The Great Rift Valley lies between the Ethiopian Plateau to the north and the Somalia Plateau to the south. The
rift developed as the
Nubian and
Somali plates began to separate during the
Miocene Period along the East African rift system. Rift initiation was asynchronous along the Ethiopian rift valley: deformation began around 18 million years ago at the south end, around 11 million years ago close to the Afar depression and probably around 6-8 million years ago in the central sector. The rift is extending in an ESE-WNW direction at about annually. The Ethiopian rift valley is about wide and bordered on both margins by large, discontinuous
normal faults that give rise to major tectonic escarpments separating the rift floor from the surrounding plateaus. These faults are now thought to be inactive at the northern rift valley termination, whereas to the south they are still tectonically and seismically active. The rift floor is cut by a series of smaller en echelon, right-stepping, rift basins of
Quaternary to recent age. These basins are about wide and long. In the northern part of the rift, extension within the valley is now thought to be mainly along these faulted and
magmatically active segments. These segments are considered to be developing
mid ocean ridge spreading centers. == Ethiopian Rift Valley lakes ==