Africa's Great Rift Valley is a 9,656-km long fissure in the earth's crust, stretching from Lebanon to Mozambique. One of its most dramatic sections slices through East Africa, dividing Kenya into two segments. The Rift Valley was formed by violent subterranean forces that tore apart the earth's crust. These forces caused huge chunks of the crust to sink between parallel fault lines and force up molten rock in volcanic eruptions. Evidence that this process, called rifting, is still in progress comes from the many active and semi-active volcanoes, located along the Rift. Evidence of volcanic activity along the rift is provided by the presence of numerous boiling hot springs. The Great Rift Valley is a name given in the late 19th century by British explorer John Walter Gregory to the continuous geographic trough, approximately 6,000 kilometres (3,700 mi) in length, that runs from northern Syria in Southwest Asia to central Mozambique in East Africa. The name continues in some usages, although it is today considered geologically imprecise as it includes what are today regarded as separate, since 1869 due to the Suez Canal Company project, although related rift and fault systems. Today, the term is most often used to refer to the valley of the East African Rift, the divergent plate boundary which extends from the Afar Triple Junction southward across eastern Africa, and is in the process of splitting the African Plate into two new separate plates. Geologists generally refer to these incipient plates as the Nubian and Somalian subplates or protoplates. The Great Rift Valley as originally described extends from Lebanon in the north to Mozambique in the south, and constitutes one of two distinct physiographic provinces of the East African Highlands physiographic division. The northernmost part of the Rift, today called the Dead Sea Transform or Rift, forms the Beqaa Valley in Lebanon separating the Lebanon Mountains and Anti-Lebanon Mountains. Further south it is known as the Hula Valley separating the Galilee mountains and the Golan Heights. The River Jordan begins here and flows southward through Lake Hula into the Sea of Galilee in Israel, then continues south through the Jordan Valley into the Dead Sea on the Israeli-Jordanian border. From the Dead Sea southwards, the Rift is occupied by the Wadi Arabah, then the Gulf of Aqaba, and then the Red Sea. Off the southern tip of Sinai in the Red Sea, the Dead Sea Transform meets the Red Sea Rift which runs the length of the Red Sea. The Red Sea Rift comes ashore to meet the East African Rift and the Aden Ridge in the Afar Depression of East Africa. The junction of these three rifts is called the Afar Triple Junction.
In eastern Africa the valley divides into two, the Western Rift Valley and the Eastern Rift Valley. The Western Rift, also called the Albertine Rift, is edged by some of the highest mountains in Africa, including the Virunga Mountains, Mitumba Mountains, and Ruwenzori Range. It contains the Rift Valley lakes, which include some of the deepest lakes in the world (up to 1,470 meters deep at Lake Tanganyika). Lake Victoria, the second largest area freshwater lake in the world, is considered part of the Rift Valley system although it actually lies between the two branches. All of the African Great Lakes were formed as the result of the rift, and most lie within its rift valley. In Kenya the valley is deepest to the north of Nairobi. As the lakes in the Eastern Rift have no outlet to the sea and tend to be shallow they have a high mineral content as the evaporation of water leaves the salts behind. For example, Lake Magadi has high concentrations of soda (sodium carbonate) and Lake Elmenteita, Lake Bogoria, and Lake Nakuru are all strongly alkaline, while the freshwater springs supplying Lake Naivasha are essential to support its current biological variety. Africa's Great Rift Valley is a 6,000-mile crack (fissure) in the earth's crust, stretching from Lebanon to Mozambique. One of its most dramatic sections slices through East Africa, dividing Kenya into two segments. Geologists know that the Rift Valley was formed by violent subterranean forces that tore apart the earth's crust. These forces caused huge chunks of the crust to sink between parallel fault lines and force up molten rock in volcanic eruptions. Evidence that this process, called rifting, is still in progress comes from the many active and semi-active volcanoes, located along the Rift. Evidence of volcanic activity along the rift is provided by the presence of numerous boiling hot springs.
Great Rift Valley, geological fault system of SW Asia and E Africa. It extends c.3,000 mi (4,830 km) from N Syria to central Mozambique. The northernmost extension runs S through Syria and Lebanon, the Jordan valley, the Dead Sea, and the Gulf of Aqaba. It continues into the trough of the Red Sea and at the southern end branches into the Gulf of Aden, where it continues as part of the Mid-Oceanic Ridge of the Indian Ocean. The main section of the valley in Africa continues from the Red Sea SW across Ethiopia and S across Kenya, Tanzania, and Malawi to the lower Zambezi River valley in Mozambique. Many small lakes in Ethiopia and several long narrow lakes, notably lakes Turkana and Nyasa, lie on its course. Just N of Lake Nyasa there is a western branch, which runs north, chiefly along the eastern border of Congo (Kinshasa); this branch is marked by a chain of lakes, including lakes Tanganyika, Kivu, Edward, and Albert (Mobutu). Lake Victoria does not lie in the Great Rift Valley but between its main and western branches. The Great Rift Valley ranges in elevation from c.1,300 ft (395 m) below sea level (the Dead Sea) to c.6,000 ft (1,830 m) above sea level in S Kenya. Erosion has concealed some sections, but in places, notably in Kenya, there are sheer cliffs several thousand feet high. The present configuration of the rift, which dates from the mid-Pleistocene epoch, is probably a result of a rifting process associated with thermal currents in the earth's mantle (see rift valley); there is evidence of earlier rift structures. In some places this natural divide is up to 100 km (60 miles) wide, while it reaches its narrowest point just north of Nairobi at 45 km wide. The valley floor is at its lowest near Lake Turkana where there is virtually no distinction between the Great Rift and the surrounding desert. As it heads south, however, the valley walls form sheer cliffs rising to 1,900 km (6,232 ft) at Lake Naivasha. After Naivasha, the valley descends again to 580 meters (1,902 feet) at the Tanzanian border.
