{{short description|Active continental rift zone in East Africa}} {{Use dmy dates|date=December 2022}} [[File:Tectonical map of East Africa.png|thumb|upright=1.35|A map of [[East Africa]] showing some of the historically active volcanoes (as red triangles) and the [[Afar Triangle]] (shaded at the center), which is a so-called triple junction (or triple point) where three plates are pulling away from one another: the Arabian plate and two parts of the [[African plate]]—the Nubian and [[Somali plate|Somali]]—splitting along the East African Rift Zone]] [[File:East Africa Rift System GPS and stresses.png|thumb|Main rift faults, plates, plate boundaries, GPS plate velocities between adjacent blocks and minimum horizontal stress directions]]
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.<ref>{{cite journal |last1=Ebinger |first1=Cynthia |author-link1=Cynthia Ebinger |title=Continental break-up: The East African perspective |journal=Astronomy and Geophysics |date=April 2005 |volume=46 |issue=2 |pages=2.16–2.21 |doi=10.1111/j.1468-4004.2005.46216.x |doi-access=free}}</ref> It is considered to be part of a larger system, formerly known as the [[Great Rift Valley]], that extends north to [[Asia Minor]], also known as Anatolia.
A narrow zone, the rift is a developing [[divergent boundary|divergent]] [[tectonic plate]] [[list of tectonic plate interactions|boundary]] where the [[African plate]] is in the process of splitting into two tectonic plates, called the [[Somali plate]] and the [[Nubian plate]], at a rate of {{convert|8|–|9|mm|abbr=on}} per year.<ref>{{cite journal |last1=Fernandes |first1=R.M.S. |last2=Ambrosius |first2=B.A.C. |last3=Noomen |first3=R. |last4=Bastos |first4=L. |last5=Combrinck |first5=L. |last6=Miranda |first6=J.M. |last7=Spakman |first7=W. |title=Angular velocities of Nubia and Somalia from continuous GPS data: implications on present-day relative kinematics |journal=[[Earth and Planetary Science Letters]] |year=2004 |volume=222 |issue=1 |pages=197–208 |doi=10.1016/j.epsl.2004.02.008 |bibcode=2004E&PSL.222..197F}}</ref> The rift system consists of three [[List of tectonic plates#Microplates|microplate]]s, the [[Victoria microplate]] to the north, and the [[Rovuma plate|Rovuma]] and [[Lwandle plate|Lwandle]] microplates to the south. The Victoria microplate is rotating anti-clockwise with respect to the African plate. Its rotation is caused by the configuration of mechanically weaker and stronger lithospheric regions in the EARS.<ref>{{cite web|last=Osborne|first=Hannah|date=9 June 2020|url=https://www.newsweek.com/one-africas-tectonic-plates-rotating-different-direction-all-others-1509682 |title=One of Africa's Tectonic Plates Is Rotating in a Different Direction to All the Others|publisher=[[Newsweek]]}}</ref><ref>GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre (8 June 2020) [https://www.sciencedaily.com/releases/2020/06/200608092937.htm "Why the Victoria Plate in Africa rotates"] ''[[Science Daily]]''</ref>
Many of the [[African Great Lakes]] lie within the Rift Valley.
== Extent == A series of distinct rift basins, the East African Rift System extends over thousands of kilometers.<ref name="corti-erv">{{cite web |last=Corti |first=G |title=The Ethiopian Rift Valley |url=https://ethiopianrift.cnr.it/home-eng/ |publisher=National Research Council of Italy, Institute of Geosciences and Earth Resources |date=2026-02-15 |access-date=2026-02-16}}</ref> North of the [[Afar triple junction]], the rift follows two paths: west to the [[Red Sea Rift]] and east to the [[Aden Ridge]] in the [[Gulf of Aden]].
