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{{Short description|Geological depression caused by the Afar triple junction}}
[[File:Topographic30deg N0E30.png|thumb|upright=1.4|Topographic map showing the 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 (geographical concept)|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. The Depression overlaps the borders of [[Eritrea]], [[Djibouti]] and the entire [[Afar (region)|Afar Region]] of [[Ethiopia]]; and it contains the [[List of places on land with elevations below sea level|lowest point]] in [[Africa]], [[Lake Assal (Djibouti)|Lake Assal]], [[Djibouti]], at {{Convert|155|m|ft|abbr=on|sp=us}} 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 [[Salt lake|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 Highlands|Ethiopian Plateau]] and [[escarpment]]; to the north-east (between it and the Red Sea) by the [[Danakil Alps|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).<ref>{{cite web |url= http://www.see.leeds.ac.uk/afar/new-afar/geology-afar/structure-tech-pages/geol-afar-dep-tech.html |title=Geology of the Afar Depression |publisher=Afar Rift Consortium |access-date=27 October 2013}}</ref>
Many important fossil localities exist in the Afar region, including the [[Middle Awash]] region and the sites of [[Hadar, Ethiopia|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==
[[File:ET_Afar_asv2018-01_img52_Dallol.jpg|thumb|Landscape in Dallol]]
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|salt mining]] is still a major source of income for many Afar tribes. ▼
[[Dallol, Ethiopia|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 {{Convert|100 to 200|mm|in|abbr=on|sp=us|sigfig=1}}, with even less rain falling closer to the coast. [[Dallol, Ethiopia#Climate|Daily mean temperatures at Dallol]] ranged from {{Convert|30|°C|°F}} in January to {{Convert|39|°C|°F|0}} in July in six years of observations from 1960 to 1966.
[[
▲
The Afar Depression [[biome]] is characterized as [[Deserts and xeric shrublands|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 [[ungulate]]s including [[Grevy's Zebra]], [[Gazelle|Soemmering’s Gazelle]], [[East African Oryx|Oryx Beisa ]] and, notably, the last viable population of [[Donkey|African wild ass]] (''Equus africanus somalicus''). Birds include the [[ostrich]], the [[endemic (ecology)|endemic]] Archer's [[lark]] (''Heteromirafra archeri''), the [[Secretary Bird]], Arabian and Kori [[bustard]]s, [[Abyssinian Roller]] and [[Francolin|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 [[hominid]]s but also elephantoids, crocodiles and hippopotamus.▼
▲The Afar Depression [[biome]] is characterized as [[Deserts and xeric shrublands|desert scrubland]]. Vegetation is mostly confined to [[Xerophyte|drought-resistant plants]] such as small trees (e.g. species of the [[dragon tree]]), shrubs, and grasses. Wildlife includes many [[
Birds include the [[ostrich]], the endemic [[Archer's lark]], the [[secretary bird]], [[Arabian bustard|Arabian]] and [[Kori bustard]]s, [[Abyssinian roller]], 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]]s. 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, Ethiopia|Gona]]; several sites of the world's oldest stone tools; [[Hadar, Ethiopia|Hadar]], the site of [[Lucy (Australopithecus)|Lucy]], the fossilized specimen of ''[[Australopithecus afarensis]]''; and [[Dikika]], the site of the fossilized child [[Selam (Australopithecus)|Selam]], an [[australopithecine]] hominin.<ref>{{cite journal |last=Shreeve |first=Jamie |date=July 2010 |title=The Evolutionary Road |url=http://ngm.nationalgeographic.com/2010/07/middle-awash/shreeve-text |archive-url=https://web.archive.org/web/20100619130007/http://ngm.nationalgeographic.com/2010/07/middle-awash/shreeve-text |url-status=dead |archive-date=June 19, 2010 |journal=[[National Geographic (magazine)|National Geographic]] |___location=Washington, D.C. |publisher=[[National Geographic Society]] |issn=0027-9358 |access-date=2015-05-28}}</ref>
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.<ref>{{cite journal | last1 = White | first1 = Tim D. | last2 = Asfaw | first2 = Berhane | last3 = Beyene | first3 = Yonas | last4 = Haile-Selassie | first4 = Yohannes | last5 = Lovejoy | first5 = C. Owen | last6 = Suwa | first6 = Gen | last7 = WoldeGabrie | first7 = Giday | year = 2009 | title = Ardipithecus ramidus and the Paleobiology of Early Hominids. | url = http://pdfs.semanticscholar.org/82b9/e80c26a5f783c793b4e5c4b7e95e478abb21.pdf | archive-url = https://web.archive.org/web/20190227152736/http://pdfs.semanticscholar.org/82b9/e80c26a5f783c793b4e5c4b7e95e478abb21.pdf | url-status = dead | archive-date = 2019-02-27 | journal = Science | volume = 326 | issue = 5949| pages = 75–86 | doi = 10.1126/science.1175802 | pmid = 19810190 | bibcode = 2009Sci...326...75W | s2cid = 20189444 }}</ref>
==Geology==
[[File:Tectonic African Arabian Rift System.jpg|thumb|Tectonic map of the [[Great Rift Valley|African-Arabian Rift System]]. The Afar Depression is situated at the junction of the [[Red Sea Rift|Red Sea]], the [[Gulf of Aden]], and the [[East African Rift|East African Rift System]]]]
[[File:Tectonic map of the Afar Depression.jpg|thumb|Tectonic map of the Afar Depression showing the small scale [[Plate tectonics|plate]] configuration, the velocities of extension and the active [[rift]] segments.]]
