A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault. A rift valley is formed on a divergent plate boundary, a crustal extension, a spreading apart of the surface, which is subsequently further deepened by the forces of erosion.
USGS Plates cover the entire Earth, and their boundaries play an important role in geologic happenings. The movement of these plates atop a thick, fluid "mantle" is known as plate tectonics and is the source of earthquakes and volcanoes. Plates crash together to make mountains, such as the Himalayas.Apr 6, 2014