Afar Triangle

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MODIS satellite image of the Afar Depression and surrounding regions of the Red Sea, Gulf of Aden, Arabia, and the Horn of Africa.


The Afar Depression (also called the Danakil Depression or the Afar Triangle) is a geological depression in the Horn of Africa, where it overlaps Eritrea, the Afar Region of Ethiopia, and Djibouti. Afar is well known as one of the cradles of hominids, containing the Middle Awash, site of many fossil hominid discoveries; Gona, site of the world's oldest stone tools; and Hadar, site of Lucy, the fossilized specimen of Australopithecus afarensis.

The Afar Depression includes the lowest point in Africa, Lake Asal (–155 meters or –500 ft). It is one of the hottest places year-round anywhere on Earth. The climate varies from around 25 °C (77 °F) during the rainy season (September–March) to 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 most of the year, and yearly rainfall averages range from 100 to 200 millimetres (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 flora and fauna in the area and for the Afars, the nomadic people living in the Danakil desert. About 128 kilometres (79 miles) from the Red Sea, the Awash ends in a chain of salt lakes, where its water evaporates as quickly as it is supplied. About 1200 km² (463 sq mi) of the Afar Depression is covered by salt, and salt mining is still a major source of income for many Afar tribes.

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Perspective view of the Afar depression and environs, generated by draping a Landsat image over a Digital elevation model. Image generated by Allison Thurmond.


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 herbivores such as 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.

According to proponents of the aquatic ape hypothesis, the depression formed a small sea roughly 8 million years ago. The theory proposes to explain certain human characteristics (e.g. hairlessness, bipedality) in terms of adaptation to this semi-aquatic environment.[1]

Geology

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Simplified geologic map of the Afar Depression, after A.Beyene and M.G.Abdelsalam (2005).
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Location of the depression and local fault lines
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 central meeting place for these three pieces of Earth's crust is around Lake Abbe. 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, a nascent seafloor spreading center, is slowly rifting apart at a rate of 1–2 centimetres (0.3–0.8 in) per year. The immediate consequence of this is that there are (as of late 2005) a continuous sequence of earthquakes, fissures hundreds of metres long and deep appearing in the ground, and the valley floor sinking as much as 100 metres. Between September and October 2005, 163 earthquakes of magnitudes greater than 3.9 and a volcanic eruption occurred within the Afar rift. 2.5 cubic kilometers of molten rock was injected into the plate along a dyke between depths of 2 and 9 km, forcing open an 8 meter wide gap on the surface.[1]

Over millions of years, geologists expect the Red Sea to erode through the highlands surrounding the Afar Depression and flood the valley. In about 10 million years, geologists predict that the whole 6,000 km length of the East African Rift will be submerged, forming a new sea as large as the Red Sea is now. At that point, Africa will have lost its horn.[2]

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).

See also

Footnotes

1. ^ Wright, T.J.; et al. (July 2006). "Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode". Nature 442: 291-294. DOI:10.1038/nature04978. 
2. ^ Bojanowski 2006

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.
  • Bojanowski, Axel. "Africa's New Ocean: A Continent Splits Apart", Spiegel Online, March 15, 2006. Retrieved on 2006-03-16.  Includes a photo essay of the region and its geologic changes.

External links

Depression in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms, and may be referred to by a variety of technical terms.
  • A basin may be any large sediment filled depression.

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The Horn of Africa (alternatively Northeast Africa, and sometimes Somali Peninsula) is a peninsula of East Africa that juts for hundreds of kilometers into the Arabian Sea, and lies along the southern side of the Gulf of Aden.
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Anthem
Ertra, Ertra, Ertra


Capital
(and largest city) Asmara

Official languages none at national level
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Afar is one of the nine ethnic divisions (kililoch) of Ethiopia, and contains the homeland of the Afar people. Formerly known as Region 2, its current capital is Asayita; a new capital named Semera on the paved Awash - Asseb highway is under construction.
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Ethiopia (IPA: /i.θi.oʊ.pi.ə/) ( ʾĪtyōṗṗyā), officially the
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Anthem
Djibouti


