The East African
Rift (EAR) is an active continental rift zone in East
Africa. The EAR began developing around the onset of the Miocene,
22–25 million years ago. In the past, it was considered to be
part of a larger Great
Rift Valley that extended north to Asia Minor.
The rift is a narrow zone that is a developing divergent tectonic
plate 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 6–7 mm (0.24–0.28 in) annually.
As extension continues, lithospheric rupture will occur within 10
million years, the Somali plate will break off, and a new ocean basin
2 Competing theories on geologic evolution
3 Geologic evolution
5 Volcanism and seismicity
6 Discoveries in human evolution
7 See also
A series of distinct rift basins, the East African
Rift System extends
over thousands of kilometers. The EAR consists of two main
branches. The Eastern
Rift Valley (also known as Gregory Rift)
includes the Main Ethiopian Rift, running eastward from the Afar
Triple Junction, which continues south as the Kenyan
Rift Valley includes the Albertine Rift, and farther
south, the valley of Lake Malawi. To the north of the Afar Triple
Junction, the rift follows one of two paths: west to the Red Sea Rift
or east to the
Aden Ridge in the Gulf of Aden.
The EAR runs from the
Afar Triple Junction
Afar Triple Junction in the
Afar Triangle of
Ethiopia through eastern Africa, terminating in Mozambique. The EAR
transects through Ethiopia, Kenya, Uganda, Rwanda, Burundi, Zambia,
Malawi and Mozambique. It also runs offshore of the coast of
Mozambique along the Kerimba and Lacerda grabens, which are joined by
the Davie Ridge, a 2,200 km-long (1,400 mi) relic fracture
zone that cuts across the West Somali basin, straddling the boundary
Tanzania and Mozambique. The Davie Ridge ranges between
30–120 km (19–75 mi) wide, with a west facing scarp
(east-plunging arch) along the southern half of its length that rises
up to 2,300 m (7,500 ft) above the sea floor. Its
movement is concurrent with the EAR.
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.
Others proposed an African superplume causing mantle
deformation. However, 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. Additionally, the subject of deep-rooted mantle plumes is
still a matter of controversy, and therefore cannot be confirmed.
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. At that time it was
suggested that lithospheric thinning generated volcanic activity,
further increasing the magmatic processes at play such as intrusions
and numerous small plumes. These processes further thin the
lithosphere in saturated areas, forcing the thinning lithosphere to
behave like a mid-ocean ridge.
Prior to rifting, enormous continental flood basalts erupted on the
surface and uplift of the Ethiopian, Somali, and East African plateaus
occurred. The first stage of rifting of the EAR is characterized by
rift localization and magmatism along the entire rift zone. Periods of
extension alternated with times of 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. The second stage of
rifting is 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 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
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, 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
cratons are found throughout the EAR, such as the
Kaapvaal cratons. The cratons are thick, and have survived for
billions of years with little tectonic activity. They are
characterized by greenstone belts, tonalites, 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.
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
Gulf of Aden approximately 30
Ma. 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.
Volcanism and seismicity
The East African
Rift Zone includes a number of active as well as
dormant volcanoes, among them: Mount Kilimanjaro, Mount Kenya, Mount
Menengai Crater, Mount Karisimbi, Mount Nyiragongo, 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.
Active volcanos include Erta Ale, DallaFilla, and Ol Doinyo Lengai,
the former of which is a continuously active basaltic shield volcano
in the Afar Region of northeastern Ethiopia. When DallaFilla erupted
in 2008 it was the largest volcanic eruption in
Ethiopia in recorded
Ol Doinyo Lengai
Ol Doinyo Lengai volcano is currently the only active
natrocarbonatite volcano in the world. The magma contains almost no
silica, making the flow viscosity extremely low. “Its lava fountains
crystallize in midair then shatter like glass” according to the
National Geographic. Approximately 50 volcanic structures in Ethiopia
alone have documented activity since the onset of the Holocene.
The EAR is the largest seismically active rift system on Earth today.
The majority of earthquakes occur near the Afar Depression, with the
largest earthquakes typically occurring along or near major border
faults. Seismic events in the past century are estimated to have
reached a maximum moment magnitude of 7.0. The seismicity trends
parallel to the rift system, with a shallow focal depth of
12–15 km (7.5–9.3 mi) beneath the rift axis. Further
away from the rift axis, focal depths can reach depths of over
30 km (19 mi).
Focal mechanism solutions strike NE
and frequently demonstrate normal dip-slip faults, although
left-lateral motion is also observed.
Discoveries in human evolution
Human evolution and Timeline of human evolution
Rift Valley in
East Africa has been a rich source of hominid
fossils that allow the study of human evolution. 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", a partial australopithecine skeleton
discovered by anthropologist
Donald Johanson dating back over 3
million years. Richard and
Mary Leakey have done significant work in
this region also. More recently, two other hominid ancestors have
been 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.
