The Afar Depression (also called the Danakil Depression) is a geological depression in the Horn of Africa, where it overlaps Eritrea, the Afar Region of Ethiopia, and Djibouti. Afar is familiar as one of the cradles of hominids: Lucy, the fossilized specimen of Australopithecus afarensis, was found here. The Afar Depression includes the lowest point in Africa, Lake Asal (−155 meters {−500 ft}). The climate varies from warm 25 °C (77 °F) during the rainy season (September-March) to extremely hot 48 °C (118°F) during the dry season (March-September). Only the Awash River flows into the depression, where it ends in a chain of lakes that increase in salinity.
Environment
The lowlands of the Afar Depression are dominated by heat and drought. There is no rain for the most of the year; yearly rainfall averages range from 100 to 200 millimeters (4 to 7 in), with less rain falling closer to the coast. The Awash River, flowing north-eastward through southern Afar, provides a narrow green belt and enables life for the Afars, the nomadic people living in the Danakil desert, and for all other flora and fauna in the area. About 128 kilometers (79 miles) from the Red Sea, the Awash ends in a chain of salt lakes, where its water evaporates as fast as it is supplied. About 1200 kilometers² (463 miles²) of the Afar Depression is covered by salt, and salt mining is still a major source of income for many Afar tribes.
The Afar Depression biome is characterized as desert scrubland. Vegetation is mostly confined to drought-resistant plants such as small trees (e.g. species of the dragon tree), shrubs, and grasses. Wildlife includes many ungulates including Grevy's Zebra, Soemmering’s Gazelle, Oryx Beisa and, notably, the last viable population of African wild ass (Equus africanus somalicus). Birds include the ostrich, the endemic Archer's lark (Heteromirafra archeri), the Secretary Bird, Arabian and Kori bustards, Abyssinian Roller and Crested Francolin. In the southern part of the plain, in Ethiopia, lies the Mille-Sardo Wildlife Reserve (established 1973). Many fossils have been found in the Awash region, not only hominids but also elephantoids, crocodiles and hippopotamus.
Geology
The Afar Depression is a plate tectonic triple junction where the spreading ridges that are forming the Red Sea and the Gulf of Aden emerge on land and meet the East African Rift. The Afar Depression is one of two places on Earth where a mid-ocean ridge can be studied on land, the other being Iceland. The Afar is slowly pulling apart, at a rate of 1–2 centimeters (0.3–0.8 in) per year.
The floor of the Afar Depression is composed of lava, mostly basalt. One of Earth's great active volcanoes, Erta Ale, is found here. The Afar Depression and Triple Junction also mark the ___location of a mantle plume, a great uprising of mantle that melts to yield basalt as it approaches the surface (other mantle plumes can be found beneath the great volcanic islands of Iceland, Hawaii and Galapagos; also a mantle plume is responsible for Yellowstone in the USA).
References
- Alebachew Beyene and Mohamed G. Abdelsalam, 2005. "Tectonics of the Afar Depression: A review and synthesis." Journal of African Earth Sciences, Volume 41, Issues 1-2, pp 41-59
- Kloos, Helmut (1982) 'Development, drought and famine in the Awash valley of Ethiopia', African Studies Review, vol. 25, no. 4, p. 21-48.
- [World Wildlife Fund] (2001) 'Ethiopian xeric grasslands and shrublands (AT1305)' online version.