Southward from the Afar triple junction, the EAR consists of two main branches. The Eastern Rift Valley (also known as [[Gregory Rift]]) includes the [[Main Ethiopian Rift]], runs southward from the Afar triple junction, and continues south as the Kenyan Rift Valley,<ref name="moungenot">{{cite journal |last1=Mougenot |first1=D. |last2=Recq |first2=M. |last3=Virlogeux |first3=P. |last4=Lepvrier |first4=C. |title=Seaward extension of the East African Rift |journal=Nature |date=June 1986 |volume=321 |issue=6070 |pages=599–603 |doi=10.1038/321599a0 |bibcode=1986Natur.321..599M |s2cid=4282682}}</ref> into northern Tanzania. The Western Rift Valley includes the [[Albertine Rift]], which transects [[Democratic Republic of the Congo]], [[Uganda]], [[Rwanda]], and [[Burundi]] through the [[Ruzizi Plain]], and farther south [[Tanzania]], [[Zambia]], the valley of [[Lake Malawi]] and [[Mozambique]].<ref>{{cite journal |last=Chorowicz |first=Jean |year=2005 |title=The East African rift system |journal=Journal of African Earth Sciences |volume=43 |issue=1 |pages=379–410 |bibcode=2005JAfES..43..379C |doi=10.1016/j.jafrearsci.2005.07.019}}</ref>
The rift also continues offshore from the coast of Mozambique along the Kerimba and Lacerda [[grabens]], which are joined by the Davie Ridge, a {{convert|2200|km||-long|abbr=on|adj=mid}} relic fracture zone that cuts across the West Somali basin, straddling the boundary between Tanzania and Mozambique.<ref name="moungenot" /> The Davie Ridge ranges between {{convert|30–120|km||abbr=on}} wide, with a west-facing scarp (east-plunging arch) along the southern half of its length that rises to {{convert|2300|m||abbr=on}} above the sea floor.<ref name="moungenot" /><ref>{{cite journal |last1=Mascle |first1=J |last2=Moungenot |first2=D. |last3=Blarez |first3=E. |last4=Marinho |first4=M. |last5=Virlogeux |first5=P. |title=African transform continental margins: examples from Guinea, the Ivory Coast and Mozambique |journal=Geological Journal |volume=22 |series=2 |pages=537–561 |doi=10.1002/gj.3350220632 |year=1987 |issue=S2 |bibcode=1987GeolJ..22S.537M }}</ref> Its movement is concurrent with the EAR.<ref>{{cite journal |last=Scrutton |first=R.A. |title=Davie fracture zone and the movement of Madagascar |journal=Earth and Planetary Science Letters |year=1978 |volume=39 |issue=1 |pages=84–88 |doi=10.1016/0012-821x(78)90143-7 |bibcode=1978E&PSL..39...84S}}</ref>
== Competing theories on geologic evolution == Over time, many theories have tried to clarify the evolution of the East African Rift. In 1972 it was proposed that the EAR was not caused by tectonic activity, but rather by differences in crustal density. Since the 1990s, evidence has been found in favor of mantle plumes beneath the EAR.<ref>{{Cite journal |last=Montelli |first=R.G. |display-authors=et al. |date=2006 |title=A catalogue of deep mantle plumes: New results from finite-frequency tomography |journal=Geochem. Geophys. Geosyst. |volume=7 |issue=11 |article-number=2006GC001248 |pages=n/a |doi=10.1029/2006GC001248 |doi-access= |bibcode=2006GGG.....711007M}}</ref> Others proposed an African [[superplume]] causing mantle deformation.<ref name="ebinger-sleep">{{cite journal |last1=Ebinger |first1=C. J. |author-link1=Cynthia Ebinger |last2=Sleep |first2=N. H. |title=Cenozoic magmatism throughout east Africa resulting from impact of a single plume |journal=Nature |date=October 1998 |volume=395 |issue=6704 |pages=788–791 |doi=10.1038/27417 |bibcode=1998Natur.395..788E |s2cid=4379613}}</ref><ref name="corti-esr">{{cite journal |last1=Corti |first1=Giacomo |title=Continental rift evolution: From rift initiation to incipient break-up in the Main Ethiopian Rift, East Africa |journal=Earth-Science Reviews |date=September 2009 |volume=96 |issue=1–2 |pages=1–53 |doi=10.1016/j.earscirev.2009.06.005 |bibcode=2009ESRv...96....1C}}</ref><ref>{{cite journal |last1=Hansen |first1=Samantha E. |last2=Nyblade |first2=Andrew A. |last3=Benoit |first3=Margaret H. |title=Mantle structure beneath Africa and Arabia from adaptively parameterized P wave tomography: Implications for the origin of Cenozoic Afro-Arabian tectonism |journal=Earth and Planetary Science Letters |date=February 2012 |volume=319-320 |pages=23–34 |doi=10.1016/j.epsl.2011.12.023 |bibcode=2012E&PSL.319...23H}}</ref> Although the effects of deep-rooted [[mantle plumes]] are an important hypothesis, their location and dynamics are poorly understood, and a matter of active research.<ref name="kearey" /> The question is still debated.
