Antarctica continent and West Antarctic Rift

The West Antarctic Rift System is a series of rift valleys between

East East 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 fact that ea ...

and West Antarctica. 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 high ...

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 Martin 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 Antarctica. ...

. 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 United States physiographic region, physiographic region covering much of the inland Western United States and Northern Mexico, northwestern Mexico. It is defined by unique basin and range topography, charac ...

of the

Western United States The Western United States (also called the American West, the Western States, the Far West, the Western territories, and the West) is List of regions of the United States, census regions United States Census Bureau. As American settlement i ...

Geology

Exploration of the geology of the West Antarctic Rift System is limited because apart from peaks of the

Transantarctic Mountains The Transantarctic Mountains (abbreviated TAM) comprise a mountain range of uplifted rock (primarily sedimentary) in Antarctica which extends, with some interruptions, across the continent from Cape Adare in northern Victoria Land to Coats L ...

that protrude above the ice, much of the region is covered by the Ross Ice Shelf and the vast

West Antarctic Ice Sheet The West Antarctic Ice Sheet (WAIS) is the segment of the Antarctic ice sheet, continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere. It is cla ...

. 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 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. It was formerly considered to be part of a l ...

, 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 am ...

Evolution

Rifting began in the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

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 epoch (geology), 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 mea ...

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

Zealandia Zealandia (pronounced ), also known as (Māori language, Māori) or Tasmantis (from Tasman Sea), is an almost entirely submerged continent, submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83� ...

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 (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

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

and

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

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 ...

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 Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

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), as well as the current and most recent of the twelve periods of the ...

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 South Georgia and the South Sandwich Islands (SGSSI) is a British Overseas Territory in the southern Atlantic Ocean. It is a remote and inhospitable collection of islands, consisting of South Georgia and a chain of smaller islands known as the S ...

) 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 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 Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...

accelerates.

References

{{Reflist

External links

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