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43-495: The plateau extends northwest-southeast, rising between two segments of the East African Rift . Lake Tanganyika (lake surface 773 m elevation) lies to the southwest in the western branch of the rift, and the graben valley of Lake Rukwa (lake surface 793 meters elevation) lies to the northeast. The plateau rises in steep escarpments above both lake valleys, and includes extensive areas above 2000 meters elevation. Mbizi (2490 m)

86-516: 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. 3°00′S 35°30′E  /  3.0°S 35.5°E  / -3.0; 35.5 Gregory Rift The Gregory Rift ( Ufa la Gregori , in Swahili ) is the eastern branch of the East African Rift fracture system. The rift

129-513: A great fault. Thomson returned in 1883, traveling through the rift valley in Kenya from Mount Longonot to Lake Baringo . Describing the valley around this lake he said: "Imagine if you can a trough or depression 3300 feet above sea level, and twenty miles broad, the mountains rising with very great abruptness on both sides to a height of 9000 feet". John Walter Gregory visited central Kenya in 1893 and again in 1919. His 1896 book The Great Rift Valley

172-633: A number of active and dormant volcanoes, among them: Mount Kilimanjaro , Mount Kenya , Mount Longonot , 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. Notable active examples of EAR volcanism include Erta Ale , Dalaffilla (also called Gabuli, Alu-Dalafilla), and Ol Doinyo Lengai . Erta Ale

215-779: Is a basaltic shield volcano in the Afar Region of northeastern Ethiopia, active continuously since at least 1967, with a summit lava lake documented since at least 1906. The 2008 eruption of Dalafilla, its only documented activity since the start of the Holocene , is the largest recorded eruption in Ethiopian history. Ol Doinyo Lengai is currently the only active natrocarbonatite volcano on Earth. Its magma contains almost no silica; typical lava flows have viscosities of less than 100 Pa⋅s, comparable to olive oil at 26 °C (79 °F). EAR-related volcanic structures with dated activity since

258-570: Is an active continental rift zone in East Africa . The EAR began developing around the onset of the Miocene , 22–25 million years ago. It was formerly considered to be part of a larger Great Rift Valley that extended north to Asia Minor . A narrow zone, the rift is a developing divergent tectonic plate boundary where the African plate is in the process of splitting into two tectonic plates, called

301-661: Is being caused by the separation of the Somali Plate from the Nubian Plate , driven by a thermal plume . Although the term is sometimes used in the narrow sense of the Kenyan Rift , the larger definition of the Gregory Rift is the set of faults and grabens extending southward from the Gulf of Aden through Ethiopia and Kenya into Northern Tanzania , passing over the local uplifts of

344-633: Is considered a classic. Gregory was the first well-known European to use the term "rift valley", which he defined as "a linear valley with parallel and almost vertical sides, which has fallen owing to a series of parallel faults". In 1913 the German geologist Hans Reck made the first European study of the strata in the Olduvai Gorge to the west of the Crater Highlands. He brought a large collection of mammalian fossils back to Berlin. In 1928 Louis Leakey ,

387-479: 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 . 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. Prior to

430-665: Is crossed by two major roads. Tanzania's M8 highway extends from Mpanda to Sumbawanga, and then south to Mbala in Zambia. Sections of the M8 are unpaved. The Tunduma-Sumbawanga Road extends southeast from Sumbawanga to Tunduma on the Zambian border, where it meets the A104 highway and the TAZARA Railway . East African Rift The East African Rift ( EAR ) or East African Rift System ( EARS )

473-540: Is the highest peak, northeast of Sumbwawanga the edge of the escarpment overlooking Lake Rukwa. Malonje (2418 m) lies south of Mbizi. Most of the plateau lies in the closed drainage basin of Lake Rukwa. The southeastern portion of the plateau is drained by the Momba River and its tributaries, and the northeastern portion is drained by tributaries of the Rungwa River ; both rivers empty into Lake Rukwa. The western edge of

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516-542: The Ethiopian Highlands and the Kenya Highlands are hotspots of higher rainfall amid the semi-arid to arid lowlands of East Africa. Lakes which form within the rift, including Lake Victoria , have a large effect on regional climate. They are a source of water vapour, and also lead to the formation of lake breeze systems , which affect weather across large areas of East Africa. The east to west river valleys within