[[File:Emryetal2018 Africa Vs Depth Slices.pdf|thumb|Maps of four different depth slices of the Shear-velocity (Vs) model developed by Emry et al. 2018.<ref>{{cite journal |last1=Trabant |first1=C. |last2=Hutko |first2=A. R. |last3=Bahavar |first3=M. |last4=Karstens |first4=R. |last5=Ahern |first5=T. |last6=Aster |first6=R. |title=Data Products at the IRIS DMC: Stepping Stones for Research and Other Applications |journal=Seismological Research Letters |date=6 September 2012 |volume=83 |issue=5 |pages=846–854 |doi=10.1785/0220120032|bibcode=2012SeiRL..83..846T }}</ref> The forms of the zones with lower Vs (colors toward red) suggest the hotter structures in the Mantle. The distinguishing fourth map depicts a depth below the 410 km discontinuity where Vs steeps up (getting overall bluer), but it still displays the signature of a plume at the substrate of the East African Rift. In the white box, the Vs vertical profile at 10°N, 40°E illustrates the increase of velocity with depth and the effect of the 410 km discontinuity.]]
The most recent and accepted view is the theory put forth in 2009: that [[magmatism]] and [[plate tectonics]] have a feedback with one another, controlled by oblique rifting conditions. According to this theory, lithospheric thinning generates volcanic activity, further increasing magmatic processes such as [[intrusion]]s and numerous small plumes. These processes further thin the [[lithosphere]] in saturated areas, making the thinning lithosphere behave like a [[mid-ocean ridge]].<ref name="corti-esr" /> According to marine geologist [[Kathleen Crane]], the rift could eventually cause eastern Africa to separate from the mainland, although this potential event could take tens of millions of years.<ref>{{Cite book |last=Gray |first=William R. |url=https://archive.org/details/naturesworldofwo00fish/page/16/ |title=Nature's World of Wonders |publisher=[[National Geographic Society]] |year=1983 |isbn=978-2-09-290310-0 |location=Washington, D.C. |pages=16}}</ref>
Studies that contribute to the broader understanding on the evolution of rifts can be grouped into the techniques of isotope geochemistry, seismic tomography and geodynamical modeling.
