Afar Triangle: Difference between revisions

{{Short description|Geological depression caused by the Afar Triple Junction [[Afar Triangle Democratic Republic State]]}}

[[File:EAfricaTectonical map of East Africa.png|thumb|upright=1.4|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.]]

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; see [[Middle Awash]], [[Hadar, Ethiopia|Hadar]]. 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 (or 509 |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 [[saltSalt 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) [[hominin]]shominins and of human tool culture, as well as many fossils of various flora and fauna.

[[File:AFAR-MODIS.jpg|thumb|[[MODIS|Moderate Resolution Imaging Spectroradiometer]] satellite image of the Afar Depression and surrounding regions of the [[Red Sea]], [[Gulf of Aden]], [[Arabia]], and the [[Horn of Africa]]]]

[[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 millimetres (4&nbsp;to&nbsp;7&nbsp;|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; ''see'' [[Dallol, Ethiopia#Climate|climate of the lowlands of the Danakil Depression]].

[[File:AfarDrape.jpg|thumb|left|Perspective view of the Afar Depression and environs, generated by draping a [[Landsat]] image over a [[Digitaldigital elevation model]].]]

Within the Triangletriangle, the Earth's crust is slowly rifting apart at a rate of {{Convert|1–2 centimetres (0.4–0.8&nbsp;|cm|in)|abbr=on|sp=us|sigfig=1}} per year along each of the three [[Rift zone|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 Depressiondepression. During September and October 2005 some 163 [[Seismic magnitude scales|earthquakes of magnitudes]] greater than 3.9 and a [[volcanic eruption]] occurred within the Afar rift at the [[Dabbahu Volcano|Dabbahu]] and [[Erta Ale]] volcanoes. Some 2.5 cubic kilometers of molten rock was injected from below into the plate along a [[Dike (geology)|dyke]] between depths of {{Convert|2 and 9&nbsp;|km|mi|abbr=on|sp=us|sigfig=1}}, forcing open an {{Convert|8 meter|m|ft|abbr=on|sp=us}} wide gap on the surface, known as the [[Dabbahu fissure]].<ref>{{cite journal |date=July 2006 | title = Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode | journal = Nature | volume = 442 | pages = 291–294 | doi = 10.1038/nature04978 | pmid = 16855588 | last1 = Wright | first1 = TJ | last2 = Ebinger | first2 = C | last3 = Biggs | first3 = J | last4 = Ayele | first4 = A | last5 = Yirgu | first5 = G | last6 = Keir | first6 = D | last7 = Stork | first7 = A | issue = 7100| bibcode = 2006Natur.442..291W | hdl = 2158/1078052 | s2cid = 4319443 | url = https://flore.unifi.it/bitstream/2158/1078052/1/nature04978.pdf | hdl-access = free }}</ref><ref>{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/7950845.stm|title=Inside the Hottest Place on Earth|work=[[BBC News]]|access-date=August 30, 2009 | date=2009-03-19}}</ref>

The region's salt deposits were created over time as water from the Red Sea periodically flooded the Depressiondepression and evaporated; the most recent such flood was roughly 30,000 years ago.<ref name="natgeo2012">{{cite journal

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 {{Convert|6,000&nbsp;|km|mi|abbr=on|sp=us|sigfig=2}} 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 platePlate]] 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.

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]],<ref>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</ref> a great upwelling of [[mantle (geology)|mantle]] that melts to yield basalt as it approaches the surface.

* {{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 }}