East African Rift

A map of East Africa showing some of the historically active volcanoes (as red triangles) and the Afar Triangle (shaded at the center), which is a so-called triple junction (or triple point) where three plates are pulling away from one another: the Arabian Plate and two parts of the African Plate—the Nubian and Somali—splitting along the East African Rift Zone.

The East African Rift is an active continental rift zone in eastern Africa that appears to be a developing divergent tectonic plate boundary. In the past it was considered to be part of a larger Great Rift Valley that extended north to Turkey. The rift is a narrow zone in which the African Plate is in the process of splitting into two new tectonic plates called the Somali Plate and the Nubian Plate, which are subplates or protoplates.

Extent

The East African Rift runs from the Afar Triple Junction in the Afar Depression southward through eastern Africa. It is believed to run offshore of the coast of Mozambique along the Kerimba and Lacerda rifts or grabens, terminating in the Andrew Bain Fracture Zone complex, where it is believed to have its junction with the Southwest Indian Ridge.

The East African Rift consists of two main branches called the Gregory Rift and the Western Rift Valley. These result from the actions of numerous normal (dip-slip) faults which are typical of all tectonic rift zones. The Eastern Rift Valley 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 further south the valley of Lake Malawi.

Volcanic activity

The East African Rift Zone includes a number of active as well as dormant volcanoes. These include Mount Kilimanjaro, Mount Kenya, Mount Longonot, Menengai Crater, Mount Karisimbi, Mount Nyiragongo, Mount Meru and Mount Elgon as well as the Crater Highlands in Tanzania. The Ol Doinyo Lengai volcano remains active, and is currently the only natrocarbonatite volcano in the world. Erta Ale is a continuously active basaltic shield volcano in the Afar Region of northeastern Ethiopia.

Discoveries in human evolution

Main articles: Human evolution and Timeline of human evolution

The Rift Valley in East Africa has been a rich source of fossils that allow study of human evolution.

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.

See also

• Baikal Rift Zone
• West Antarctic Rift
• Northern Cordilleran Volcanic Province