The West Antarctic Rift is a major, active rift valley lying between East and West Antarctica. It encompasses the Ross Sea, the area under the Ross Ice Shelf and a part of West Antarctica. Its evolution is due to lithospheric thinning of the non-cratonic area of West Antarctica.
Because, apart from peaks of the Transantarctic Mountains that protrude above the ice, the region is covered by the vast West Antarctic Ice Sheet, it is very difficult to explore the geology of the West Antarctic Rift, so that it is less well known than other major rift valleys. It is known, however, that like the East African Rift, the West Antarctic Rift is actually a number of much shorter rifts that cross Antarctica. There is also a sharp division between older, broader Paleogene rifts including the Ross Sea Basin and the younger, narrower Terror Rift. There are also a large number of failed rifts extending as far as Berkner Island.