=== Isotope geochemistry === The varying geochemical signatures of a suite of Ethiopian lavas suggest multiple plume sources: at least one of deep mantle origin, and one from within the subcontinental lithosphere.<ref>{{cite journal |last1=Furman |first1=Tanya |title=Geochemistry of East African Rift basalts: An overview |journal=Journal of African Earth Sciences |date=June 2007 |volume=48 |issue=2–3 |pages=147–160 |doi=10.1016/j.jafrearsci.2006.06.009 |bibcode=2007JAfES..48..147F}}</ref> In accordance, a 2014 study compares the geochemical signature of [[Rare-earth element|rare earth]] [[isotopes]] from [[xenolith]]s and lava samples collected in the EAR. The results corroborate the coexistence of a superplume "common to the entire rift" with another mantle material source being either of subcontinental type or of mid-ocean ridge type.<ref>{{cite journal |last1=Halldórsson |first1=Saemundur A. |last2=Hilton |first2=David R. |last3=Scarsi |first3=Paolo |last4=Abebe |first4=Tsegaye |last5=Hopp |first5=Jens |title=A common mantle plume source beneath the entire East African Rift System revealed by coupled helium-neon systematics |journal=Geophysical Research Letters |date=16 April 2014 |volume=41 |issue=7 |pages=2304–2311 |doi=10.1002/2014GL059424 |doi-access= |bibcode=2014GeoRL..41.2304H}}</ref>
=== Seismic tomography === The geophysical method of [[seismic tomography]] is a suitable tool to investigate Earth's subsurface structures deeper than the crust. It is an inverse problem technique that models which are the velocities of the inner Earth that reproduce the seismographic data recorded all around the world. Recent improvements of tomographic Earth models of [[P wave]] and [[S wave]] velocities suggest that a superplume upwelling from the lower mantle at the northeastern EAR feeds plumes of smaller scale into the [[upper mantle (Earth)|upper mantle]].<ref>{{cite journal |last1=Civiero |first1=Chiara |last2=Hammond |first2=James O. S. |last3=Goes |first3=Saskia |last4=Fishwick |first4=Stewart |last5=Ahmed |first5=Abdulhakim |last6=Ayele |first6=Atalay |last7=Doubre |first7=Cecile |last8=Goitom |first8=Berhe |last9=Keir |first9=Derek |last10=Kendall |first10=J.-Michael |last11=Leroy |first11=Sylvie |last12=Ogubazghi |first12=Ghebrebrhan |last13=Rümpker |first13=Georg |last14=Stuart |first14=Graham W. |title=Multiple mantle upwellings in the transition zone beneath the northern East-African Rift system from relative P wave travel-time tomography |journal=Geochemistry, Geophysics, Geosystems |date=September 2015 |volume=16 |issue=9 |pages=2949–2968 |doi=10.1002/2015GC005948 |doi-access=free |bibcode=2015GGG....16.2949C|hdl=2158/1077599 |hdl-access=free }}</ref><ref>{{cite journal |last1=Emry |first1=E. L. |last2=Shen |first2=Y. |last3=Nyblade |first3=A. A. |last4=Flinders |first4=A. |last5=Bao |first5=X. |title=Upper mantle earth structure in Africa from full-wave ambient noise tomography |journal=Geochemistry, Geophysics, Geosystems |volume=20 |pages=120–147 |doi=10.1029/2018GC007804 |doi-access=free |year=2019 |issue=1 |bibcode=2019GGG....20..120E}}</ref>
=== Geodynamical modeling === Parallel to geological and geophysical measures (e.g. isotope ratios and seismic velocities) it is constructive to test hypotheses on computer based geodynamical models. A 3D numerical geodynamic model of the plume-crust coupling was capable of reproducing the lateral asymmetry of the EAR around the [[Tanzania craton]].