The Great Rift Valley
The Great Rift Valley runs for nearly 5000km down the eastern edge of Africa from Syria to Mozambique. Varying in depth from a few hundred metres to almost 3000m in Kenya's Mau Escarpment, it includes many well-known landmarks, from the Dead Sea to Lake Tanganyika.
The valley is the result of the gradual separation of the African and Arabian tectonic plates. It is likely that the process at work is like the opening of the Atlantic about 200 million years ago. But it is not such a simple structure as the Mid-Atlantic Ridge.
In East Africa, it is a comparatively simple boundary at which two plates, the Nubian and Somalian, are splitting apart. But where the Rift meets the Red Sea, these two plates come up against the Arabian plate, making a triple junction. In time, the three plates could separate and leave present-day East Africa as an island, much as the opening of the Red Sea has split Saudi Arabia from Africa. In the meantime, volcanoes, hot springs and other symptoms of the Earth beneath are rife along the Rift.