The Afar Triangle (also called the Afar Depression) is a
geological depression caused by the
Afar Triple Junction
The Afar Triple Junction (also called the Afro-Arabian Rift System) is located along a divergent plate boundary dividing the Nubian, Somali, and Arabian plates. This area is considered a present-day example of continental rifting leading to s ...
, which is part of the
Great Rift Valley
The Great Rift Valley is a series of contiguous geographic trenches, approximately in total length, that runs from Lebanon in Asia to Mozambique in Southeast Africa. While the name continues in some usages, it is rarely used in geology as it ...
in
East Africa
East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa:
Due to the historica ...
. The region has disclosed fossil specimens of the very earliest
hominins; that is, the earliest of the human clade, and it is thought by some paleontologists to be the cradle of the evolution of humans. The Depression overlaps the borders of
Eritrea
Eritrea ( ; ti, ኤርትራ, Ertra, ; ar, إرتريا, ʾIritriyā), officially the State of Eritrea, is a country in the Horn of Africa region of Eastern Africa, with its capital and largest city at Asmara. It is bordered by Ethiopi ...
,
Djibouti
Djibouti, ar, جيبوتي ', french: link=no, Djibouti, so, Jabuuti officially the Republic of Djibouti, is a country in the Horn of Africa, bordered by Somalia to the south, Ethiopia to the southwest, Eritrea in the north, and the Red ...
and the entire
Afar Region
The Afar Region (; aa, Qafar Rakaakayak; am, አፋር ክልል), formerly known as Region 2, is a regional state in northeastern Ethiopia and the homeland of the Afar people. Its capital is the planned city of Semera, which lies on the pave ...
of
Ethiopia
Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...
; and it contains the
lowest point in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
,
Lake Assal,
Djibouti
Djibouti, ar, جيبوتي ', french: link=no, Djibouti, so, Jabuuti officially the Republic of Djibouti, is a country in the Horn of Africa, bordered by Somalia to the south, Ethiopia to the southwest, Eritrea in the north, and the Red ...
, at below sea level.
The
Awash River
The Awash (sometimes spelled Awaash; Oromo: ''Awaash'', Amharic: አዋሽ, Afar: ''We'ayot'', Somali: ''Webiga Dir'') is a major river of Ethiopia. Its course is entirely contained within the boundaries of Ethiopia and empties into a chain of i ...
is the main waterflow into the region, but it runs dry during the annual dry season, and ends as a chain of
saline lakes
Saline may refer to:
* Saline (medicine), a liquid with salt content to match the human body
* Saline water, non-medicinal salt water
* Saline, a historical term (especially US) for a salt works or saltern
Places
* Saline, Calvados, a commune in ...
. The northern part of the Afar Depression is also known as the
Danakil Depression
The Danakil Depression is the northern part of the Afar Triangle or Afar Depression in Ethiopia, a geological depression that has resulted from the divergence of three tectonic plates in the Horn of Africa.
Geology
The Danakil Depression lie ...
. The lowlands are affected by heat,
drought
A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, an ...
, and minimal air circulation, and contain the hottest places (year-round average temperatures) of anywhere on Earth.
The Afar Triangle is bordered as follows (see the topographic map): on the west by the
Ethiopian Plateau
The Ethiopian Highlands is a rugged mass of mountains in Ethiopia in Northeast Africa. It forms the largest continuous area of its elevation in the continent, with little of its surface falling below , while the summits reach heights of up to . ...
and
escarpment
An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations.
The terms ''scarp'' and ''scarp face'' are often used interchangeably with ''esca ...
; to the north-east (between it and the Red Sea) by the
Danakil block; to the south by the Somali Plateau and escarpment; and to the south-east by the Ali-Sabieh block (adjoining the Somali Plateau).
Many important fossil localities exist in the Afar region, including the
Middle Awash region and the sites of
Hadar,
Dikika, and Woranso-Mille. These sites have produced specimens of the earliest (fossil) hominins and of human tool culture, as well as many fossils of various flora and fauna.
Environment
Dallol in the Danakil Depression is one of the hottest places year-round anywhere on Earth. There is no rain for most of the year; the yearly rainfall averages range from , with even less rain falling closer to the coast.
Daily mean temperatures at Dallol ranged from in January to in July in six years of observations from 1960 to 1966.
The
Awash River
The Awash (sometimes spelled Awaash; Oromo: ''Awaash'', Amharic: አዋሽ, Afar: ''We'ayot'', Somali: ''Webiga Dir'') is a major river of Ethiopia. Its course is entirely contained within the boundaries of Ethiopia and empties into a chain of i ...
, flowing north-eastward through the southern part of the Afar Region, provides a narrow green belt which enables life for the flora and fauna in the area and for the
Afars, the nomadic people living in the
Danakil Desert
The Danakil Desert is a desert in northeast Ethiopia, southern Eritrea, and northwestern Djibouti. Situated in the Afar Triangle, it stretches across of arid terrain. It is inhabited by a few Afar, who engage in salt mining. The area is known ...