<ref>{{cite journal |last1=Koptev |first1=Alexander |last2=Burov |first2=Evgueni |last3=Calais |first3=Eric |last4=Leroy |first4=Sylvie |last5=Gerya |first5=Taras |last6=Guillou-Frottier |first6=Laurent |last7=Cloetingh |first7=Sierd |title=Contrasted continental rifting via plume-craton interaction: Applications to Central East African Rift |journal=Geoscience Frontiers |date=March 2016 |volume=7 |issue=2 |pages=221–236 |doi=10.1016/j.gsf.2015.11.002 |bibcode=2016GeoFr...7..221K |doi-access=free|hdl=20.500.11850/112690 |hdl-access=free }}</ref> Numerical modeling of plume-induced continental break-up shows two distinct stages, crustal rifting followed by lithospheric breakup, and the upwelling between stages of an upper mantle plume.<ref>{{cite journal |last1=Koptev |first1=Alexander |last2=Burov |first2=Evgueni |last3=Gerya |first3=Taras |last4=Le Pourhiet |first4=Laetitia |last5=Leroy |first5=Sylvie |last6=Calais |first6=Eric |last7=Jolivet |first7=Laurent |title=Plume-induced continental rifting and break-up in ultra-slow extension context: Insights from 3D numerical modeling |journal=Tectonophysics |date=October 2018 |volume=746 |pages=121–137 |doi=10.1016/j.tecto.2017.03.025 |bibcode=2018Tectp.746..121K |s2cid=132400572 |url=https://hal.sorbonne-universite.fr/hal-01500770/file/Koptev_Plume-induced.pdf}}</ref>
== Geologic evolution == Prior to the rift's formation, enormous [[Large igneous province|continental flood basalts]] erupted, uplifting the [[Ethiopian plateau|Ethiopian]], Somali, and East African plateaus. The first stage of rifting of the EAR was characterized by rift localization and magmatism along the entire rift zone. Periods of extension alternated with relative inactivity. There was also the reactivation of a pre-Cambrian weakness in the crust, a [[suture zone]] of multiple [[cratons]], displacement along large boundary faults, and the development of deep asymmetric basins.<ref name="corti-erv" /> The second stage of rifting was characterized by the deactivation of large boundary faults, the development of internal fault segments, and the concentration of magmatic activity towards the rifts.
Today, the narrow rift segments of the East African Rift system form zones of localized strain. These rifts are the result of the actions of numerous normal [[Fault (geology)|faults]] which are typical of all tectonic rift zones. As aforementioned, voluminous magmatism and continental flood basalts characterize some of the rift segments, while other segments, such as the Western branch, have only very small volumes of volcanic rock.<ref name="kearey" />
== Petrology == [[File:Albertine Rift, East African Rift (artificial rendering).jpg|thumb|upright=1.3|alt=An artificial computer rendering depicting the Albertine Rift|An artificial rendering of the [[Albertine Rift]], which forms the western branch of the East African Rift. Visible features include (from background to foreground): [[Lake Albert (Africa)|Lake Albert]], the [[Rwenzori Mountains]], [[Lake Edward]], the volcanic [[Virunga Mountains]], [[Lake Kivu]], and the northern part of [[Lake Tanganyika]]]] The African [[continental crust]] is generally cool and strong. Many [[craton]]s are found throughout the EAR, such as the [[Tanzania craton|Tanzania]] and [[Kaapvaal craton]]s. The cratons are thick, and have survived for billions of years with little tectonic activity. They are characterized by [[greenstone belts]], [[tonalite]]s, and other high-grade metamorphic lithologies. The cratons are of significant importance in terms of [[mineral resources]], with major deposits of [[gold]], [[antimony]], [[iron]], [[chromium]] and [[nickel]].<ref>{{cite web |last1=Taylor |first1=C.D. |title=Geology and Nonfuel Mineral Deposits of Africa and Middle East |publisher=US Department of the Interior, US Geological Survey |last2=Schulz |first2=K.J. |last3=Doebrich |first3=J.L. |last4=Orris |first4=G.J. |last5=Denning |first5=P.D. |last6=Kirschbaum |first6=M.J. |url=https://pubs.usgs.gov/of/2005/1294/e/}}</ref>
