Afar Triangle

The Afar Triangle (also called the Afar Depression) is a geological depression caused by the Afar Triple Junction, which is part of the Great Rift Valley in East Africa. 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, see Middle Awash, Hadar. The Depression overlaps the borders of Eritrea, Djibouti and the entire Afar Region of Ethiopia; and it contains the lowest point in Africa, Lake Asal, Djibouti, at 155 m (or 509 ft) below sea level.

The Awash River is the main waterflow into the region, but it runs dry during the annual dry season, and ends as a chain of saline lakes. The northern part of the Afar Depression is also known as the Danakil Depression. The lowlands are affected by heat, drought, 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 and escarpment; 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).[1]

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.

Coordinates: 11°30′N 41°00′E / 11.5°N 41.0°E

EAfrica
Location map of the Afar Triangle (the shaded area in the center of the map) and the East African Rift zones; red triangles show historically active volcanoes.
Topographic30deg N0E30
Topographic map showing the Afar Triangle, which correlates to the shaded area in the location map shown above

Environment

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

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 100 to 200 millimetres (4 to 7 in), with even less rain falling closer to the coast. The climate varies from around 25 °C (77 °F) during the very short rainy season (November–February) to 48 °C (118 °F) during the dry season (February–November); see climate of the lowlands of the Danakil Depression.

AfarDrape
Perspective view of the Afar Depression and environs, generated by draping a Landsat image over a Digital elevation model.

The Awash River, 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. About 128 kilometres (80 mi) from the Red Sea the Awash ends in a chain of salt lakes, where its waterflow evaporates as quickly as it is supplied. Some 1,200 km2 (460 sq mi) of the Afar Depression is covered by salt deposits, and mining salt is a major source of income for many Afar groups.

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, 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 lies the Mille-Sardo Wildlife Reserve in Ethiopia.

The Afar Triangle is a cradle source of the earliest hominins. It contains a paleo-archaeological district that includes the Middle Awash region and numerous prehistoric sites of fossil hominin discoveries, including: the hominids and possible hominins, Ardi, or Ardipithecus ramidus, and Ardipithecus kadabba, see below; the Gona (Gawis cranium) hominin; several sites of the world's oldest stone tools; Hadar, the site of Lucy, the fossilized specimen of Australopithecus afarensis; and Dikika, the site of the fossilized child Selam, an australopithecine hominin.[2]

In 1994, near the Awash River in Ethiopia, Tim D. White 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.[3]

Geology

AfarGEOLOGY
A simplified geologic map of the Afar Depression.

The Afar Depression is the product of a tectonic triple-rifts junction (the Afar Triple Junction), where the spreading ridges forming the Red Sea and the Gulf of Aden emerge on land and meet the East African Rift. 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 can be studied on land, the other being Iceland.[4]

Within the Triangle, the Earth's crust is slowly rifting apart at a rate of 1–2 centimetres (0.4–0.8 in) 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 occurred within the Afar rift at the Dabbahu and Erta Ale volcanoes. Some 2.5 cubic kilometers of molten rock was injected from below into the plate along a dyke between depths of 2 and 9 km, forcing open an 8 meter wide gap on the surface, known as the Dabbahu fissure.[5][6]

Graben Afar ASTER 20020327
Satellite image of a graben in the Afar Depression.

Related eruptions have taken place in Teru and Aura woredas. The rift has recently been recorded by means of three-dimensional laser mapping.[7]

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.[8] 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 6,000 km 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 and the Horn of Africa from the rest of the continent.[9]

The floor of the Afar Depression is composed of lava, mostly basalt. One of Earth's five lava lakes, Erta Ale is found here, as well as Dabbahu Volcano. It has been proposed that the Afar Depression is underlain by a mantle plume,[10] a great upwelling of mantle that melts to yield basalt as it approaches the surface.