559-579: The Main Ethiopian Rift , runs southward from the Afar triple junction, and continues south as the Kenyan Rift Valley, then transects Congo DR , Uganda , Rwanda , Burundi , Zambia , Tanzania , Malawi and Mozambique . The Western Rift Valley includes the Albertine Rift , and farther south, the valley of Lake Malawi . The rift also continues offshore from the coast of Mozambique along

602-627: The Oligocene , with the majority of the volcanism coinciding with the opening of the Red Sea and the 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. The East African Rift Zone includes

645-674: The Somali plate and the Nubian plate , at a rate of 6–7 mm (0.24–0.28 in) per year. The rift system consists of three microplates, the Victoria microplate to the north, and the Rovuma and 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

688-399: The lithosphere in saturated areas, making the thinning lithosphere behave like a mid-ocean ridge . 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. Studies that contribute to the broader understanding on the evolution of rifts can be grouped into

731-560: The 1,300 kilometres (810 mi) wide East African Plateau . Large shield volcanoes near the margins of the craton and in the adjacent Mozambique belt issued large volumes of basaltic to trachytic magmatism between five and one million years ago, with faulting around 1.2 million years ago. Volcanic activity started in the central Ethiopian plateau around 30 million years ago, long before rifting began. The first period of activity deposited flood basalts and rhyolites from 500 metres (1,600 ft) to 2,000 metres (6,600 ft) thick. Uplift of

774-528: The Baringo – Bogoria half-graben from 500 metres (1,600 ft) to 1,000 metres (3,300 ft) thick and in the Afar depression up to 100 metres (330 ft) thick. The first well-known European geologist to explore the region was Joseph Thomson , a member of an expedition in 1879–1880 sponsored by the Royal Geographical Society of Britain. From his observations he deduced the existence of

817-404: 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. 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

860-850: The EARS. Many of the African Great Lakes lie within the Rift Valley. A series of distinct rift basins, the East African Rift System extends over thousands of kilometers. 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

903-523: The Ethiopian and Kenyan domes. Ancient fossils of early hominins , the ancestors of humans, have been found in the southern part of the Gregory Rift. The Gregory Rift is named in honour of the British geologist John Walter Gregory who explored the geology of the rift in 1892–93 and 1919. The Gregory Rift lies within the Mozambique belt , often considered to be the remains of an orogenic system similar to

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946-457: The Ethiopian plateau began around this time or soon after. Between 30 million and 10 million years ago synrift shield volcanoes deposited from 1,000 metres (3,300 ft) to 2,000 metres (6,600 ft) of additional material over the Ethiopian flood basalts. Rifting in Ethiopia began about 18 million years ago in the southwest and 11 million years ago in northern parts of the Main Ethiopian Rift as

989-579: The Himalayas. This belt runs from Ethiopia through Kenya, Tanzania and Mozambique . The rift is widest at the northern end in the Afar region, narrowing to a few kilometers in northern Tanzania, then splaying out in the North Tanzania Divergence. The Gregory Rift has shoulders rising over 3,000 metres (9,800 ft) above sea level, 1,000 metres (3,300 ft) above the inner part of the graben. The Tanzanian portion includes Mount Kilimanjaro ,

1032-585: 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 between 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 to 2,300 m (7,500 ft) above

1075-610: The Lyambo Hill Forest Reserve (212.39 km²) protect an enclave of montane rainforest on the slopes of Mount Mbizi, and montane grasslands at the summit. The Mbizi forest supports a population of Ugandan red colobus monkeys (Procolobus tephrosceles) . There are a chain of protected areas along the western escarpment, including Kalambo Falls Forest Reserve (5.63 km²), Kalambo River Forest Reserve (461.63 km²), Loasi River Forest Reserve (354.81 km²), and Lwafi-Nkamba Game Reserve (3388.57 km²). The plateau

1118-595: The Somali Jet) in the western Indian Ocean . The Somali Jet supplies water vapour for the high rainfall during the Indian Monsoon and is responsible for roughly half the global cross-equatorial atmospheric mass flux in the lower-branch of Hadley Circulation . The 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