. About from the
Red Sea
The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...
the Awash ends in a chain of salt lakes, where its waterflow evaporates as quickly as it is supplied. Some of the Afar Depression is covered by
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
deposits, and
mining salt is a major source of income for many Afar groups.
The Afar Depression
biome
A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
is characterized as
desert scrubland. Vegetation is mostly confined to
drought-resistant plants such as small trees (e.g. species of the
dragon tree
''Dracaena'' () is a genus of about 120 species of trees and succulent shrubs. The formerly accepted genera ''Pleomele'' and ''Sansevieria'' are now included in ''Dracaena''. In the APG IV classification system, it is placed in the famil ...
), shrubs, and grasses. Wildlife includes many
herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
s such as
Gr évy's zebra,
Soemmerring's gazelle
Soemmerring's gazelle (''Nanger soemmerringii''), also known as the Abyssinian mohr, is a gazelle species native to the Horn of Africa (Djibouti, Eritrea, Ethiopia, Somalia and South Sudan). The species was described and given its binomen by Ger ...
,
beisa and, notably, the last viable population of
African wild ass (''
Equus africanus somalicus'').
Birds include the
ostrich
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There ...
, the endemic
Archer's lark
Archer's lark (''Heteromirafra archeri''), also known as the Liben lark, is a species of lark in the family Alaudidae. It is found in Somalia, Somaliland and Ethiopia. Its natural habitats are subtropical or tropical dry shrubland and subtropical ...
, the
secretary bird
The secretarybird or secretary bird (''Sagittarius serpentarius'') is a large, mostly terrestrial bird of prey. Endemic to Africa, it is usually found in the open grasslands and savanna of the sub-Saharan region. John Frederick Miller describ ...
,
Arabian
The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plat ...
and
Kori bustards,
Abyssinian roller
The Abyssinian roller (''Coracias abyssinicus''), or Senegal roller, is a member of the roller family of birds which breeds across tropical Africa in a belt south of the Sahara, known as the Sahel. It is resident in the southern part of its rang ...
, and
crested francolin. In the southern part of the plain lies the
Mille-Serdo Wildlife Reserve.
The Afar Triangle is a cradle source of the earliest
hominin
The Hominini form a taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos) and in standard usage excludes the genus ''Gorilla'' (gorillas).
The ...
s. It contains a paleo-archaeological district that includes the
Middle Awash region and numerous prehistoric sites of fossil hominin discoveries, including: the
hominids
The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the ...
and possible hominins,
Ardi ARDI is the Access to Research for Development and Innovation program, a partnership between the World Intellectual Property Organization and major scientific and technical publishers. ARDI provides access to nearly 10,000 online journals, books an ...
, or ''
Ardipithecus ramidus
''Ardipithecus ramidus'' is a species of australopithecine from the Afar region of Early Pliocene Ethiopia 4.4 million years ago (mya). ''A. ramidus'', unlike modern hominids, has adaptations for both walking on two legs ( bipedality) and life i ...
'', and ''
Ardipithecus kadabba
''Ardipithecus kadabba'' is the scientific classification given to fossil remains "known only from teeth and bits and pieces of skeletal bones", originally estimated to be 5.8 to 5.2 million years old, and later revised to 5.77 to 5.54 million ye ...
'', see below; the
Gawis cranium
The Gawis cranium is a portion of a fossil hominin skull discovered on February 16, 2006 near the drainage of Gawis, a tributary of the Awash River in the Afar Depression, Ethiopia. Despite the presence of volcanic ash layers that are key to da ...
hominin from
Gona; several sites of the world's oldest stone tools;
Hadar, the site of
Lucy, the fossilized specimen of ''
Australopithecus afarensis
''Australopithecus afarensis'' is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa. The first fossils were discovered in the 1930s, but major fossil finds would no ...
''; and
Dikika, the site of the fossilized child
Selam, an
australopithecine
Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally ''Australopithecus'' ( cladistically including the genera ''Homo'', '' Paranthropus'', and ''Kenyanthropus''), and it typically inclu ...
hominin.
In 1994, near the Awash River in Ethiopia,
Tim D. White
Tim D. White (born August 24, 1950) is an American paleoanthropologist and Professor of Integrative Biology at the University of California, Berkeley. He is best known for leading the team which discovered Ardi, the type specimen of ''Ardipithecu ...
found the then-oldest known human ancestor: 4.4 million-year-old ''Ar. ramidus''. A fossilized almost complete skeleton of a female hominin which he named "Ardi", it took nearly 15 years to safely excavate, preserve, and describe the specimen and to prepare publication of the event.
Geology
The Afar Depression is the product of a
tectonic
Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...
triple-rifts junction (the
Afar Triple Junction
The Afar Triple Junction (also called the Afro-Arabian Rift System) is located along a divergent plate boundary dividing the Nubian, Somali, and Arabian plates. This area is considered a present-day example of continental rifting leading to s ...
