The biggest gash in the Earth’s surface on land is the Great Rift Valley. This series of rifts runs from the eastern Mediterranean southeast through the Dead Sea and Red Sea, then south across East Africa through Lake Turkana. It divides around Lake Victoria to continue south to Lake Tanganyika and Lake Malawi. The entire valley system is some 5000 kilometres (3000 miles) long and widens by up to two centimetres (nearly an inch) in places every year. In millions of years' time, the Red Sea will open up to become a broad ocean, while waters from the Indian Ocean may flood into the valley.

Formation

A giant block of crust, hundreds of kilometres wide in places, has, over millions of years, dropped down between gigantic faults. On each side, high cliffs tower above the valley floor; here, the rocks have been bent into folds, with some almost tipped right over. Volcanoes spew out lava, red-hot liquid rock from deep inside the Earth that has forced its way up through the cracks.

One day, an arm of the Indian Ocean might fill the valley, turning East Africa into an island. This has already happened in a stretch of the valley to the north, now lying beneath the Red Sea. The Red Sea is gradually widening as new volcanic rocks push up at its centre. Eventually, sea-floor spreading will turn it into a broad ocean.