West Antarctic Rift
Encyclopedia
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-craton
ic 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Although many rifts within the West Antarctic Rift system are no longer active, it is now known that West Antarctica is moving away from the East Antarctic Craton in a north/northeasterly direction (approximately in the direction of the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.
East Antarctica
East Antarctica, also called Greater Antarctica, constitutes the majority of the Antarctic continent, lying on the Indian Ocean side of the Transantarctic Mountains...
and West Antarctica
West Antarctica
West Antarctica, or Lesser Antarctica, one of the two major regions of Antarctica, is the part of the continent that lies within the Western Hemisphere including the Antarctic Peninsula.-Location and description:...
. It encompasses the Ross Sea
Ross Sea
The Ross Sea is a deep bay of the Southern Ocean in Antarctica between Victoria Land and Marie Byrd Land.-Description:The Ross Sea was discovered by James Ross in 1841. In the west of the Ross Sea is Ross Island with the Mt. Erebus volcano, in the east Roosevelt Island. The southern part is covered...
, the area under the Ross Ice Shelf
Ross Ice Shelf
The Ross Ice Shelf is the largest ice shelf of Antarctica . It is several hundred metres thick. The nearly vertical ice front to the open sea is more than 600 km long, and between 15 and 50 metres high above the water surface...
and a part of West Antarctica. Its evolution is due to lithospheric thinning of the non-craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...
ic area of West Antarctica.
Exploration of the geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
of the West Antarctic Rift is difficult, because, apart from peaks of the Transantarctic Mountains
Transantarctic Mountains
The three largest mountain ranges on the Antarctic continent are the Transantarctic Mountains , the West Antarctica Ranges, and the East Antarctica Ranges. The Transantarctic Mountains compose a mountain range in Antarctica which extend, with some interruptions, across the continent from Cape Adare...
that protrude above the ice, the region is covered by the vast West Antarctic Ice Sheet
West Antarctic Ice Sheet
The West Antarctic Ice Sheet is the segment of the continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains which lies in the Western Hemisphere. The WAIS is classified as a marine-based ice sheet, meaning that its bed lies well...
. Thus, the rift is less well known than other major rift valleys. It is known, however, that like the East African Rift
East African Rift
The East African Rift is an active continental rift zone in eastern Africa that appears to be a developing divergent tectonic plate boundary. It is part of the larger Great Rift Valley. The rift is a narrow zone in which the African Plate is in the process of splitting into two new tectonic plates...
, 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
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
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
Berkner Island
Berkner Island or Berkner Ice Rise or Hubley Island is a high and completely ice-covered large island about long and wide in Antarctica, with an area of . It is the second largest island of both Antarctica and the British Antarctic Territory, after Alexander Island. It is also located within the...
.
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
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
. 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
Till
thumb|right|Closeup of glacial till. Note that the larger grains in the till are completely surrounded by the matrix of finer material , and this characteristic, known as matrix support, is diagnostic of till....
, which some argue could help cause breakup of the ice sheet if global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
accelerates.
External links
- Map of the West Antarctic Rift System and Transantarctic Mountains
- Winberry, J. P., and S. Anandakrishnan, 2004, Crustal structure of the West Antarctic rift system and Marie Byrd Land hotspot. Geology. v. 32, no. 11, pp. 977–980. DOI: 10.1130/G20768.1