Where is the Great Rift Valley?

mt. kilimanjaro, at dawn, tanzania
Mount Kilimanjaro was formed from the Great Rift Valley. Richard Packwood/Getty Images

The Rift Valley, also known as the Great Rift Valley or Eastern Rift Valley, is a geological feature due to the movement of tectonic plates and mantle plumes that runs south from Jordan in southwest Asia, through East Africa and down to Mozambique in southern Africa.

In all the Rift Valley is 4000 miles (6,400 km) long and is 35 miles (64 km) wide on average. It is 30 million years old and exhibits extensive volcanism, having produced Mount Kilimanjaro and Mount Kenya.

The Great Rift Valley is a series of connected rift valleys. Seafloor spreading at the north end of the system created the Red Sea, separating the Arabian Peninsula on the Arabian Plate from the African continent on the Nubian African Plate and will eventually connect the Red Sea and the Mediterranean Sea.

The rifts on the African continent are in two branches and are slowly splitting the horn of Africa from the continent. It is thought that the rifting on the continent is driven by mantle plumes from deep in the earth, thinning crust so it may eventually form a new mid-ocean ridge as eastern Africa is split from the continent. The thinning of the crust has allowed the formation of volcanoes, hot springs, and deep lakes along the rift valleys.

Eastern Rift Valley

There are two branches of the complex. The Great Rift Valley or Rift Valley runs for the full extent, from Jordan and the Dead Sea to the Red Sea and across into Ethiopia and the Denakil Plain. Next, it goes through Kenya (particularly Lakes Rudolf (Turkana), Naivasha, and Magadi, into Tanzania (where because of erosion of the eastern edge it is less obvious), along the Shire River Valley in Malawi, and finally into Mozambique, where it reaches the Indian Ocean near to Beira.

Western Branch of the Rift Valley

The western branch of the Rift Valley, known as the Western Rift Valley, runs in a great arc through the Great Lakes region, passing along lakes Albert (also known as Lake Albert Nyanza), Edward, Kivu, Tanganyika, Rukwa, and to Lake Nyasa in Malawi. Most of these lakes are deep, some with bottoms below sea level.

The Rift Valley varies mostly between 2000 and 3000 feet (600 to 900 meters) in depth, with a maximum of 8860 feet (2700 meters) at the Gikuyu and Mau escarpments.

Fossils in the Rift Valleys

Many fossils showing the progress of human evolution have been found in the Rift Valley. In part, this is due to the conditions being favorable for preserving fossils. The escarpments, erosion, and sedimentation allow bones to be buried and preserved to be discovered in the modern era. The valleys, cliffs, and lakes may have played a role in bringing together different species in a variety of environments which would spur evolutionary change. While early humans likely lived in other locations in Africa and even beyond, the Rift Valley has conditions that allow archaeologists to discover their preserved remains.

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Boddy-Evans, Alistair. "Where is the Great Rift Valley?" ThoughtCo, Sep. 3, 2021, thoughtco.com/great-rift-valley-43920. Boddy-Evans, Alistair. (2021, September 3). Where is the Great Rift Valley? Retrieved from https://www.thoughtco.com/great-rift-valley-43920 Boddy-Evans, Alistair. "Where is the Great Rift Valley?" ThoughtCo. https://www.thoughtco.com/great-rift-valley-43920 (accessed March 31, 2023).