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The Great Rift Valley is a name given in the late 19th century by British explorer John Walter Gregory to the continuous geographic trench, approximately in length, that runs from northern Syriamarker in Southwest Asia to central Mozambiquemarker in East Africa. The name continues in some usages, although it is today considered geologically imprecise as it combines features that are today regarded as separate, 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 Plate and the Somali Plate.

Geography

The Great Rift Valley as originally described extends from Lebanonmarker in the north to Mozambiquemarker in the south, and constitutes one of two distinct physiographic provinces of the East African mountains 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 Mountainsmarker. Further south it is known as the Hula Valleymarker separating the Galilee mountains and the Golan Heightsmarker. The River Jordanmarker begins here and flows southward through Lake Hulamarker into the Sea of Galileemarker in Israelmarker, then continues south through the Jordan Rift Valley into the Dead Seamarker on the Israelimarker-Jordanianmarker border. From the Dead Sea southwards, the Rift is occupied by the Wadi Arabahmarker, then the Gulf of Aqabamarker, and then the Red Seamarker. 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 Depressionmarker 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 Mountainsmarker, Mitumba Mountainsmarker, and Ruwenzori Rangemarker. It contains the Rift Valley lakes, which include some of the deepest lakes in the world (up to 1,470 metres deep at Lake Tanganyikamarker). Lake Victoriamarker, 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 Lakesmarker were formed as the result of the rift, and most lie within its rift valley.

In Kenyamarker, the valley is deepest to the north of Nairobimarker. 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 Magadimarker has high concentrations of soda (sodium carbonate) and Lake Elmenteitamarker, Lake Bogoriamarker, and Lake Nakurumarker are all strongly alkaline, while the freshwater springs supplying Lake Naivashamarker are essential to support its current biological variety.

Discoveries in human evolution

The Rift Valley in East Africa has been a rich source of fossilsthat allow study of human evolution, especially in an area known as Piedmont.

Because the rapidly eroding highlands have filled the valley with sediments, a favorable environment for the preservation of remains has been created. The bones of several hominid ancestors of modern humans have been found there, including those of "Lucy", a partial, yet eye opening australopithecine skeleton, which was discovered by anthropologist Donald Johanson dating back over 3 million years. Richard and Mary Leakey have also done significant work in this region.

More recently, two other hominid ancestors have been discovered there: a 10 million year-old ape called Chororapithecus abyssinicus, found in the Afar rift, in eastern Ethiopia, and the Nakalipithecus nakayamai, which is also 10 million years old.

Further reading

  • Africa's Great Rift Valley, 2001, ISBN 0810906023
  • Tribes of the Great Rift Valley, 2007, ISBN 9780810994119
  • East African Rift Valley lakes, 2006, OCLC 76876862
  • Photographic atlas of the Mid-Atlantic Ridge Rift Valley, 1977, ISBN 0387902473
  • Rift Valley fever : an emerging human and animal problem, 1982, ISBN 9241700637


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