The Great Rift Valley is a name given to the continuous geographical trench, about 6,000 kilometers (3,700 mi) in length, that runs from northern Syria in Southwest Asia to central Mozambique in East Africa. The rift is bordered by a series of mountains and active volcanoes. It is a site of faults and earthquakes.
Basically, the western part of Africa is drifting away from the eastern part body. This causes all the geological activity at the Valley. Far in the future, a sea will run between these two parts of Africa. The Arabian peninsula is already almost separated. The whole process is part of plate tectonics. In eastern Africa, the valley divides into two, the Western Rift Valley and the Eastern Rift Valley.
There are about 20 UNESCO World Heritage Sites which owe their formation to the geography and geology of the Great Rift Valley.