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East African Rift
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, in which 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 annually. As extension continues, lithospheric rupture will occur within 10 million years, the Somalian plate will break off, and a new ocean basin will form.
==Extent==
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. The Western 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 in the Afar Depression of Ethiopia through eastern Africa, terminating in Mozambique. The EAR transects through Ethiopia, Kenya, Uganda, Rwanda, Burundi, Zambia, Tanzania, 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 2200 km-long 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 wide, with a west facing scarp (east-plunging arch) along the southern half of its length that rises up to 2300 m above the sea floor.〔 Its movement is concurrent with the EAR.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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