[[File:Geological map of the Afar Depression.jpg|thumb|[[Geological map]] of the Afar Depression showing the [[Igneous rock|magmatic rocks]] from old (yellow) to recent (dark red), as well as the [[Fault (geology)|fault]] pattern. ]]
The Afar Depression is a [[plate tectonics|tectonic]] [[triple junction#Examples|triple junction]] (the [[Afar triple junction]]), where the spreading ridges of the [[Red Sea Rift|Red Sea]] and the [[Gulf of Aden]] meet the [[Great Rift Valley|East African Rift]]. These rifts are caused by the northeastward movement of the [[Arabian plate]] (approximately 20 mm/yr<ref>{{Cite journal |last1=Viltres |first1=Renier |last2=Jónsson |first2=Sigurjón |last3=Alothman |first3=Abdulaziz O. |last4=Liu |first4=Shaozhuo |last5=Leroy |first5=Sylvie |last6=Masson |first6=Frédéric |last7=Doubre |first7=Cécile |last8=Reilinger |first8=Robert |date=2022 |title=Present-Day Motion of the Arabian Plate |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021TC007013 |journal=Tectonics |language=en |volume=41 |issue=3 |pages=e2021TC007013 |doi=10.1029/2021TC007013 |bibcode=2022Tecto..4107013V |issn=1944-9194}}</ref>) and the much slower eastward movement of the [[Somali plate|Somalian plate]] (approximately 5 mm/yr<ref>{{Cite journal |last1=Stamps |first1=D.S. |last2=Kreemer |first2=C. |last3=Fernandes |first3=R. |last4=Rajaonarison |first4=T.A. |last5=Rambolamanana |first5=G. |date=2021-09-23 |title=Redefining East African Rift System kinematics |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/49/2/150/591119/Redefining-East-African-Rift-System-kinematics?redirectedFrom=fulltext |journal=Geology |volume=49 |issue=2 |pages=150–155 |doi=10.1130/G47985.1 |bibcode=2021Geo....49..150S |issn=0091-7613|url-access=subscription }}</ref>) relative to the [[African plate|Nubian (African) plate]].
At smaller scale, the [[tectonics]] of the Afar Depression is more complex. An independent [[Microplate (geology)|microplate]], the [[Danakil microplate|Danakil (or Arrata) microplate]], is carrying a piece of continental material (the Danakil block) between the Afar and the Red Sea and is rotating counterclockwise,<ref name=":8">{{Cite book |last=Varet |first=Jacques |url=http://link.springer.com/10.1007/978-3-319-60865-5 |title=Geology of Afar (East Africa) |date=2018 |publisher=Springer International Publishing |isbn=978-3-319-60863-1 |series=Regional Geology Reviews |___location=Cham |doi=10.1007/978-3-319-60865-5|bibcode=2018geaf.book.....V }}</ref><ref>{{Cite journal |last1=Viltres |first1=Renier |last2=Jónsson |first2=Sigurjón |last3=Ruch |first3=Joël |last4=Doubre |first4=Cécile |last5=Reilinger |first5=Robert |last6=Floyd |first6=Michael |last7=Ogubazghi |first7=Ghebrebrhan |date=2020-06-01 |title=Kinematics and deformation of the southern Red Sea region from GPS observations |url=https://academic.oup.com/gji/article/221/3/2143/5800989 |journal=Geophysical Journal International |language=en |volume=221 |issue=3 |pages=2143–2154 |doi=10.1093/gji/ggaa109 |doi-access=free |issn=0956-540X}}</ref><ref name=":0">{{Cite journal |last1=Rime |first1=Valentin |last2=Foubert |first2=Anneleen |last3=Ruch |first3=Joël |last4=Kidane |first4=Tesfaye |date=2023-09-01 |title=Tectonostratigraphic evolution and significance of the Afar Depression |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825223002088 |journal=Earth-Science Reviews |volume=244 |pages=104519 |doi=10.1016/j.earscirev.2023.104519 |bibcode=2023ESRv..24404519R |issn=0012-8252|doi-access=free }}</ref> causing the slow propagation of the Afar Rift to the north and the propagation of the Red Sea rift to the south.<ref name=":0" />