A large volume of continental flood basalts erupted during the [[Oligocene]], with the majority of the volcanism coinciding with the opening of the Red Sea and the Gulf of Aden approximately 30 Ma.<ref name="ebinger-sleep" /><ref name="kearey">{{cite book |last1=Kearey |first1=Philip |title=Global Tectonics |url={{Google books|HPuEDwAAQBAJ |plainurl=yes}} |year=2009 |publisher=John Wiley & Sons |last2=Klepeis |first2=Keith A. |last3=Vine |first3=F.J. |isbn=978-1-4051-0777-8}}{{page needed|date=March 2019}}</ref> The composition of the volcanics are a continuum of ultra-alkaline to tholeiitic and felsic rocks. It has been suggested that the diversity of the compositions could be partially explained by different mantle source regions. The EAR also cuts through old sedimentary rocks deposited in ancient basins.<ref name="saemundsson">{{cite journal |last=Saemundsson |first=K |title=East African Rift System-An Overview |journal=Reykjavik: United Nations University, Iceland GeoSurvey |year=2009}}</ref>
== Volcanism and seismicity == The East African Rift Zone includes a number of active and dormant volcanoes, among them: [[Mount Kilimanjaro]], [[Mount Kenya]], [[Mount Longonot]], [[Menengai]] Crater, [[Mount Karisimbi]], [[Mount Nyiragongo]], [[Mount Meru (Tanzania)|Mount Meru]] and [[Mount Elgon]], as well as the [[Crater Highlands]] in Tanzania. Although most of these mountains lie outside of the rift valley, the EAR created them.<ref name="saemundsson" />
Notable active examples of EAR volcanism include [[Erta Ale]], [[Dalaffilla]] (also called Gabuli, Alu-Dalafilla), [[Hayli Gubbi]] (which erupted in 2025), and [[Ol Doinyo Lengai]]. Erta Ale is a basaltic shield volcano in the Afar Region of northeastern Ethiopia, active continuously since at least 1967,<ref>{{cite journal |last1=Oppenheimer |first1=C. |last2=Francis |first2=P. |title=Remote sensing of heat, lava and fumarole emissions from Erta 'Ale volcano, Ethiopia |journal=Int. J. Remote Sens. |volume=18 |pages=1661–1692 |date=1996 |issue=8 |url=https://www.researchgate.net/publication/233215020|doi=10.1080/014311697218043}}</ref> with a summit lava lake documented since at least 1906.<ref>{{cite journal |last1=Dainelli |first1=G. |last2=Marinelli |first2=O. |title=Dell'Erta-ale, vulcano ritenuto attivo della Dancalia settentrionale |journal=Rivista Geografica Italiana |volume=13 |pages=261–270 |date=1906}}</ref> The 2008 eruption of Dalafilla, its only documented activity since the start of the [[Holocene]],<ref>{{cite gvp |name=Alu-Dalafilla |vn=221060 |access-date=15 July 2021}}</ref> is the largest recorded eruption in Ethiopian history.{{Citation needed|date=February 2021}} Ol Doinyo Lengai is currently the only active [[natrocarbonatite]] volcano on Earth.<ref name=gvp>{{cite gvp |name=Ol Doinyo Lengai |vn=222120 |access-date=15 July 2021}}</ref> Its magma contains almost no silica; typical lava flows have [[viscosity|viscosities]] of less than 100 Pa⋅s,<ref>{{cite journal |last1=Kervyn |first1=Matthieu |last2=Ernst |first2=Gerald G. J. |last3=Klaudius |first3=Jurgis |last4=Keller |first4=Jörg |last5=Kervyn |first5=François |last6=Mattson |first6=Hannes B. |last7=Belton |first7=Frederic |last8=Mbede |first8=Evelyne |last9=Jacobs |first9=Patric |title=Voluminous lava flows at Oldoinyo Lengai in 2006: chronology of events and insights into the shallow magmatic system |journal=Bull Volcanol |volume=70 |pages=1069–1086 |date=2008 |issue=9 |doi=10.1007/s00445-007-0190-x |bibcode=2008BVol...70.1069K |s2cid=46977110 |url=https://biblio.ugent.be/publication/430096/file/448941 |hdl=1854/LU-430096 |hdl-access=free}}</ref> comparable to olive oil at {{cvt|26|C|F}}. EAR-related volcanic structures with dated activity since the onset of the Holocene include approximately 50 in Ethiopia,<ref name="corti-erv" /> [[List of volcanoes in Kenya|17 in Kenya]], and [[List of volcanoes in Tanzania|9 in Tanzania]].
