a system of major faults and grabens (rifts) that have developed against a background of recent uplifts in east Africa. The valley stretches meridionally from the northern edge of the Red Sea to the lower course of the Zambezi River. It also includes the graben of the Red Sea and its spurs (the Gulfs of Suez and Aqaba), as well as the graben of the Gulf of Aden. To the north of the Gulf of Aqaba, the Rift Valley continues across the Dead Sea and the Jordan River valley to the foothills of the Taurus Mountains, paralleling the Mediterranean coast of the Arabian peninsula.
Within Africa, the valley consists of two branches. The Afar graben in Ethiopia and, further, the graben belt running to the east of Lake Victoria, past the Elgon, Kenya, and Kilimanjaro volcanoes, and from the basin of Lake Rudolf to Lake Nyasa, are a continuation of the graben of the Red Sea. Roughly parallel to this eastern rift is the western rift, which skirts the eastern shore of Lake Victoria across Lakes Albert, Edward, Kivu, Tanganyika, and Rukwa to the northern end of Lake Nyasa. To the south of Lake Nyasa, the Rift Valley follows the graben of the Shire River valley to the Zambezi River.
The Great Rift Valley in its present form began to develop in the Oligocene period simultaneously with the formation of the major uplifts and orogeny in the eastern part of Africa and Arabia. Here the recent faults have in part used the strikes of the more ancient faults, which date back as far as the Precambrian period. The movements along the faults led to a great outburst of volcanic activity, which reached a peak in the Neocene period and has continued until the modern era. All the active volcanoes in Africa (with the exception of Mount Cameroun) are located in this zone. The seismicity of the valley is evidence of the recent movements along the faults. The Great Rift Valley is part of the world rift system and shows a great similarity with oceanic rifts.
In the opinion of some geologists, the general cause of the development of the rifts, volcanic activity, and seismicity in the Rift Valley is the breakup of the subcrusted matter of the upper mantle as a consequence of the heat flow from deeper parts of the earth’s interior. Others view these phenomena as related to the extension of the earth’s crust.