Afar Triangle

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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. EAfrica.png
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.
Topographic map showing the Afar Triangle, which correlates to the shaded area in the location map shown above Topographic30deg N0E30.png
Topographic map showing the Afar Triangle, which correlates to the shaded area in the location map shown above

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 Assal, Djibouti, at 155 m (or 509 ft) below sea level.

Contents

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.

Environment

MODIS satellite image of the Afar Depression and surrounding regions of the Red Sea, Gulf of Aden, Arabia, and the Horn of Africa AFAR-MODIS.jpg
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. Daily mean temperatures at Dallol ranged from 30 °C (86 °F) in January to 39 °C (102 °F) in July in six years of observations from 1960 to 1966; see climate of the lowlands of the Danakil Depression.

Perspective view of the Afar Depression and environs, generated by draping a Landsat image over a Digital elevation model. AfarDrape.jpg
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 Gawis cranium hominin from Gona; 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

A simplified geologic map of the Afar Depression. AfarGEOLOGY.jpg
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]

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

Related Research Articles

<i>Ardipithecus</i> Extinct genus of hominins

Ardipithecus is a genus of an extinct hominine that lived during the Late Miocene and Early Pliocene epochs in the Afar Depression, Ethiopia. Originally described as one of the earliest ancestors of humans after they diverged from the chimpanzees, the relation of this genus to human ancestors and whether it is a hominin is now a matter of debate. Two fossil species are described in the literature: A. ramidus, which lived about 4.4 million years ago during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago. Behavioral analysis showed that Ardipithecus could be very similar to chimpanzees, indicating that the early human ancestors were very chimpanzee-like in behavior.

Hadar, Ethiopia

Hadar is a paleontological site in Mille district, Administrative Zone 1 of the Afar Region, Ethiopia, some 15 km upstream (west) of the A1 road's bridge across the Awash River.

Danakil Desert desert in northeast Ethiopia

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. It is inhabited by a few Afar, who engage in salt mining. The area is known for its volcanoes and extreme heat, with daytime temperatures surpassing 50 °C (122 °F). Less than 25 mm (1 in) of rainfall occurs each year. The Danakil Desert is one of the lowest and hottest places on Earth.

Lake Karum

Lake Karum is a salt lake in the Afar Region of Ethiopia. One of two salt lakes in the northern end of the Danakil Depression, it lies at −120 m (−394 ft) relative to sea level. The volcano Erta Ale rises southwest of this lake.

Afar Region Region in Northeastern Ethiopia

Afar Region, 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 paved Awash–Assab highway.

Gawis cranium Hominin fossil

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 dating, the cranium is only generally dated between 200,000 and 500,000 years ago due to taphonomic issues.

The Middle Awash is a paleoanthropological research area in the Afar Region along the Awash River in Ethiopia's Afar Depression. It is a unique natural laboratory for the study of human origins and evolution and a number of fossils of the earliest hominins, particularly of the Australopithecines, as well as some of the oldest known Olduwan stone artifacts, have been found at the site—all of late Miocene, the Pliocene, and the very early Pleistocene times, that is, about 5.6 million years ago (mya) to 2.5 mya. It is broadly thought that the divergence of the lines of the earliest humans (hominins) and of chimpanzees (hominids) was completed near the beginning of that time range, or sometime between seven and five mya. However, the larger community of scientists provide several estimates for periods of divergence that imply a greater range for this event, see CHLCA: human-chimpanzee split.

Aramis is a village and archaeological site in north-eastern Ethiopia, where remains of Australopithecus and Ardipithecus have been found. The village is located in Administrative Zone 5 of the Afar Region, which is part of the Afar Sultanate of Dawe, with a latitude and longitude of 10°30′N40°30′E, and is part of the, Carri Rasuk, Xaale Faagê Daqaara.

Yohannes Haile-Selassie

Yohannes Haile-SelassieAmbaye is an Ethiopian paleoanthropologist. An authority on pre-Homo sapiens hominids, he particularly focuses his attention on the East African Rift and Middle Awash valleys.

Dallol, Ethiopia Place in Afar Region, Ethiopia

Dallol is a locality in the Dallol woreda of northern Ethiopia. Located in Administrative Zone 2 of the Afar Region in the Afar Depression, it has a latitude and longitude of 14°14′19″N40°17′38″E with an elevation of about 130 metres (430 ft) below sea level. The Central Statistical Agency has not published an estimate for the 2005 population of the village, which has been described as a ghost town.

