys flow rapid streams unsuitable for navigation but possessing potential as sources of hydroelectric power and water for irrigation.

The highlands that comprise much of the country are often referred to as the Ethiopian Plateau and are usually thought of as divided into northern and southern parts. In a strict geographical sense, however, they are bisected by the Great Rift Valley into the northwestern highlands and the southeastern highlands, each with associated lowlands. The northwestern highlands are considerably more extensive and rugged and are divided into northern and southern sections by the valley of the Abay (Blue Nile).

North of Addis Ababa, the surface of the plateau is interspersed with towering mountains and deep chasms that create a variety of physiography, climate, and indigenous vegetation. The plateau also contains mountain ranges such as the Chercher and Aranna. Given the rugged nature of these mountains and the surrounding tableland, foreigners receive a false impression of the country's topography when Ethiopians refer to the landform as a plateau. Few of these peaks' surfaces are flat except for a scattering of level-topped mountains known to Ethiopians as ambas.

Southwest of Addis Ababa, the plateau also is rugged, but its elevation is slightly lower than in its northern section. To the southeast of Addis Ababa, beyond the Ahmar and Mendebo mountain ranges and the higher elevations of the southeastern highlands, the plateau slopes gently toward the southeast. The land here is rocky desert and, consequently, is sparsely populated.

The Great Rift Valley forms a third physiographic region. This extensive fault system extends from the Jordan Valley in the Middle East to the Zambezi River's Shire tributary in Mozambique. The segment running through central Ethiopia is marked in the north by the Denakil Depression and the coastal lowlands, or Afar Plain, as they are sometimes known. To the south, at approximately 9° north latitude, the Great Rift Valley becomes a deep trench slicing through the plateau from north to south, its width averaging fifty kilometers. The southern half of the Ethiopian segment of the valley is dotted by a chain of relatively large lakes. Some hold fresh water, fed by small streams from the east; others contain salts and minerals.

In the north, the Great Rift Valley broadens into a funnel-shaped saline plain. The Denakil Depression, a large, triangle-shaped basin that in places is 115 meters below sea level, is one of the hottest places on earth. On the northeastern edge of the depression, maritime hills border a hot, arid, and treeless strip of coastal land sixteen to eighty kilometers wide. These coastal hills drain inland into saline lakes, from which commercial salt is extracted. Along the Red Sea coast are the Dahlak Islands, which are sparsely inhabited.

In contrast with the plateau's steep scarps along the Great Rift Valley and in the north, the western and southwestern slopes descend somewhat less abruptly and are broken more often by river exits. Between the plateau and the Sudanese border in the west lies a narrow strip of sparsely populated tropical lowland that belongs politically to Ethiopia but whose inhabitants are related to the people of Sudan. These tropical lowlands on the periphery of the plateau, particularly in the far north and along the western frontier, contrast markedly with the upland terrain.

The existence of small volcanoes, hot springs, and many deep gorges indicates that large segments of the landmass are still geologically unstable. Numerous volcanoes occur in the Denakil area, and hot springs and steaming fissures are found in other northern areas of the Great Rift Valley. A line of seismic faults extends along the length of Eritrea and the Denakil Depression, and small earthquakes have been recorded in the area in recent times.

All of Ethiopia's rivers originate in the highlands and flow outward in many directions through deep gorges. Most notable of these is the Blue Nile, the country's largest river. It and its tributaries account for two-thirds of the Nile River flow below Khartoum in Sudan. Because of the general westward slope of the highlands, many large rivers are tributaries of the Nile system, which drains an extensive area of the central portion of the plateau. The Blue Nile, the Tekezé, and the Baro are among them and account for about half of the country's water outflow. In the northern half of the Great Rift Valley flows the Awash River, on which the government has built several dams to generate power and irrigate major commercial plantations. The Awash flows east and disappears in the saline lakes near the boundary with Djibouti. The southeast is drained by the Genale and Shebele rivers and their tributaries, and the southwest is drained by the Omo.


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