1161-410: The anthropologist, visited Berlin, where he saw that some of Reck's materials were artifacts . Leakey began exploring Olduvai in the 1930s and collecting material that has led to the site being recognized as an important center of early hominin occupation. Volcanism and rifting started in Kenya in the northern region of Turkana between 40 and 35 million years ago and then spread north and south. To

1204-606: The development of deep asymmetric basins. 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 faults which are typical of all tectonic rift zones. As aforementioned, voluminous magmatism and continental flood basalts characterize some of

1247-563: The effects of deep-rooted mantle plumes are an important hypothesis, their location and dynamics are poorly understood, and a matter of active research. The question is still debated. 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 intrusions and numerous small plumes. These processes further thin

1290-537: The highest mountain in Africa, and the huge caldera of Ngorongoro In the Crater highlands This portion also contains Ol Doinyo Lengai , the world's only active carbonatite volcano. Lakes in the rift other than Lake Turkana are mostly small and shallow, some with fresh water but many being saline. The thickness of lake sediments is mostly unknown. In Lake Turkana they seem to be at most 4 kilometres (2.5 mi) thick, in

1333-405: 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 . Parallel to geological and geophysical measures (e.g. isotope ratios and seismic velocities) it

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1376-551: The onset of the Holocene include approximately 50 in Ethiopia, 17 in Kenya , and 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. Seismic events in the past century are estimated to have reached a maximum moment magnitude of 7.0. The seismicity trends parallel to

1419-606: The opening of the Gregory rift caused the Afar Triple Junction to form. Volcanism from the Middle Pleistocene onward formed a chain of volcanoes along the floor of the rift throughout its length, dividing it into separate valleys. There are some indications that the lithosphere may have thinned below the Gregory rift, although based on basalt geochemistry the lithosphere is at least 75 kilometres (47 mi) thick below

1462-510: The plateau drains into Lake Tangankyika. The Kalambo River drains the central plateau, and forms Kalambo Falls as it descends the escarpment towards Lake Tanganyika. The plateau has some wetland areas, including the Kale Swamp. Cities on the plateau include Sumbawanga , near the center of the plateau, and Namanyere in the northwest. The natural vegetation on most of the plateau is miombo woodland . The Mbizi Forest Reserve (17,373 ha) and

1505-724: The rift segments, while other segments, such as the Western branch, have only very small volumes of volcanic rock. The African continental crust is generally cool and strong. Many cratons are found throughout the EAR, such as the Tanzania and 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

1548-673: 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 . This leaves East Africa drier than it otherwise would be, and also supports the high rainfall in the Congo Basin rainforest . The formation of the east–west valleys could in turn be important for the aridification of East Africa over millions of years. The barrier presented by EARS concentrates monsoonal winds (known as

1591-451: 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 be below 30 km (19 mi). Focal mechanism solutions strike NE and frequently demonstrate normal dip-slip faulting, although left-lateral motion is also observed. The East African Rift system affects regional, continental and even global climate. Regions of higher elevation, including

1634-515: The rift's formation, enormous continental flood basalts erupted, uplifting the 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

1677-432: The sea floor. Its movement is concurrent with the EAR. 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. Others proposed an African superplume causing mantle deformation. Although

1720-453: The south of Kenya. The Gregory rift is oriented NS, and in the past the minimum horizontal tectonic stress direction was EW, the direction of extension. The alignment of rows of small vents , cones , domes and collapse pits in the Suswa , Silali and Kinangop Plateau regions support this theory. However, data from oil and gas exploration wells in Kenya, vents in volcanic shields to the east of

1763-484: The south volcanism and rifting happened together, first in other parts of northern Kenya around 30 million years ago, then around 15 million years ago in the central part of the Kenyan Rift , 12 million years ago in southern Kenya and 8 million years ago in northern Tanzania. When rifting reached the Tanzanian Craton , the rift split into the eastern Gregory Rift and the western Albertine Rift , which are separated by

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1806-410: The techniques of isotope geochemistry, seismic tomography and geodynamical modeling. 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. In accordance, a 2014 study compares the geochemical signature of rare earth isotopes from xenoliths and lava samples collected in

1849-455: 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 also done significant work in this region. In 2008, two other hominid ancestors were discovered here:

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