Dallol (volcano) A cinder cone volcano in the Danakil Depression

Dallol is a cinder cone volcano in the Danakil Depression, northeast of the Erta Ale Range in Ethiopia. It was formed by the intrusion of basaltic magma into Miocene salt deposits and subsequent hydrothermal activity. Phreatic eruptions took place here in 1926, forming Dallol Volcano; numerous other eruption craters dot the salt flats nearby. These craters are the lowest known subaerial volcanic vents in the world, at 45 m (150 ft) or more below sea level. In October 2004 the shallow magma chamber beneath Dallol deflated and fed a magma intrusion southwards beneath the rift. The most recent signs of activity occurred in January 2011 in what may have been a degassing event from deep below the surface.

Erta Ale

Erta Ale is a continuously active basaltic shield volcano in the Afar Region of northeastern Ethiopia. It is situated in the Afar Depression, a badland desert area. Erta Ale is the most active volcano in Ethiopia.

<i>Ardipithecus kadabba</i> Hominin fossil

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 years old. According to the first description, these fossils are close to the common ancestor of chimps and humans. Their development lines are estimated to have parted 6.5–5.5 million years ago. It has been described as a "probable chronospecies" of A. ramidus. Although originally considered a subspecies of A. ramidus, in 2004 anthropologists Yohannes Haile-Selassie, Gen Suwa, and Tim D. White published an article elevating A. kadabba to species level on the basis of newly discovered teeth from Ethiopia. These teeth show "primitive morphology and wear pattern" which demonstrate that A. kadabba is a distinct species from A. ramidus.

<i>Ardipithecus ramidus</i> Extinct hominin from Early Pliocene Ethiopia

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 in the trees (arboreality). However, it would not have been as efficient at bipedality as humans, nor at arboreality as non-human great apes. Its discovery, along with Miocene apes, has reworked academic understanding of the chimpanzee-human last common ancestor from appearing much like modern day chimpanzees, orangutans and gorillas to being a creature without a modern anatomical cognate.

Dabbahu Volcano

Dabbahu Volcano is an active volcano located in the remote Afar Region of Ethiopia. This stratovolcano is part of the Afar Triangle, 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.

Danakil Depression Geological depression, northern part of the Afar Triangle or Afar Depression in Ethiopia

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.

Jon Kalb

Jon Kalb August 17, 1941 - October 27, 2017 was a research geologist with the Vertebrate Paleontology Laboratory, University of Texas at Austin. He received a pre-doctoral fellowship from the Carnegie Geophysical Laboratory in 1968, a graduate fellowship from Johns Hopkins University in 1969, and a BSc from American University in 1970.

Derek Keir has been an associate professor of geophysics at the University of Southampton since 2015. In 2013 he received the Bullerwell Lecture award from the British Geophysical Association (BGA) for significant contributions to geophysics.

The Middle Awash Project is an international research expedition conducted in the Afar region of Ethiopia with the goal of determining the origins of humanity. The project has the approval of the Ethiopian Culture Ministry and a strong commitment to developing Ethiopian archaeology, paleontology and geology research infrastructure. This project has discovered over 260 fossil specimens and over 17,000 vertebrate fossil specimens to date ranging from 200,000 to 6,000,000 years in age. Researchers have discovered the remains of four hominin species, the earliest subspecies of homo sapiens as well as stone tools. All specimens are permanently held at the National Museum of Ethiopia, where the project’s laboratory work is conducted year round.

Dallol (hydrothermal system)

Dallol is a unique, terrestrial hydrothermal system in Ethiopia. It is known for its unearthly colors and mineral patterns, and the very acidic fluids that discharge from its hydrothermal springs.

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" (PDF). Science. 326 (5949): 75–86. Bibcode:2009Sci...326...75W. doi:10.1126/science.1175802. PMID   19810190. S2CID   20189444. Archived from the original (PDF) on 2019-02-27.
  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" (PDF). Nature. 442 (7100): 291–294. Bibcode:2006Natur.442..291W. doi:10.1038/nature04978. hdl: 2158/1078052 . PMID   16855588. S2CID   4319443.
  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, Axel (2006-03-15). "Africa's New Ocean: A Continent Splits Apart". Spiegel Online. Retrieved 2006-03-16. Includes a photo essay of the region and its geologic changes. }}
  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

Coordinates: 11°30′N41°00′E / 11.5°N 41.0°E / 11.5; 41.0