The recent geological history of the Afar Depression started around 33 million years ago, before any [[rifting]], with the eruption of the Ethiopian [[Flood basalt|Flood Basalts]] that covered large parts of [[Ethiopia]] and [[Yemen]] with hundreds to thousands of meters of [[Volcanic rock|volcanic rocks]].<ref>{{Cite journal |last1=Hofmann |first1=C. |last2=Courtillot |first2=V. |last3=Féraud |first3=G. |last4=Rochette |first4=P. |last5=Yirgu |first5=G. |last6=Ketefo |first6=E. |last7=Pik |first7=R. |date=October 1997 |title=Timing of the Ethiopian flood basalt event and implications for plume birth and global change |url=https://www.nature.com/articles/39853 |journal=Nature |language=en |volume=389 |issue=6653 |pages=838–841 |doi=10.1038/39853 |bibcode=1997Natur.389..838H |issn=1476-4687|url-access=subscription }}</ref><ref>{{Cite journal |last1=Baker |first1=Joel |last2=Snee |first2=Lawrence |last3=Menzies |first3=Martin |date=1996-02-01 |title=A brief Oligocene period of flood volcanism in Yemen: implications for the duration and rate of continental flood volcanism at the Afro-Arabian triple junction |url=https://linkinghub.elsevier.com/retrieve/pii/0012821X95002296 |journal=Earth and Planetary Science Letters |volume=138 |issue=1 |pages=39–55 |doi=10.1016/0012-821X(95)00229-6 |bibcode=1996E&PSL.138...39B |issn=0012-821X|url-access=subscription }}</ref><ref>{{Citation |last1=Mohr |first1=Paul |title=The Ethiopian Flood Basalt Province |date=1988 |work=Continental Flood Basalts |pages=63–110 |editor-last=Macdougall |editor-first=J. D. |url=https://link.springer.com/chapter/10.1007/978-94-015-7805-9_3 |access-date=2025-05-16 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-015-7805-9_3 |isbn=978-94-015-7805-9 |last2=Zanettin |first2=Bruno|url-access=subscription }}</ref><ref>{{Cite journal |last1=Coulié |first1=E |last2=Quidelleur |first2=X |last3=Gillot |first3=P. -Y |last4=Courtillot |first4=V |last5=Lefèvre |first5=J. -C |last6=Chiesa |first6=S |date=2003-02-15 |title=Comparative K–Ar and Ar/Ar dating of Ethiopian and Yemenite Oligocene volcanism: implications for timing and duration of the Ethiopian traps |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X02010890 |journal=Earth and Planetary Science Letters |volume=206 |issue=3 |pages=477–492 |doi=10.1016/S0012-821X(02)01089-0 |bibcode=2003E&PSL.206..477C |issn=0012-821X|url-access=subscription }}</ref><ref>{{Cite journal |last=Rooney |first=Tyrone O. |date=2017-08-01 |title=The Cenozoic magmatism of East-Africa: Part I — Flood basalts and pulsed magmatism |url=https://linkinghub.elsevier.com/retrieve/pii/S0024493717301883 |journal=Lithos |volume=286-287 |pages=264–301 |doi=10.1016/j.lithos.2017.05.014 |bibcode=2017Litho.286..264R |issn=0024-4937|doi-access=free }}</ref> These eruptions were caused by a hot rising [[mantle plume]] that impacted the [[continental crust]] and produced large quantities of [[magma]].<ref>{{Cite journal |last1=Hansen |first1=Samantha E. |last2=Nyblade |first2=Andrew A. |last3=Benoit |first3=Margaret H. |date=2012-02-15 |title=Mantle structure beneath Africa and Arabia from adaptively parameterized P-wave tomography: Implications for the origin of Cenozoic Afro-Arabian tectonism |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X11007436 |journal=Earth and Planetary Science Letters |volume=319-320 |pages=23–34 |doi=10.1016/j.epsl.2011.12.023 |bibcode=2012E&PSL.319...23H |issn=0012-821X|url-access=subscription }}</ref><ref>{{Cite journal |last1=Civiero |first1=Chiara |last2=Lebedev |first2=Sergei |last3=Celli |first3=Nicolas L. |date=2022 |title=A Complex Mantle Plume Head Below East Africa-Arabia Shaped by the Lithosphere-Asthenosphere Boundary Topography |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GC010610 |journal=Geochemistry, Geophysics, Geosystems |language=en |volume=23 |issue=11 |pages=e2022GC010610 |doi=10.1029/2022GC010610 |bibcode=2022GGG....2310610C |issn=1525-2027|hdl=10261/286934 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Rooney |first1=Tyrone O. |last2=Herzberg |first2=Claude |last3=Bastow |first3=Ian D. |date=2012-01-01 |title=Elevated mantle temperature beneath East Africa |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/40/1/27/130670/Elevated-mantle-temperature-beneath-East-Africa?redirectedFrom=fulltext |journal=Geology |volume=40 |issue=1 |pages=27–30 |doi=10.1130/G32382.1 |bibcode=2012Geo....40...27R |issn=0091-7613|url-access=subscription }}</ref><ref>{{Cite journal |last1=Civiero |first1=Chiara |last2=Celli |first2=Nicolas L. |last3=Tesauro |first3=Magdala |date=2023-12-01 |title=Revisiting the geodynamics of the Middle East region from an integrated geophysical perspective |url=https://linkinghub.elsevier.com/retrieve/pii/S0264370723000455 |journal=Journal of Geodynamics |volume=158 |pages=102005 |doi=10.1016/j.jog.2023.102005 |bibcode=2023JGeo..15802005C |issn=0264-3707|hdl=11368/3066862 |hdl-access=free }}</ref> This impact of the mantle plume also caused the [[Dynamic topography|high topography]] of the region,<ref>{{Cite journal |last1=Moucha |first1=Robert |last2=Forte |first2=Alessandro M. |date=October 2011 |title=Changes in African topography driven by mantle convection |url=https://www.nature.com/articles/ngeo1235 |journal=Nature Geoscience |language=en |volume=4 |issue=10 |pages=707–712 |doi=10.1038/ngeo1235 |bibcode=2011NatGe...4..707M |issn=1752-0908|url-access=subscription }}</ref><ref>{{Cite journal |last1=Sembroni |first1=Andrea |last2=Faccenna |first2=Claudio |last3=Becker |first3=Thorsten W. |last4=Molin |first4=Paola |date=2024-10-01 |title=The uplift of the East Africa - Arabia swell |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825224002289 |journal=Earth-Science Reviews |volume=257 |pages=104901 |doi=10.1016/j.earscirev.2024.104901 |bibcode=2024ESRv..25704901S |issn=0012-8252|doi-access=free }}</ref> an effect still visible today.
This [[Volcanism|volcanic activity]] weakened the crust and allowed the beginning of the separation between the Arabian plate and the Nubian plate.<ref>{{Cite journal |last1=Bellahsen |first1=N. |last2=Faccenna |first2=C. |last3=Funiciello |first3=F. |last4=Daniel |first4=J. M. |last5=Jolivet |first5=L. |date=2003-11-30 |title=Why did Arabia separate from Africa? Insights from 3-D laboratory experiments |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X03005168 |journal=Earth and Planetary Science Letters |volume=216 |issue=3 |pages=365–381 |doi=10.1016/S0012-821X(03)00516-8 |bibcode=2003E&PSL.216..365B |issn=0012-821X|url-access=subscription }}</ref><ref>{{Cite journal |last1=Koptev |first1=Alexander |last2=Gerya |first2=Taras |last3=Calais |first3=Eric |last4=Leroy |first4=Sylvie |last5=Burov |first5=Evgueni |date=2018-10-03 |title=Afar triple junction triggered by plume-assisted bi-directional continental break-up |journal=Scientific Reports |language=en |volume=8 |issue=1 |pages=14742 |doi=10.1038/s41598-018-33117-3 |issn=2045-2322 |pmc=6170478 |pmid=30283091|bibcode=2018NatSR...814742K }}</ref> The Gulf of Aden rift propagated westwards and rifting started in the Afar region approximately 28 million years ago, at the same time as in the southern Red Sea.<ref name=":0" /> Between 13 and 8 Ma, a major reorganization of the region took place.<ref name=":0" /> The [[Danakil microplate]] started rotating, causing the secession of tectonic activity in the [[Bab-el-Mandeb|southernmost Red Sea]], and propagation of the Afar rift in the [[Danakil Depression]] (i.e. the northern part of the Afar Triangle).<ref name=":0" /> At the same time, the [[Great Rift Valley, Ethiopia|Main Ethiopian Rift]] (the northernmost part of the [[East African Rift|East African Rift System]]) started to form and the Afar Depression became a [[triple junction]].<ref>{{Cite journal |last1=Wolfenden |first1=Ellen |last2=Ebinger |first2=Cynthia |last3=Yirgu |first3=Gezahegn |last4=Deino |first4=Alan |last5=Ayalew |first5=Dereje |date=2004-07-30 |title=Evolution of the northern Main Ethiopian rift: birth of a triple junction |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X04002705 |journal=Earth and Planetary Science Letters |volume=224 |issue=1 |pages=213–228 |doi=10.1016/j.epsl.2004.04.022 |bibcode=2004E&PSL.224..213W |issn=0012-821X|url-access=subscription }}</ref> This movement in three different directions by three major [[List of tectonic plates|plates]] caused extension and thinning of the crust, explaining the general morphology of the Afar Depression.