), where the spreading ridges forming the
Red Sea
The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...
and the
Gulf of Aden
The Gulf of Aden ( ar, خليج عدن, so, Gacanka Cadmeed 𐒅𐒖𐒐𐒕𐒌 𐒋𐒖𐒆𐒗𐒒) is a deepwater gulf of the Indian Ocean between Yemen to the north, the Arabian Sea to the east, Djibouti to the west, and the Guardafui Chann ...
emerge on land and meet the
East African Rift
The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of ...
. The conjunction of these three plates of Earth's crust is near
Lake Abbe. The Afar Depression is one of two places on Earth where a
mid-ocean ridge
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a div ...
can be studied on land, the other being
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...
.
Within the triangle, the Earth's crust is slowly rifting apart at a rate of per year along each of the three
rift zones forming the "legs" of the triple junction. The immediate consequences are recurring sequences of earthquakes with deep fissures in the terrain hundreds of metres long, and the valley floor sinking broadly across the depression. During September and October 2005 some 163
earthquakes of magnitudes greater than 3.9 and a
volcanic eruption
Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are oft ...
occurred within the Afar rift at the
Dabbahu and
Erta Ale
Erta Ale (or Ertale or Irta'ale; Amharic: ኤርታሌ) is a continuously active basaltic shield volcano in the Afar Region of northeastern Ethiopia. It is situated in the Afar Depression, a barren desert area. Erta Ale is the most active volcano ...
volcanoes. Some 2.5 cubic kilometers of molten rock was injected from below into the plate along a
dyke between depths of , forcing open an wide gap on the surface, known as the
Dabbahu fissure.
Related eruptions have taken place in
Teru and
Aura
Aura most commonly refers to:
* Aura (paranormal), a field of luminous multicolored radiation around a person or object
* Aura (symptom), a symptom experienced before a migraine or seizure
Aura may also refer to:
Places Extraterrestrial
* 1488 ...
woredas
Districts of Ethiopia, also called woredas ( am, ወረዳ; ''woreda''), are the third level of the administrative divisions of Ethiopia – after '' zones'' and the '' regional states''.
These districts are further subdivided into a number of ...
. The rift has recently been recorded by means of three-dimensional laser mapping.
The region's salt deposits were created over time as water from the Red Sea periodically flooded the depression and evaporated; the most recent such flood was roughly 30,000 years ago.
Over the next millions of years, geologists expect erosion and the Red Sea to breach the highlands surrounding the Afar Depression and flood the valley. Geologists predict that in about 10 million years the whole length of the East African Rift will be submerged, forming a new ocean basin as large as today's Red Sea, and separating the
Somali Plate
The Somali Plate is a minor tectonic plate which straddles the Equator in the Eastern Hemisphere. It is currently in the process of separating from the African Plate along the East African Rift Valley. It is approximately centered on the isl ...
and the
Horn of Africa
The Horn of Africa (HoA), also known as the Somali Peninsula, is a large peninsula and geopolitical region in East Africa.Robert Stock, ''Africa South of the Sahara, Second Edition: A Geographical Interpretation'', (The Guilford Press; 2004 ...
from the rest of the continent.
The floor of the Afar Depression is composed of
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...
, mostly
basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
. One of Earth's five
lava lakes
Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified (someti ...
, Erta Ale is found here, as well as Dabbahu Volcano. It has been proposed that the Afar Depression is underlain by a
mantle plume
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hot ...
,
[Hammond, J. O. S., J.- M. Kendall, G. W. Stuart, C. J. Ebinger, I. D. Bastow, D. Keir, A. Ayele, M. Belachew, B. Goitom, G. Ogubazghi, and T. J. Wright. "Mantle Upwelling and Initiation of Rift Segmentation beneath the Afar Depression." Geology 41.6 (2013): 635–38. DOI:10.1130/G33925.1] a great upwelling of
mantle
A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that.
Mantle may refer to:
*Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear
**Mantle (vesture), an Eastern Orthodox ve ...
that melts to yield basalt as it approaches the surface.
See also
*
*
* in Djibouti
* ''(with link directory)''
* ''(with images)''
*The who inhabit the region
References
Citations
Sources
*
* Includes a photo essay of the region and its geologic changes.
*
*
* Jon Kalb: ''Adventures in the Bone Trade. The Race to Discover Human Ancestors in Ethiopia's Afar Depression.'' Copernicus Books, New York 2001,
*
External links
The Ethiopian state of Afar: Topography and Climate Photos of Afars and DanakilHuge collection of (3000) photos from different expeditions in the Dallol, Erta Ale and Danakil regions Photos of Afar Depression: between Ethiopia and Djibouti Web site of Main Ethiopian RiftScience news: Death of a Continent, Birth of an Ocean
{{Coord, 11.5, N, 41.0, E, display=title, source:frwiki
Landforms of Djibouti
Landforms of Eritrea
Landforms of Ethiopia
Afar Region
Cenozoic rifts and grabens
Landforms of Africa
Endorheic basins of Africa
Great Rift Valley