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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.
Exploration of the geology of the West Antarctic Rift is difficult, because, apart from peaks of the Transantarctic Mountains that protrude above the ice, the region is covered by the vast West Antarctic Ice Sheet. Thus, the rift 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.
Although many rifts within the West Antarctic Rift system are no longer active, it is now known that West Antarctica is moving away from the East Antarctic Craton in a north/northeasterly direction (approximately in the direction of the South Georgia Islands) at a rate of about 2 mm per year or 500,000 years per kilometre.
The West Antarctic Rift is the source of all the recently active volcanoes within Antarctica, and of most of the major Antarctic mountain systems outside the Antarctic Peninsula. It is also believed to have a major influence on ice flows in West Antarctica, because fast moving ice streams are believed to be influenced by the lubrication provided by water-saturated till, which some argue could help cause breakup of the ice sheet if global warming accelerates.