Ethiopian Highlands

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Ethiopian Highlands with Ras Dashan in the background.

The Ethiopian Highlands are a rugged mass of mountains in Ethiopia, Eritrea (which is sometimes referred to as the Eritrean Highlands), and northern Somalia (Somaliland) in northeastern Africa. The Ethiopian Highlands form the largest continuous area of its altitude in the whole continent, with little of its surface falling below 1500 m (5000 ft), while the summits reach heights of 4600 m to 4900 m (15,000 to 16,000 ft). It is sometimes called the Roof of Africa for its height and large area it covers.^[1]

1 Geography
2 Geology
3 Ecology
4 See also
5 References
6 External links

[edit] Geography

The Highlands are divided into northwestern and southeastern portions by the Great Rift Valley, which contains a number of salt lakes. The northwestern portion, which covers the Tigray and Amhara Regions, includes the Semien Mountains, part of which has been designated a national park. Its highest peak, Ras Dashan (4533 m), is the highest peak in Ethiopia and the fourth-highest in Africa. Lake Tana, the source of the Blue Nile, also lies in the northwestern portion.

The southeastern portion's highest peaks are located in the Bale Zone of Ethiopia's Oromia Region. The Bale Mountains, also designated a national park, are nearly as high those of Semien, with peaks over 4000 m, such as Tullu Demtu (4337 m and the second-highest peak in Ethiopia) and Batu (4307 m).

[edit] Geology

Dendi Caldera, a collapsed volcano in the mountain region

The Ethiopian Highlands began to rise 75 million years ago, as magma from the earth's mantle uplifted a broad dome of the ancient rocks of the African Craton. The opening of the Great Rift Valley split the dome of the Ethiopian Highlands into three parts; the mountains of the southern Arabian Peninsula are geologically part of the ancient Ethiopian Highlands, separated by the rifting which created the Red Sea and Gulf of Aden and separated Africa from Arabia.

Around 30 million years ago, a flood basalt plateau began to form, piling layers upon layers of voluminous fissure-fed basaltic lava flows. Most of the flows were tholeiitic balts, save for a thin layer of alkali basalts and minor amounts of felsic (high-silica) volcanic rocks, such as rhyolite. In the waning stages of the flood basalt episode, large explosive caldera-forming eruptions also occurred.

The Ethiopian Highlands eventually became bisected by the Great Rift Valley, as the African continental crust pulled apart. This rifting gave rise to large alkaline basalt shield volcanoes beginning about 30-31 million years ago.^[2]

[edit] Ecology

Because the highlands elevate Ethiopia, located close to the equator, this has resulted in giving this country an unexpectedly temperate climate. Further, these mountains catch the precipitation of the monsoon winds of the Indian Ocean, resulting in a rainy season that lasts from June until mid-September.^[3] These heavy rains cause the Nile to flood in the summer, a phenomenon that puzzled the ancient Greeks.

The Ethiopian Highlands share a similar flora and fauna of other mountainous regions of Africa; this distinctive flora and fauna is known as Afromontane. The Highlands are home to a number of endemic species, such as the Walia Ibex and Ethiopian Wolf.

At lower elevations, the highlands are surrounded by tropical savannas and grasslands, including the Sahelian Acacia savanna to the northwest, the East Sudanian savanna to the west, and the Somali Acacia-Commiphora bushlands and thickets to the northeast, east, south, and through the Rift Valley.

The highlands themselves are divided into three distinct ecoregions, distinguished by elevation. The Ethiopian montane forests lie between 1,100 and 1,800 meters elevation, above the lowland grasslands and savannas. This woodland belt has several plant communities. Kolla, is an open woodland found at lower elevations, and dominated by species of Terminalia, Commiphora, Boswellia, and Acacia. Weyna dega is a woodland found in moister and higher locations, dominated by the conifers Afrocarpus gracilior and Juniperus procera. The lower portion of the Harenna forest is a distinct woodland community, with an open canopy of Warburgia ugandensis, Croton macrostachyus, and Syzygium guineense, and Afrocarpus gracilior, with wild coffee (Coffea arabica) as the dominant understory shrub.

The Ethiopian montane grasslands and woodlands occupies the area between 1800 and 3000 meters elevation. The natural vegetation was closed-canopy forest in moister areas, and grassland, bushland, and thicket in drier areas. A few areas of natural vegetation remain. Drier areas covered with forests of the forest consists of Podocarpus falcatus and Juniperus procera, often with Hagenia abyssinica. In the Harenna forest, pockets of moist, closed-canopy forest with Aningeria and Olea are draped with lianas and epiphytes, while above 2400 meters, a shrubby zone is home to Hagenia, Schefflera, and giant lobelias. The evergreen broadleaved forest of the Semien Mountains, between 2,300 and 2,700 meters elevation, is dominated by Syzygium guineense, Juniperus procera, and Olea africana.

Above 3000 meters elevation lie the Ethiopian montane moorlands, the largest afroalpine region in Africa. The montane moorlands lie above tree line, and consists of grassland and moorland with abundant herbs and some shrubs. The Ethiopian Wolf is endemic to the montane moorlands, and is critically endangered.