See also

References

Citations

  1. ^ "Geology of the Afar Depression". Afar Rift Consortium. Retrieved 27 October 2013.
  2. ^ Shreeve, Jamie (July 2010). "The Evolutionary Road". National Geographic. Washington, D.C.: National Geographic Society. ISSN 0027-9358. Retrieved 2015-05-28.
  3. ^ White, Tim D.; Asfaw, Berhane; Beyene, Yonas; Haile-Selassie, Yohannes; Lovejoy, C. Owen; Suwa, Gen; WoldeGabrie, Giday (2009). "Ardipithecus ramidus and the Paleobiology of Early Hominids". Science. 326 (5949): 75–86. Bibcode:2009Sci...326...75W. doi:10.1126/science.1175802. PMID 19810190.
  4. ^ Beyene, Alebachew & Abdelsalam, Mohamed G. (2005). "Tectonics of the Afar Depression: A review and synthesis". Journal of African Earth Sciences. 41 (1–2): 41–59. Bibcode:2005JAfES..41...41B. doi:10.1016/j.jafrearsci.2005.03.003.
  5. ^ Wright, TJ; Ebinger, C; Biggs, J; Ayele, A; Yirgu, G; Keir, D; Stork, A (July 2006). "Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode". Nature. 442 (7100): 291–294. Bibcode:2006Natur.442..291W. doi:10.1038/nature04978. PMID 16855588.
  6. ^ "Inside the Hottest Place on Earth". BBC News. 2009-03-19. Retrieved August 30, 2009.
  7. ^ Hottest Place On Earth, Episode 1 at bbc.co.uk Archived November 14, 2012, at the Wayback Machine
  8. ^ Morell, Virginia (January 2012). "Hyperactive Zone". National Geographic. 221 (1): 116–127.
  9. ^ Bojanowski 2006
  10. ^ 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

Sources

External links

AL 333

AL 333, commonly referred to as the "First Family", is a collection of prehistoric hominid teeth and bones. Discovered in 1975 by Donald Johanson's team in Hadar, Ethiopia, the "First Family" is estimated to be about 3.2 million years old, and consists of the remains of at least thirteen individuals of different ages. They are generally thought to be members of the species Australopithecus afarensis. There are multiple theories about the hominids’ cause of death and some debate over their species and sexual dimorphism.

Afar Region

The Afar Regional State (Afar: Qafar; Amharic: አፋር ክልል) is one of the nine regional states (kililoch) of Ethiopia, and is the homeland of the Afar people. Formerly known as Region 2, its new capital as of 2007 is the recently constructed city of Semera, which lies on the paved Awash–Assab highway.

The Afar Triangle, the northern part of which is the Danakil Depression, is part of the Great Rift Valley of Ethiopia, and is located in the north of the region. It has the lowest point in Ethiopia and one of the lowest in Africa. The southern part of the region consists of the valley of the Awash River, which empties into a string of lakes along the Ethiopian-Djibouti border. Other notable landmarks include the Awash and Yangudi Rassa National Parks.

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 seafloor spreading and producing an oceanic basin. Here, the Red Sea Rift meets the Aden Ridge and the East African Rift. It extends a total of 6,500 kilometers (4,000 mi) in three arms from the Afar Triangle to Mozambique.The connecting three arms form a triple junction. The northern most branching arm extends North through the Red Sea and into the Dead Sea, while the eastern arm extends through the Gulf of Aden and connects to the Mid-Indian Ocean ridge further to the east. Both of these rifting arms are below sea level and are similar to a mid-ocean ridge.The third rifting arm runs south extending around 4000 km through the countries of Kenya, Uganda, the Democratic Republic of Congo, Rwanda, Burundi, Tanzania, Zambia, Malawi and, finally, Mozambique. This southern rifting arm is better known as the East African Rift or the East African Rift System (EARS), when it includes the Afar Triangle.

African Plate

The African Plate is a major tectonic plate straddling the equator as well as the prime meridian. It includes much of the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges. Between 60 million years ago and 10 million years ago, the Somali Plate began rifting from the African Plate along the East African Rift. Since the continent of Africa consists of crust from both the African and the Somali plates, some literature refers to the African Plate as the Nubian Plate to distinguish it from the continent as a whole.

Australopithecus deyiremeda

Australopithecus deyiremeda is a proposed species of early hominin among those who lived about 3.5–3.3 million years ago in northern Ethiopia, around the same time and place as several discovered specimens of Australopithecus afarensis, including the well-known "Lucy".

The discoverers believe A. deyiremeda is a new species. If true, some fossils identified as A. afarensis may more properly belong to A. deyiremeda. Some anthropologists have suggested that the identification of A. deyiremeda as a new species requires more evidence than has been obtained thus far.

Dabbahu Volcano

Dabbahu Volcano (also Boina, Boyna or Moina) is an active volcano located in the remote Afar Region of Ethiopia. This stratovolcano is part of the Afar Triangle (Afar Depression), a highly active volcanic region which includes Erta Ale. An eruption on September 26, 2005 created a large fissure in the ground, known as the Dabbahu fissure.

Dams and reservoirs in Ethiopia

Ethiopia is called the water tower of Africa due to its combination of mountainous areas with a comparatively large share of water resources in Africa. Only a fraction of this potential has been harnessed so far, 1% at the beginning of the 21st century.. In order to become the powerhouse of Africa, Ethiopia is actively exploiting its water resources by building dams, reservoirs, irrigation and diversion canals and hydropower stations. The benefits of the dams are not only limited to hydropower. Many dams are multi-purpose dams that are also designed to provide water for irrigation, drinking water and flood control. However, hydropower is expected to be the main benefit of the dams.