Capital
(and largest city) Djibouti

Official languages Arabic and French
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A hominid is any member of the biological family Hominidae (the "great apes"), including the extinct and extant humans, chimpanzees, gorillas, and orangutans.
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The Middle Awash is an archaeological site along the Awash River in Ethiopia's Afar Depression. A number of Pleistocene and late Miocene hominid remains have been found at the site,[1] along with some of the oldest known Olduwan stone artifacts[2]
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Hadar (also spelled Adda Da'ar) is a village in Ethiopia, on the southern edge of the Afar Triangle, known for the nearby archeological site. It is located in Mille woreda, which is part of the Administrative Zone 1 of the Afar Region.
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A. afarensis

Binomial name
Australopithecus afarensis
Johanson & White, 1978

Australopithecus afarensis is an extinct hominid which lived between 3.9 and 2.9 million years ago.
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Location Afar Depression
Coordinates Coordinates:
Lake type crater lake

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State Party  Ethiopia
Type Cultural
Criteria ii, iii, iv
Reference 10
Region Africa

Inscription History
Inscription 1980  (4th Session)
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Salinity is the saltiness or dissolved salt content of a body of water. Salinity in Australian English and North American English may refer to salt in soil (see soil salination).

Definition


Water salinity
Fresh water Brackish water Saline water Brine
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State Party  Ethiopia
Type Cultural
Criteria ii, iii, iv
Reference 10
Region Africa

Inscription History
Inscription 1980  (4th Session)
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Afar (Afar alphabet Qafár, Ge'ez ዐፋር ʿāfār, Amh. translit. āfār, also spelled አፋር) are an ethnic group who reside principally in the Danakil Desert in the Afar Region of Ethiopia and in Eritrea and
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Red Sea is an inlet of the Indian Ocean between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb sound and the Gulf of Aden. In the north are the Sinai Peninsula, the Gulf of Aqaba) and the Gulf of Suez (leading to the Suez Canal).
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Salt is a mineral essential for animal life, composed primarily of sodium chloride. Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt.
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A biome is a major geographical area of ecologically similar communities of plants, animals, and soil organisms, often referred to as ecosystems. Biomes are defined based on factors such as plant structures (such as trees, shrubs, and grasses), leaf types (such as broadleaf and
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Deserts and xeric shrublands is a biome characterized by a dry climate. Deserts and xeric shrublands receive an annual average rainfall of ten inches or less, and have an arid or hyperarid climate, characterized by a strong moisture deficit, where annual potential loss of moisture
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Dracaena
Vand. ex L.

Species
See text

Dracaena is a genus of about 40 species of trees and succulent shrubs classified in the family Ruscaceae in the APG II system, or, according to some treatments, separated (with
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Herbivory is a form of predation in which an organism known as an herbivore, consumes principally autotrophs[1] such as plants, algae and photosynthesizing bacteria.
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E. grevyi

Binomial name
Equus grevyi
Oustalet, 1882

Range map


The Grevy's zebra (Equus grevyi), sometimes known as the imperial zebra
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GAZelle (Russian: ГАЗе́ль) is a series of mid-sized trucks, vans and buses made by Russian car manufacturer GAZ.
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O. beisa

Binomial name
Oryx beisa
Rüppell, 1835

The East African Oryx (Oryx beisa, also known as the Beisa Oryx) occurs in two subspecies, Beisa Oryx Oryx beisa beisa
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Struthionidae
Vigors, 1825

Genus: Struthio
Linnaeus, 1758

Species: S.
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endemic, it is unique to its own place or region; it is found only there, and not found naturally anywhere else. The place must be a discrete geographical unit, often an island or island group, but sometimes a country, habitat type, or other defined area or zone.
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Alaudidae

Genera
  • Mirafra
  • Pinarocorys
  • Heteromirafra
  • Certhilauda
  • Chersomanes
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Sagittariidae
R. Grandori & L. Grandori, 1935

Genus: Sagittarius
Hermann, 1783

Species: S.
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Otididae
Rafinesque, 1815

Genera

See text.

Bustards are large terrestrial birds mainly associated with dry open country and steppes in the Old World. They make up the family Otididae (formerly known as Otidae).
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