A rift valley is a linear lowland region that forms where Earths tectonic plates move apart, or rift. It is produced by the action of a geologic rift, which is formed as a result of the pulling apart of the lithosphere due to extensional tectonics. Rift valleys can occur at all elevations, from the sea floor to plateaus and mountain ranges in continental crust or in oceanic crust. They are often associated with a number of adjoining subsidiary or co-extensive valleys, which are typically considered part of the principal rift valley geologically. Rift valleys are found on land and at the bottom of the ocean, where they are created by the process of seafloor spreading. They differ from river valleys and glacial valleys in that they are created by tectonic activity and not the process of erosion. The most well-known rift valley on Earth is the Great Rift Valley, which stretches from the Middle East in the north to Mozambique in the south and is the result of the splitting of the African Plate into two new and separate plates.