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.

Danakil Desert

The Danakil Desert is a desert in northeast Ethiopia, southern Eritrea, and northwestern Djibouti. Situated in the Afar Triangle, it stretches across 136,956 square kilometres (52,879 sq mi) of arid terrain. The area is known for its volcanoes and extreme heat, with daytime temperatures surpassing 50 °C (122 °F). Less than an inch of rainfall occurs each year. The Danakil Desert is one of the lowest and hottest places on Earth. It is inhabited by a few Afar, who engage in salt mining.

Donald Johanson

Donald Carl Johanson (born June 28, 1943) is an American paleoanthropologist. He is known for discovering – with Yves Coppens and Maurice Taieb – the fossil of a female hominin australopithecine known as "Lucy" in the Afar Triangle region of Hadar, Ethiopia.

El Djouf

El Djouf (Arabic: الجوف‎) is a desert, an arid natural region of sand dunes and rock salt which covers northeastern Mauritania and part of northwestern Mali. El Djouf is a part of the Sahara Desert in the north.

A meteorite of a rare type of carbonaceous chondrite was found in el Djouf in October 1989.

Hadar, Ethiopia

Hadar (also spelled Qad daqar; Afar "white [qidi] stream [daqar]") is a village in Ethiopia on the southern edge of the Afar Triangle (part of East Africa's Great Rift Valley). The village is known for the nearby archaeological digs which have yielded some of the most well-known hominin fossils, including "Lucy."

According to Jon Kalb, early maps show caravan routes passing within 10 or 15 kilometers of Hadar, though not through it. The British explorer L.M. Nesbitt passed 15 kilometers west of Hadar in 1928.

Lake Assal (Djibouti)

Lake Assal (Arabic: بحيرة عسل‎ Buḥayrah ʿAsal, literally 'honey lake') is a crater lake in central-western Djibouti. It is located at the western end of Gulf of Tadjoura in the Tadjoura Region, touching Dikhil Region, at the top of the Great Rift Valley, some 120 km (75 mi) west of Djibouti city. Lake Assal is a saline lake which lies 155 m (509 ft) below sea level in the Afar Triangle, making it the lowest point on land in Africa and the third-lowest point on Earth after the Sea of Galilee and the Dead Sea. No outflow occurs from the lake, and due to high evaporation, the salinity level of its waters is 10 times that of the sea, making it the third most saline body of water in the world behind Don Juan Pond and Gaet'ale Pond. Lake Assal is the world's largest salt reserve, which is exploited under four concessions awarded in 2002 at the southeast end of the lake; the major share of production (nearly 80%) is held by Société d’Exploitation du Lac and Société d’Exploitation du Salt Investment S.A de Djibouti. It is situated approximately 109 kilometres (68 miles) west of the nation's capital Djibouti City.

The lake, considered a "national treasure", is a protected zone under the law No. 45/AN/04/5L of the National Environmental Action Plan, 2000. However, the law does not define the boundary limits of the lake. Since the exploitation of the salt from the lake was uncontrolled, the Plan has emphasized the need for managing the exploitation to avoid negative impact on the lake environment. The Government of Djibouti has initiated a proposal with UNESCO to declare the Lake Assal zone and the Ardoukoba volcano as a World Heritage Site.

Lucy (Australopithecus)

Lucy is the common name of AL 288-1, several hundred pieces of bone fossils representing 40 percent of the skeleton of a female of the hominin species Australopithecus afarensis. In Ethiopia, the assembly is also known as Dinkinesh, which means "you are marvelous" in the Amharic language. Lucy was discovered in 1974 in Africa, near the village Hadar in the Awash Valley of the Afar Triangle in Ethiopia, by paleoanthropologist Donald Johanson of the Cleveland Museum of Natural History.The Lucy specimen is an early australopithecine and is dated to about 3.2 million years ago. The skeleton presents a small skull akin to that of non-hominin apes, plus evidence of a walking-gait that was bipedal and upright, akin to that of humans (and other hominins); this combination supports the view of human evolution that bipedalism preceded increase in brain size. A 2016 study proposes that Australopithecus afarensis was also to a large extent tree-dwelling, though the extent of this is debated."Lucy" acquired her name from the song "Lucy in the Sky with Diamonds" by The Beatles, which was played loudly and repeatedly in the expedition camp all evening after the excavation team's first day of work on the recovery site. After public announcement of the discovery, Lucy captured much public interest, becoming a household name at the time.

