The Great Rift Valley describes a large trench system in Eastern Africa that stretches through Ethiopia, Kenya, Uganda and Somalia. The fracture is a result of tectonic plate movement within the Earth's crust. The East African Rift System is a divergent rift, meaning that the plates are moving apart.
In historical geology, the Great Rift Valley referred to a larger rift that spanned from Madagascar all the way into Syria. Geologists are now aware that the rifts are separate from one another though part of the same larger system. In East Africa, the main components are the Nubian Plate, the Ethiopian Dome, the Somalian Plate and the Kenyan Dome.