Great Rift Valley
The subsidence of rock resulting from two or more parallel rocks moving apart is known as a graben. When this happens on a large scale, with tectonic plates moving apart, a rift valley is created.
Volcanic valley formed 10–20 million years ago owing to rifting (major subsidence through faulting) of part of the Earth's crust, and running about 8,000 km/5,000 mi from the Jordan Valley through the Red Sea to central Mozambique in southeast Africa. For most of its length the Rift Valley has a width of some 60 km/35 mi and, in highland areas especially, is bounded by inward-facing escarpments with a height which often reaches 500–1,000 m/1,500–3,000 ft. It is marked by a series of lakes, including Lake Turkana, and volcanoes, such as Mount Kilimanjaro. The rift system associated with the Rift Valley extends into northern Botswana, with geological faults controlling the location of the Okavango Delta.
| At some points its traces have been lost by erosion, but elsewhere, as in southern Kenya, boundary cliffs rise thousands of metres. |
| The shores of Lake Turkana are an important site for well-stratified remains of early humans; 2.5-million-year-old bones and tools have been found here. |
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