During the [[Extensional tectonics|extension]], [[volcanism]] remained very important in the Depression, with kilometers of [[Volcanic rock|volcanic rocks]] dominated by [[Basalt|basalts]] emplaced in central Afar.<ref name=":8" /><ref>{{Cite journal |last1=Lahitte |first1=Pierre |last2=Gillot |first2=Pierre-Yves |last3=Kidane |first3=Tesfaye |last4=Courtillot |first4=Vincent |last5=Bekele |first5=Abebe |date=2003 |title=New age constraints on the timing of volcanism in central Afar, in the presence of propagating rifts |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2001JB001689 |journal=Journal of Geophysical Research: Solid Earth |language=en |volume=108 |issue=B2 |page=2123 |doi=10.1029/2001JB001689 |bibcode=2003JGRB..108.2123L |issn=2156-2202}}</ref><ref>{{Cite journal |last=Rooney |first=Tyrone O. |date=2020-05-01 |title=The Cenozoic magmatism of East Africa: Part IV – The terminal stages of rifting preserved in the Northern East African Rift System |url=https://linkinghub.elsevier.com/retrieve/pii/S0024493720300189 |journal=Lithos |volume=360-361 |pages=105381 |doi=10.1016/j.lithos.2020.105381 |bibcode=2020Litho.36005381R |issn=0024-4937|doi-access=free }}</ref> So much magmatic rocks were added to crust, at the surface as lava flows, but also in the crust as [[Igneous intrusion|intrusions]] and below the crust as [[Magmatic underplating|underplated]] material, that it did not thin as much as expected.<ref name=":0" /><ref name=":1">{{Cite journal |last1=Rime |first1=Valentin |last2=Keir |first2=Derek |last3=Phethean |first3=Jordan |last4=Kidane |first4=Tesfaye |last5=Foubert |first5=Anneleen |date=2024-07-31 |title=Central Afar: An analogue for oceanic plateau development |url=https://pubs.geoscienceworld.org/gsa/geology/article/52/11/819/646098/Central-Afar-An-analogue-for-oceanic-plateau |journal=Geology |volume=52 |issue=11 |pages=819–824 |doi=10.1130/G52330.1 |bibcode=2024Geo....52..819R |issn=0091-7613|hdl=2158/1408188 |hdl-access=free }}</ref><ref name=":6">{{Cite journal |last=Stab |first=Martin |last2=Bellahsen |first2=Nicolas |last3=Pik |first3=Raphaël |last4=Quidelleur |first4=Xavier |last5=Ayalew |first5=Dereje |last6=Leroy |first6=Sylvie |date=2016 |title=Modes of rifting in magma-rich settings: Tectono-magmatic evolution of Central Afar |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2015TC003893 |journal=Tectonics |language=en |volume=35 |issue=1 |pages=2–38 |doi=10.1002/2015TC003893 |issn=1944-9194}}</ref> This phenomenon is called ''magma-compensated thinning''<ref>{{Cite journal |last1=Thybo |first1=H. |last2=Nielsen |first2=C. A. |date=February 2009 |title=Magma-compensated crustal thinning in continental rift zones |url=https://www.nature.com/articles/nature07688 |journal=Nature |language=en |volume=457 |issue=7231 |pages=873–876 |doi=10.1038/nature07688 |bibcode=2009Natur.457..873T |issn=1476-4687|url-access=subscription }}</ref> and it can explain why the central Afar is the only part of the Gulf of Aden - Red Sea system that do not feature normal [[oceanic crust]].<ref name=":0" /><ref name=":1" /> Because of this high volcanic activity, some researchers propose that this region might never form a normal ocean, but instead form an [[oceanic plateau]], similar to [[Iceland]].<ref name=":1" />
[[File:Graben Afar ASTER 20020327.jpg|thumb|left|Satellite image of a [[graben]] in the Afar Depression.]]