Lucy became famous worldwide, and the story of her discovery and reconstruction was published in a book by Johanson. Beginning in 2007, the fossil assembly and associated artifacts were exhibited publicly in an extended six-year tour of the United States; the exhibition was called Lucy's Legacy: The Hidden Treasures of Ethiopia. There was discussion of the risks of damage to the unique fossils, and other museums preferred to display casts of the fossil assembly. The original fossils were returned to Ethiopia in 2013, and subsequent exhibitions have used casts.

Mount Alayta

Mount Alayta is a shield volcano in the Afar Region of Ethiopia. Part of the Afar Triangle (Afar Depression), a highly active volcanic region which includes the adjacent Mount Afdera, this volcano covers an area of 2700 square kilometers southwest of Lake Afrera. A chain of younger craters are aligned along a north-northwest axis in the basaltic-to-trachytic shield along the east side of the shield volcano, which extends to the western flank of Mount Afdera. The Alayta Lavafeld covered by fresh lava streams was formed from a series of north-south fissures. In two areas on the southern side of the volcanic complex, fumaroles can be observed.Two historical eruptions that were formerly attributed to Mount Afdera are believed to have originated from Alayta. One of those eruptions, between June and August 1907, produced a large lava flow from a vent on its southeastern flank. Its most recent eruption was in 1915.

Oldowan

The Oldowan (or Mode I) is the earliest widespread stone tool archaeological industry (style) in prehistory. These early tools were simple, usually made with one or a few flakes chipped off with another stone. Oldowan tools were used during the Lower Paleolithic period, 2.6 million years ago up until 1.7 million years ago, by ancient Hominin (early humans) across much of Africa, South Asia, the Middle East and Europe. This technological industry was followed by the more sophisticated Acheulean industry.

Oldowan is pre-dated by Lomekwian tools at a single site dated to 3.3 mya (million years ago). It is not clear if the Lomekwian industry bears any relation to the Oldowan.The term Oldowan is taken from the site of Olduvai Gorge in Tanzania, where the first Oldowan lithics were discovered by the archaeologist Louis Leakey in the 1930s. However, some contemporary archaeologists and palaeoanthropologists prefer to use the term Mode 1 tools to designate pebble tool industries (including Oldowan), with Mode 2 designating bifacially worked tools (including Acheulean handaxes), Mode 3 designating prepared-core tools, and so forth.Classification of Oldowan tools is still somewhat contentious. Mary Leakey was the first to create a system to classify Oldowan assemblages, and built her system based on prescribed use. The system included choppers, scrapers, and pounders. However, more recent classifications of Oldowan assemblages have been made that focus primarily on manufacture due to the problematic nature of assuming use from stone artefacts. An example is Isaac et al.'s tri-modal categories of "Flaked Pieces" (cores/choppers), "Detached Pieces" (flakes and fragments), "Pounded Pieces" (cobbles utilized as hammerstones, etc.) and "Unmodified Pieces" (manuports, stones transported to sites). Oldowan tools are sometimes called "pebble tools", so named because the blanks chosen for their production already resemble, in pebble form, the final product.It is not known for sure which hominin species created and used Oldowan tools. Its emergence is often associated with the species Australopithecus garhi and its flourishing with early species of Homo such as H. habilis and H. ergaster. Early Homo erectus appears to inherit Oldowan technology and refines it into the Acheulean industry beginning 1.7 million years ago.

Piacenzian

The Piacenzian is in the international geologic time scale the upper stage or latest age of the Pliocene. It spans the time between 3.6 ± 0.005 Ma and 2.588 ± 0.005 Ma (million years ago). The Piacenzian is after the Zanclean and is followed by the Gelasian (part of the Pleistocene).

The Piacenzian is roughly coeval with the European land mammal age MN 16, overlaps the late Chapadmalalan and early Uquian South American land mammal age and falls inside the more extensive Blancan North American land mammal age. It also correlates with the Astian, Redonian, Reuverian and Romanian regional stages of Europe. Some authorities describe the British Red Crag Formation and Waltonian stage as late Piacenzian, while others regard them as early Pleistocene.

Tindouf Basin

The Tindouf Basin is a major sedimentary basin in West Africa, to the south of the little Atlas region, Morocco. It stretches from west to east about 700 kilometres (430 mi) and covers about 100,000 square kilometres (39,000 sq mi), mostly in Algeria but with a western extension into Morocco and Western Sahara.

Major African geological formations
Plates
Cratons and shields
Shear zones
Orogens
Rifts
Sedimentary basins
Mountain ranges
Regions of Africa
Central Africa
East Africa
North Africa
West Africa
Southern Africa
Macro-regions

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