The EAR is the largest seismically active rift system on Earth today. The majority of [[earthquakes]] occur near the Afar Depression, with the largest typically occurring along or near major border faults.<ref name="kearey" /> Seismic events in the past century are estimated to have reached a maximum moment magnitude of 7.0.{{Citation needed|date=February 2021}} The seismicity trends parallel to the rift system, with a shallow focal depth of {{Convert|12–15|km||abbr=on}} beneath the rift axis. Further away from the rift axis, focal depths can be below {{Convert|30|km||abbr=on}}.<ref name="kearey" /><ref>{{cite book |last1=Siebert |first1=L. |title=Volcanoes of the World |year=2010 |publisher=University of California Press |last2=Simkin |first2=T. |last3=Kimberly |first3=P.}}</ref> [[Focal mechanism]] solutions strike NE and frequently demonstrate normal dip-slip faulting, although left-lateral motion is also observed.<ref name="corti-erv" />
==Effect on climate ==
The East African Rift system affects regional, continental and even global climate. Regions of higher elevation, including the [[Ethiopian Highlands]] and the Kenya Highlands are hotspots of higher rainfall amid the semi-arid to arid lowlands of East Africa.<ref>{{Cite journal |doi=10.1175/JCLI-D-19-0274.1 |title=Deep Convection over Africa: Annual Cycle, ENSO, and Trends in the Hotspots |date=2019 |last1=Washington |first1=Richard |last2=Hart |first2=Neil C. G. |last3=Maidment |first3=Ross I. |journal=Journal of Climate |volume=32 |issue=24 |pages=8791–8811 |bibcode=2019JCli...32.8791H |doi-access=free |url=https://ora.ox.ac.uk/objects/uuid:0cfb07b3-338a-40b1-ae12-23aebd46275c/files/rw0892b02n }}</ref> Lakes which form within the rift, including [[Lake Victoria]], have a large effect on regional climate.<ref>{{Cite journal |doi=10.1002/2016RG000544 |title=Climate and climatic variability of rainfall over eastern Africa |date=2017 |last1=Nicholson |first1=Sharon E. |journal=Reviews of Geophysics |volume=55 |issue=3 |pages=590–635 |bibcode=2017RvGeo..55..590N |s2cid=133035406 |doi-access=free }}</ref> They are a source of water vapour, and also lead to the formation of [[sea breeze|lake breeze systems]], which affect weather across large areas of East Africa. The east to west river valleys within the rift system, including the Turkana Channel in northern [[Kenya]] and the [[Zambezi]] river valley, concentrate low-level easterly winds and accelerate them towards [[Central Africa]].<ref>{{Cite journal |doi=10.1029/2020GL090999 |title=African Low-Level Jets and Their Importance for Water Vapor Transport and Rainfall |date=2021 |last1=Munday |first1=Callum |last2=Washington |first2=Richard |last3=Hart |first3=Neil |journal=Geophysical Research Letters |volume=48 |issue=1 |article-number=e2020GL090999 |bibcode=2021GeoRL..4890999M |s2cid=230529018 |doi-access=free |url=https://ora.ox.ac.uk/objects/uuid:4fbaba19-3d02-4392-a6cd-9815021a50aa/files/rbr86b458r }}</ref> This leaves East Africa drier than it otherwise would be, and also supports the high rainfall in the [[Congo Basin]] [[rainforest]].<ref name="ReferenceA">{{Cite journal |doi=10.1038/s41586-022-05662-5 |title=Valley formation aridifies East Africa and elevates Congo Basin rainfall |date=2023 |last1=Munday |first1=Callum |last2=Savage |first2=Nicholas |last3=Jones |first3=Richard G. |last4=Washington |first4=Richard |journal=Nature |volume=615 |issue=7951 |pages=276–279 |pmid=36859546 |bibcode=2023Natur.615..276M |s2cid=257282295 }}</ref> The formation of the east–west valleys could in turn be important for the [[aridification]] of East Africa over millions of years.<ref name="ReferenceA"/>