[[Volcanism|Volcanic]] and [[Tectonics|tectonic]] activity is still very strong in the Depression. In different regions of the Afar, the extension is accommodated by [[Fault (geology)|faulting]] or [[Igneous intrusion|magmatic intrusions]].<ref name=":2">{{Cite journal |last1=Ebinger |first1=Cynthia |last2=Ayele |first2=Atalay |last3=Keir |first3=Derek |last4=Rowland |first4=Julie |last5=Yirgu |first5=Gezahegn |last6=Wright |first6=Tim |last7=Belachew |first7=Manahloh |last8=Hamling |first8=Ian |date=2010-05-30 |title=Length and Timescales of Rift Faulting and Magma Intrusion: The Afar Rifting Cycle from 2005 to Present |url=https://www.annualreviews.org/content/journals/10.1146/annurev-earth-040809-152333 |journal=Annual Review of Earth and Planetary Sciences |language=en |volume=38 |issue= |pages=439–466 |bibcode=2010AREPS..38..439E |doi=10.1146/annurev-earth-040809-152333 |issn=0084-6597|hdl=2158/1110108 |hdl-access=free }}</ref><ref name=":7" /> The faults form a complex system of [[Horst (geology)|horst]] and [[graben]]<ref>{{Cite journal |last1=Polun |first1=Sean G. |last2=Gomez |first2=Francisco |last3=Tesfaye |first3=Samson |date=2018-10-01 |title=Scaling properties of normal faults in the central Afar, Ethiopia and Djibouti: Implications for strain partitioning during the final stages of continental breakup |url=https://linkinghub.elsevier.com/retrieve/pii/S0191814118302748 |journal=Journal of Structural Geology |volume=115 |pages=178–189 |doi=10.1016/j.jsg.2018.07.018 |bibcode=2018JSG...115..178P |issn=0191-8141|url-access=subscription }}</ref><ref name=":7">{{Cite journal |last1=La Rosa |first1=Alessandro |last2=Gayrin |first2=Pauline |last3=Brune |first3=Sascha |last4=Pagli |first4=Carolina |last5=Muluneh |first5=Ameha A. |last6=Tortelli |first6=Gianmaria |last7=Keir |first7=Derek |date=2025-03-26 |title=Cross-scale strain analysis in the Afar rift (East Africa) from automatic fault mapping and geodesy |url=https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1215/ |journal=EGUsphere |language=English |pages=1–28 |doi=10.5194/egusphere-2025-1215|doi-access=free }}</ref><ref name=":6" /><ref>{{Cite journal |last=Chauvet |first=François |last2=Geoffroy |first2=Laurent |last3=Le Gall |first3=Bernard |last4=Jaud |first4=Marion |date=2023-05-01 |title=Volcanic passive margins and break-up processes in the southern Red Sea |url=https://linkinghub.elsevier.com/retrieve/pii/S1342937X23000266 |journal=Gondwana Research |volume=117 |pages=169–193 |doi=10.1016/j.gr.2023.01.004 |issn=1342-937X}}</ref> easily observable on [[Orthophoto|orthophotos]] thanks to the [[Desert|desertic environment]]. [[Igneous intrusion|Magmatic intrusions]] intrude the crust as [[Dike (geology)|dikes]] that can also erupt at the surface.<ref name=":2" /><ref name=":3">{{Cite journal |last1=Ayele |first1=Atalay |last2=Keir |first2=Derek |last3=Ebinger |first3=Cynthia |last4=Wright |first4=Tim J. |last5=Stuart |first5=Graham W. |last6=Buck |first6=W. Roger |last7=Jacques |first7=Eric |last8=Ogubazghi |first8=Ghebrebrhan |last9=Sholan |first9=Jamal |date=2009 |title=September 2005 mega-dike emplacement in the Manda-Harraro nascent oceanic rift (Afar depression) |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2009GL039605 |journal=Geophysical Research Letters |language=en |volume=36 |issue=20 |doi=10.1029/2009GL039605 |bibcode=2009GeoRL..3620306A |issn=1944-8007|hdl=2158/1110101 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Keir |first1=Derek |last2=Pagli |first2=Carolina |last3=Bastow |first3=Ian D. |last4=Ayele |first4=Atalay |date=2011 |title=The magma-assisted removal of Arabia in Afar: Evidence from dike injection in the Ethiopian rift captured using InSAR and seismicity |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2010TC002785 |journal=Tectonics |language=en |volume=30 |issue=2 |doi=10.1029/2010TC002785 |bibcode=2011Tecto..30.2008K |issn=1944-9194|hdl=11568/500499 |hdl-access=free }}</ref> Both processes cause important [[Earthquake|earthquakes]] reaching magnitude 6<ref>{{Cite journal |last=Hofstetter |first=R. |last2=Beyth |first2=M. |date=2003-11-01 |title=The Afar Depression: interpretation of the 1960–2000 earthquakes |url=https://academic.oup.com/gji/article/155/2/715/599878 |journal=Geophysical Journal International |volume=155 |issue=2 |pages=715–732 |doi=10.1046/j.1365-246X.2003.02080.x |issn=0956-540X}}</ref> and having devastating consequences for the local population.<ref>{{Cite book |last=Gouin |first=P |title=Earthquake History of Ethiopia and the Horn of Africa |date=1979 |publisher=IDRC |___location=Ottawa, ON, CA}}</ref> In 2005, an important magmatic and tectonic crisis in [[Dabbahu Volcano|Dabbahu]] caused up to 8 meters of extension along a 60 km rift segment and the [[Igneous intrusion|intrusion]] of 2.5 km<sup>3</sup> of lava in only two weeks.<ref>{{Cite journal |last1=Wright |first1=Tim J. |last2=Ebinger |first2=Cindy |last3=Biggs |first3=Juliet |last4=Ayele |first4=Atalay |last5=Yirgu |first5=Gezahegn |last6=Keir |first6=Derek |last7=Stork |first7=Anna |date=July 2006 |title=Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode |url=https://www.nature.com/articles/nature04978 |journal=Nature |language=en |volume=442 |issue=7100 |pages=291–294 |doi=10.1038/nature04978 |pmid=16855588 |bibcode=2006Natur.442..291W |hdl=2158/1078052 |issn=1476-4687|hdl-access=free }}</ref><ref name=":2" /><ref name=":3" /> Accounting for an extension rate of approx. 20 mm/yr in the area, 8 m of extension corresponds to the release of 400 years of [[Stress (mechanics)|stress]] accumulation in the [[Crust (geology)|crust]].
