Antarctica continent and West Antarctic Rift

The West Antarctic Rift System is a series of

rift valleys A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear dep ...

between

East East or Orient is one of the four cardinal directions or points of the compass. It is the opposite direction from west and is the direction from which the Sun rises on the Earth. Etymology As in other languages, the word is formed from the fac ...

and

West Antarctica West Antarctica, or Lesser Antarctica, one of the two major regions of Antarctica, is the part of that continent that lies within the Western Hemisphere, and includes the Antarctic Peninsula. It is separated from East Antarctica by the Transan ...

. It encompasses the Ross Embayment, the

Ross Sea The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who ...

, the area under the

Ross Ice Shelf The Ross Ice Shelf is the largest ice shelf of Antarctica (, an area of roughly and about across: about the size of France). It is several hundred metres thick. The nearly vertical ice front to the open sea is more than long, and between h ...

and a part of

Marie Byrd Land Marie Byrd Land (MBL) is an unclaimed region of Antarctica. With an area of , it is the largest unclaimed territory on Earth. It was named after the wife of American naval officer Richard E. Byrd, who explored the region in the early 20th centu ...

in West Antarctica, reaching to the base of the

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

. It has an estimated length of and a width of approximately . Its evolution is due to lithospheric thinning of an area of Antarctica that resulted in the demarcation of East and West Antarctica. The scale and evolution of the rift system has been compared to that of the

Basin and Range Province The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating ...

of the

Western United States The Western United States (also called the American West, the Far West, and the West) is the region comprising the westernmost states of the United States. As American settlement in the U.S. expanded westward, the meaning of the term ''the We ...

Geology

Exploration of the geology of the West Antarctic Rift System is limited because apart from peaks of the Transantarctic Mountains that protrude above the ice, much of the region is covered by the Ross Ice Shelf and the vast West Antarctic Ice Sheet. Several mountain ranges are located at the eastern boundary in Marie Byrd Land. Consequently, the rift is less well known than other major rift valley systems. It is known, however, that like the

East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of ...

, the West Antarctic Rift System comprises a number of much shorter rifts that cross Antarctica. Beneath the floor of the Ross Sea four rift basins have been detected by marine seismic reflections surveys. Rift basins have been mapped under the West Antarctic Ice Sheet including the

Bentley Subglacial Trench The Bentley Subglacial Trench is a vast topographic trench in Marie Byrd Land, West Antarctica, 80°S, 115°W. At 2,555 meters (8,382 ft) below sea level, it (along with the deepest points within the adjacent Byrd Subglacial Basin) is a ...

Evolution

Rifting began in the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

as a result of tectonic extension (stretching and thinning of the crust and mantle) in approximately an east–west orientation, by plate tectonics processes. The extension within the Ross Embayment occurred over four time periods and totals 500 kilometers or more, mostly before the late

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

. The first phase happened in the east near Marie Byrd Land before the Campbell Plateau of

Zealandia Zealandia (pronounced ), also known as (Māori) or Tasmantis, is an almost entirely submerged mass of continental crust that subsided after breaking away from Gondwanaland 83–79 million years ago.Gurnis, M., Hall, C.E., and Lavier, L.L., ...

broke away from Antarctica in the Late Cretaceous. A second phase during the Late Cretaceous and

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pala ...

extended the central areas of the embayment. This extension was at least 130 kilometers. A third phase is related to 170–180 kilometers of

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

and

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...

seafloor spreading Seafloor spreading or Seafloor spread is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. History of study Earlier theories by Alfred Wegener a ...

in the western parts of the embayment on the Adare Trough or basin in the deep-sea. This episode of sea floor spreading created the ocean crust that now underlies much of the Northern Basin. This phase also resulted in extension of the Victoria Land Basin (95 km). A small amount of extension (~7 kilometers) occurred in the Adare basin and Victoria Land Basin (10-15 kilometers) in a fourth phase during Miocene time. Displacement including minor extension in the western WARS and Ross Embayment computed from reconstruction of oceanic magnetic anomalies ended 11 million years ago. During the Eocene to Miocene clockwise relative rotation of West Antarctica with respect to East Antarctica resulted in extension in the western Ross Embayment but contraction, in Marie Byrd Land of West Antarctica. Subsidence to form the present topography of the embayment continued through the

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...

as the extended crust and mantle under the Ross Embayment cooled. Faulting within the Terror Rift, located in the Victoria Land Basin, continued after 11 Ma, and probably into or through

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million year ...

time. Although most rifts within the West Antarctic Rift System are no longer active, geodetic surveys show that West Antarctica is moving away from East Antarctica in a north/northeasterly direction (approximately in the direction of the

South Georgia Islands ) , anthem = "God Save the King" , song_type = , song = , image_map = South Georgia and the South Sandwich Islands in United Kingdom.svg , map_caption = Location of South Georgia and the South Sandwich Islands in the southern Atlantic Oce ...

) at a rate of not greater than 1- or . The West Antarctic Rift System is the source of all the recently active volcanoes within Antarctica and all the recently active volcanoes on the continent. It is responsible for most of the major mountain systems outside the

. Volcanism has been attributed to the rifting and also a mantle hotspot.

Glaciology

The WARS is also believed to have a major influence on ice flows in West Antarctica. In western Marie Byrd Land active glaciers flow through fault-bounded valleys (grabens) of the WARS. Sub-ice volcanism has been detected and proposed to influence ice flow. Fast-moving ice streams in the

Siple Coast Siple Coast () is the middle portion of the relatively ill-defined coast along the east side of the Ross Ice Shelf, between the north end of Gould Coast () and the south end of Shirase Coast (). The area was originally called Kirton Coast, but was ...

adjacent to the east edge of the Ross Ice Shelf are influenced by the lubrication provided by water-saturated

till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

within fault-bounded grabens within the rift, which could cause rapid breakup of the ice sheet if

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

accelerates.

References

{{Reflist

External links

ROSETTA Project
Geology of Antarctica Mesozoic Antarctica Mesozoic rifts and grabens Cenozoic rifts and grabens Transantarctic Mountains West Antarctica