Northern Cordilleran Volcanic Province
West Antarctic Rift
West and Central African
^ Ebinger, C.J. (2005). "Continental break-up: the East African
perspective". Astron. Geophys. 46: 216–21.
^ Fernandes, R.M.S.; Ambrosius, B.A.C.; Noomen, R.; Bastos, L.;
Combrinck, L.; Miranda, J.M.; Spakman, W. (2004). "Angular velocities
Nubia and Somalia from continuous GPS data: implications on
present-day relative kinematics". Earth Planet. Sci. Lett. 222:
^ a b c d e Corti, G. "The Ethiopian
Rift Valley". National Research
Council of Italy, Institute of Geosciences and Earth Resources.
Retrieved March 19, 2014.
^ a b c Moungenot, D.; Recq, M.; Virlogeux, P.; Lepvrier, C. (1986).
"Seaward extension of the East African Rift". Letters to Nature. 321
(6070): 599. Bibcode:1986Natur.321..599M. doi:10.1038/321599a0.
^ Chorowicz, Jean (2005). "The East African rift system". Journal of
African Earth Sciences. 43 (1): 379–410.
^ Mascle, J; Moungenot, D.; Blarez, E.; Marinho, M.; Virlogeux, P.
(1987). "African transform continental margins: examples from Guinea,
Ivory Coast and Mozambique". Geological journal. 2. 22: 537–561.
^ Scrutton, R.A. (1978). "David fracture zone and the movement of
Madagascar". Earth and Planetary Science Letters. 39 (1): 84–88.
^ Logatchev, N.A.; Beloussov, V.V.; Milanovsky, E.E. (1972). "East
African rift development". Tectonophysics. 15 (1): 71–81.
^ a b Ebinger, C.J.; Sleep, N.H. (1998). "Cenozoic magmatism
Africa resulting from impact of a single plume".
Nature. 395 (6704): 788–791. Bibcode:1998Natur.395..788E.
^ a b Corti, G (2009). "Continental rift evolution: from rift
initiation to incipient break-up in the Main Ethiopian Rift, East
Africa". Earth-Science Reviews. 96 (1): 1–53.
^ a b c d e Kearey, P; Klepeis, K.A.; Vine, F.J. (2009). Global
Tectonics. John Wiley & Sons.
^ Taylor, C.D.; Schulz, K.J.; Doebrich, J.L.; Orris, G.J.; Denning,
P.D.; Kirschbaum, M.J. "Geology and Nonfuel Mineral Deposits of Africa
and Middle East". US Department of the Interior, US Geological
^ a b Saemundsson, K (2009). "East African
Rift System-An Overview".
Reykjavik: United Nations University, Iceland GeoSurvey.
^ Siebert, L.; Simkin, T.; Kimberly, P. (2010). Volcanoes of the
World. University of California Press.
Rift Valley Ecosystem – UNESCO World Heritage Centre".
UNESCO. Retrieved March 14, 2008.
^ Gibbons, A. (2002). "Profile: Michel Brunet: One Scientist's Quest
for the Origin of Our Species". Science. 298 (5599): 1708–1711.
doi:10.1126/science.298.5599.1708. PMID 12459568.
^ Seward, Liz (2007). "Fossils belong to new great ape". BBC News
London. Retrieved March 14, 2008.
Major African geological formations
Cratons and shields
West African Craton
Broodkop Shear Zone
Central African Shear Zone
Chuan Shear Zones
Foumban Shear Zone
Kandi Fault Zone
Mwembeshi Shear Zone
Todi Shear Zone
Western Meseta Shear Zone
Cape Fold Belt
East African Orogen
Terra Australis Orogen
Bahr el Arab rift
Blue Nile rift
East African Rift
Gulf of Suez Rift
Red Sea Rift
White Nile rift
Blue Nile Basin
Foreland Karoo Basin
Niger Delta Basin
Orange River basin
Ouled Abdoun Basin
Rio del Rey Basin
Somali Coastal Basin
Tanzania Coastal Basin
Central Pangean Mountains
East African mountains
Great Karas Mountains
Serra da Leba
Serra da Chela
Regions of Africa
Gulf of Guinea
African Great Lakes
East African Rift
Rift Valley lakes
Horn of Africa
Gulf of Aden
Gulf of Tadjoura
Indian Ocean islands
Cataracts of the Nile
Gulf of Aqaba
Gulf of Guinea
Guinean Forests of West Africa
Inner Niger Delta
Central Highlands (Madagascar)
Cape Floristic Region
East African montane forests
Greater Middle East
Islands of Africa
List of countries where Arabic is an official language
Portuguese-speaking African countries
Coordinates: 3°00′00″S 35°30′00″E / 3.0000°S