In the northern part of the Afar Depression, called the [[Danakil Depression]], the volcanic activity was less intense until approx. 0.6 My ago.<ref name=":0" /> This allowed the crust to thin more than the central part of the Afar and the topography to reach elevations below sea level.<ref name=":0" /> This allowed the Red Sea to invade the Danakil Depression during at least four [[Interglacial|periods of high sea-level]] in the [[Pleistocene]].<ref name=":4">{{Cite journal |last1=Jaramillo-Vogel |first1=David |last2=Foubert |first2=Anneleen |last3=Braga |first3=Juan Carlos |last4=Schaegis |first4=Jean-Charles |last5=Atnafu |first5=Balemwal |last6=Grobety |first6=Bernard |last7=Kidane |first7=Tesfaye |date=2019 |title=Pleistocene sea-floor fibrous crusts and spherulites in the Danakil Depression (Afar, Ethiopia) |url=https://onlinelibrary.wiley.com/doi/10.1111/sed.12484 |journal=Sedimentology |language=en |volume=66 |issue=2 |pages=480–512 |doi=10.1111/sed.12484 |bibcode=2019Sedim..66..480J |issn=1365-3091|url-access=subscription }}</ref><ref name=":5">{{Cite journal |last1=Foubert |first1=Anneleen |last2=Keir |first2=Derek |last3=Atnafu |first3=Balemwal |last4=Kidane |first4=Tesfaye |last5=the ADD-ON Workshop Consortium |date=2024-08-30 |title=Workshop report: Afar Dallol Drilling – ONset of sedimentary processes in an active rift basin (ADD-ON) |url=https://sd.copernicus.org/articles/33/207/2024/ |journal=Scientific Drilling |language=English |volume=33 |issue=2 |pages=207–218 |doi=10.5194/sd-33-207-2024 |doi-access=free |bibcode=2024SciDr..33..207F |issn=1816-8957|hdl=20.500.11850/693510 |hdl-access=free }}</ref> The last flooding happened approx. 130'000 years ago.<ref name=":4" /><ref name=":5" /> These flooding are testified by fossil [[Coral reef|coral reefs]]<ref name=":4" /><ref name=":5" /> and by thick (>500 m) [[Evaporite|evaporites]] deposits (mainly [[halite]], i.e. [[salt]]) found in the central part of the basin.<ref>{{Cite journal |last1=Holwerda |first1=James G. |last2=Hutchinson |first2=Richard W. |date=1968-03-01 |title=Potash-bearing evaporites in the Danakil area, Ethiopia |url=http://pubs.geoscienceworld.org/economicgeology/article/63/2/124/17788/Potashbearing-evaporites-in-the-Danakil-area |journal=Economic Geology |language=en |volume=63 |issue=2 |pages=124–150 |doi=10.2113/gsecongeo.63.2.124 |bibcode=1968EcGeo..63..124H |issn=1554-0774}}</ref><ref>{{Cite journal |last1=Rime |first1=Valentin |last2=Negga |first2=Haileyesus |last3=Fentimen |first3=Robin |last4=Rüggeberg |first4=Andres |last5=El Korh |first5=Afifé |last6=Pirkenseer |first6=Claudius |last7=Schaegis |first7=Jean-Charles |last8=Hajdas |first8=Irka |last9=Adatte |first9=Thierry |last10=Atnafu |first10=Balemwal |last11=Kidane |first11=Tesfaye |last12=Foubert |first12=Anneleen |date=2025 |title=Nature and significance of Late Pleistocene to Holocene thick evaporite deposits of the Danakil Depression, Afar, Ethiopia |url=https://onlinelibrary.wiley.com/doi/10.1111/sed.13237 |journal=Sedimentology |language=en |volume=72 |issue=2 |pages=475–506 |doi=10.1111/sed.13237 |bibcode=2025Sedim..72..475R |issn=1365-3091}}</ref>
Geologists predict that in about 10 million years the whole {{Convert|6000|km|mi|abbr=on|sp=us|sigfig=2}} length of the East African Rift will be submerged, forming a new [[Oceanic basin|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.<ref>{{cite news | first=Axel | last=Bojanowski | title=Africa's New Ocean: A Continent Splits Apart | date=2006-03-15 | publisher=Spiegel Online | url = http://www.spiegel.de/international/spiegel/0,1518,405947,00.html | access-date=2006-03-16 }} Includes a photo essay of the region and its geologic changes.
