EAST AFRICAN RIFT SYSTEM

also called Afro-Arabian Rift Valley one of the most extensive rifts on the Earth's surface, extending from Jordan in southwestern Asia southward through eastern Africa to Mozambique. The system is some 4,000 miles (6,400 km) long and averages 3040 miles (4864 km) wide. The system consists of two branches. The main branch, the Eastern Rift Valley (often called the Great Rift Valley, or Rift Valley), extends along the entire length of the system. In the north the rift is occupied by the Jordan River, the Dead Sea, and the Gulf of Aqaba. It continues southward along the Red Sea and into the Ethiopian Denakil Plain to Lakes Rudolf (Turkana), Naivasha, and Magadi in Kenya. The rift is less obvious through Tanzania, because the eastern rim is much eroded, but it continues southward through the Shire River valley and Mozambique Plain to the coast of the Indian Ocean near Beira, Mozambique. The western branch of the system, the Western Rift Valley, extends northward from the northern end of Lake Nyasa (Lake Malawi) in a great arc that includes the Lakes Rukwa, Tanganyika, Kivu, Edward, and Albert (Mobuto Sese Seko). Most of the lakes in the rift system are deep and fjordlike, some with their floors well below sea level. The plateaus adjacent to the rift generally slope upward toward the valley and provide an average drop of from 2,000 to 3,000 feet (600 to 900 m) to the valley floor. In some places, such as the Gikuyu and Mau escarpments, the drop averages more than 9,000 feet (2,700 m). The rift has been forming for some 30,000,000 years (as Africa and the Arabian Peninsula separated) and has been accompanied by extensive volcanism along parts of its length, producing such massifs as Kilimanjaro and Mount Kenya.