The barrier presented by EARS concentrates monsoonal winds (known as the Somali Jet) in the western [[Indian Ocean]].<ref>{{Cite journal |pmid=15598618 |date=2005 |last1=Slingo |first1=J. |last2=Spencer |first2=H. |last3=Hoskins |first3=B. |last4=Berrisford |first4=P. |last5=Black |first5=E. |title=The meteorology of the Western Indian Ocean, and the influence of the East African Highlands |journal=Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences |volume=363 |issue=1826 |pages=25–42 |doi=10.1098/rsta.2004.1473 |s2cid=2953876 }}</ref> The Somali Jet supplies water vapour for the high rainfall during the [[Monsoon of South Asia|Indian Monsoon]]<ref>{{Cite journal |doi=10.1002/qj.388 |title=Annual intensification of the Somali jet in a quasi-equilibrium framework: Observational composites |date=2009 |last1=Boos |first1=William R. |last2=Emanuel |first2=Kerry A. |journal=Quarterly Journal of the Royal Meteorological Society |volume=135 |issue=639 |pages=319–335 |bibcode=2009QJRMS.135..319B |s2cid=40870356 |doi-access=free |hdl=1721.1/64676 |hdl-access=free }}</ref> and is responsible for roughly half the global cross-equatorial atmospheric mass flux in the lower-branch of [[Hadley Circulation]].<ref>{{Cite journal |doi=10.1002/qj.49709540412 |title=Interhemispheric transport of air in the lower troposphere over the western Indian Ocean |date=1969 |last1=Findlater |first1=J. |journal=Quarterly Journal of the Royal Meteorological Society |volume=95 |issue=404 |pages=400–403 |bibcode=1969QJRMS..95..400F }}</ref>
== Discoveries in human evolution == {{Main|Human evolution|Timeline of human evolution}} The Rift Valley in East Africa has been a rich source of [[hominid]] fossils that allow the study of human evolution.<ref name="corti-erv" /><ref>{{cite web |title=Great Rift Valley Ecosystem – UNESCO World Heritage Centre |url=http://whc.unesco.org |publisher=UNESCO |access-date=14 March 2008}}</ref> The rapidly eroding highlands quickly filled the valley with sediments, creating a favorable environment for the preservation of remains. The bones of several hominid ancestors of modern humans have been found here, including those of "[[Lucy (hominid)|Lucy]]", a partial [[australopithecine]] skeleton discovered by anthropologist [[Donald Johanson]] dating back over 3 million years. [[Richard Leakey|Richard]] and [[Mary Leakey]] have also done significant work in this region.<ref>{{cite journal |last=Gibbons |first=A. |title=Profile: Michel Brunet: One Scientist's Quest for the Origin of Our Species |journal=Science |year=2002 |volume=298 |issue=5599 |pages=1708–1711 |doi=10.1126/science.298.5599.1708 |pmid=12459568 |s2cid=26316640}}</ref> In 2008, two other hominid ancestors were discovered here: a 10-million-year-old ape called ''[[Chororapithecus abyssinicus]]'', found in the Afar rift in eastern Ethiopia, and ''[[Nakalipithecus nakayamai]]'', which is also 10 million years old.<ref>{{cite news |last=Seward |first=Liz |title=Fossils belong to new great ape |access-date=14 March 2008 |publisher=BBC News London |year=2007 |url=https://news.bbc.co.uk/2/hi/6958313.stm}}</ref>
== See also == *[[Baikal Rift Zone]] *[[Lake Victoria]] *[[Northern Cordilleran Volcanic Province]] *[[West Antarctic Rift System]] *[[West and Central African Rift System]]
== References == {{Reflist}}
{{Major African geological formations}} {{Regions of Africa}} {{Authority control}}
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[[Category:Cenozoic rifts and grabens]] [[Category:Great Rift Valley]]