</ref>
==See also==
*{{annotated link|Dallol (volcano)|Dallol}}
*{{annotated link|Horst (geology)|Horst}}
*{{annotated link|Lake Assal (Djibouti)|Lake Assal}} in Djibouti
*{{annotated link|List of fossil sites}} ''(with link directory)''
*{{annotated link|List of human evolution fossils|List of hominini (hominin) fossils}} ''(with images)''
*The {{annotated link|Afar people}} who inhabit the region
==References==
===Citations===
{{Reflist}}
==
{{Refbegin}}
*{{Cite journal |last1=Barberi |first1=F. |last2=Borsi |first2=S. |last3=Ferrara |first3=G. |last4=Marinelli |first4=G. |last5=Santacroce |first5=R. |last6=Tazieff |first6=H. |last7=Varet |first7=J. |title=Evolution of the Danakil Depression (Afar, Ethiopia) in Light of Radiometric Age Determinations |journal=Journal of Geology |volume=80 |issue=6 |year=1972 |pages=720–729 |doi=10.1086/627797 |bibcode=1972JG.....80..720B|s2cid=128757919 }}
*Kloos, Helmut (1982) 'Development, drought and famine in the Awash valley of Ethiopia', ''African Studies Review'', vol. 25, no. 4, p. 21-48.▼
*{{cite news | first=Axel | last=Bojanowski | title=Africa's New Ocean: A Continent Splits Apart | date=2006-03-15 | publisher=Spiegel Online | url = http://www.spiegel.de/international/spiegel/0,1518,405947,00.html | access-date=2006-03-16 }} Includes a photo essay of the region and its geologic changes.
▲*{{Cite journal |last=Kloos
*{{WWF ecoregion|name=Ethiopian xeric grasslands and shrublands|id=at1305}}
*Jon Kalb: ''Adventures in the Bone Trade. The Race to Discover Human Ancestors in Ethiopia's Afar Depression.'' Copernicus Books, New York 2001, {{ISBN|0-387-98742-8 }}
*{{cite book |last1=Jeangene Vilmer |first1=Jean-Baptiste |last2=Gouery |first2=Franck |title=Les Afars d'Éthiopie. Dans l'enfer du Danakil |url = http://www.afars-danakil.fr |year=2011 |publisher=Non lieu |isbn=9782352701088 |url-status=dead |archive-url = https://web.archive.org/web/20130731230922/http://www.afars-danakil.fr/ |archive-date=2013-07-31 }}
{{Refend}}
*[https://web.archive.org/web/20080928202802/http://www.ethiopar.net/type/English/basinfo/infoafar.htm#TopClimate The Ethiopian state of Afar: Topography and Climate]▼
*{{in lang|fr}} [https://web.archive.org/web/20130731230922/http://www.afars-danakil.fr/ Photos of Afars and Danakil]
*{{in lang|fr}} [https://web.archive.org/web/20010623195328/http://www.erta-ale.org/photos_volcan.html Photos of Erta Ale, Hotsprings at Dallol and Danakil]▼
*{{in lang|de}} [http://www.volcanodiscovery.com/en/index.php?id=1514&L=1 Huge collection of (3000) photos from different expeditions in the Dallol, Erta Ale and Danakil regions]
*{{in lang|fr}} [http://danakil.ethiopia.free.fr Photos of Afar Depression: between Ethiopia and Djibouti]
*{{in lang|en}} [http://ethiopianrift.igg.cnr.it Web site of Main Ethiopian Rift]
*[https://web.archive.org/web/20121001154553/http://www.sciencenews.org/view/feature/id/331389/title/Death_of_a_Continent,Birth_of_an_Ocean Science news: Death of a Continent, Birth of an Ocean]
{{Major African geological formations}}
▲== External links ==
{{Regions of Africa}}
{{Authority control}}
▲*[http://www.erta-ale.org/photos_volcan.html Photos of Erta Ale]
▲*[http://www.ethiopar.net/English/basinfo/infoafar.htm#TopClimate The Ethiopian state of Afar]
{{Coord|11.5|N|41.0|E|display=title|source:frwiki}}
[[Category:Geography of Djibouti]]▼
[[Category:Geography of Eritrea]]▼
[[Category:Geography of Ethiopia]]▼
[[Category:Depressions]]▼
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[[Category:Cenozoic rifts and grabens]]
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