The West Antarctic Rift system (WARS) is a series of rift valleys lying between East and West Antarctica. It encompasses the Ross Embayment, the Ross Sea, the area under the Ross Ice Shelf and a part of Marie Byrd Land in West Antarctica, reaching to the base of the Antarctic Peninsula. It has an estimated length of 3000 km and a width of approximately 700 km. 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 of the western U.S.
Exploration of the geology of the West Antarctic Rift 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 West Antarctic Rift 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.
Rifting began in the late Cretaceous 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 first phase happened in the east near Marie Byrd Land before the Campbell Plateau of Zealandia broke away from Antarctica in the late Cretaceous.
A third phase is related to 170-180 kilometers of Eocene and Oligocene sea floor spreading 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 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 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) at a rate of not greater than 1-2 millimetres per year (0.079 in/year) or 500,000 years per kilometre (800,000 years per mile).
The West Antarctic Rift 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 Antarctic Peninsula. Volcanism has been attributed to the rifting and also a mantle hotspot.
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 within fault-bounded grabens within the rift, which could cause rapid breakup of the ice sheet if global warming accelerates.
The Adare Basin is a geologic structural basin located north-east of Cape Adare of Antarctica, for which its named, and north of the western Ross Sea. The Adare basin is an extensional rift basin located along a seafloor spreading center that forms the failed arm of the tertiary spreading ridge separating East and West Antarctica, known as the West Antarctic Rift System and similar in structure to The East Africa Rift System. Centrally located in the Adare Basin is the Adare Trough. The extension of this rift system is recorded in a series of magnetic anomalies which run along the seafloor at the extinct, north-south trending, Adare spreading axis. The Adare spreading system continues unbroken into the Northern Basin underlying the adjacent Ross Sea continental shelf.Antarctic Plate
The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau and extending outward under the surrounding oceans. After breakup from Gondwana (the southern part of the supercontinent Pangea), the Antarctic plate began moving the continent of Antarctica south to its present isolated location causing the continent to develop a much colder climate. The Antarctic Plate is bounded almost entirely by extensional mid-ocean ridge systems. The adjoining plates are the Nazca Plate, the South American Plate, the African Plate, the Somali Plate, the Indo-Australian Plate, the Pacific Plate, and, across a transform boundary, the Scotia Plate.
The Antarctic Plate has an area of about 60,900,000 km2 (23,500,000 sq mi). It is the Earth's fifth-largest plate.
The Antarctic Plate's movement is estimated to be at least 1 cm (0.4 in) per year towards the Atlantic OceanBell Buttress
Bell Buttress (77°18′15″S 160°59′30″E) is a forked flat-topped ridge, 1.2 nautical miles (2.2 km) long, which extends north from The Fortress in the Cruzen Range of Victoria Land, into the southwest part of Victoria Upper Névé. Named by the Advisory Committee on Antarctic Names in 2005 after Robin E. Bell, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY; aerogeophysical research of the lithosphere of the West Antarctic Rift system (CASERTZ), five field seasons 1991-99.
Bell Buttress is named after Robin Bell.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 among the lowest points on the surface of the Earth not covered by ocean, although it is covered by ice. (See Extremes on Earth and Vestfold Hills).
The trench was named in 1961 after Charles R. Bentley who was the geophysicist in charge of the scientific expeditions in West Antarctica in 1957–59 that led to its discovery.Starting in 2016 some hot anomalies were detected beneath Bentley Subglacial Trench and Mount Sidley volcano.Christine Siddoway
Christine Siddoway is an American Antarctic researcher, best known for her work on the geology and tectonics of the Ford Ranges in western Marie Byrd Land.Divergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts, which eventually become rift valleys. Most active divergent plate boundaries occur between oceanic plates and exist as mid-oceanic ridges. Divergent boundaries also form volcanic islands, which occur when the plates move apart to produce gaps that molten lava rises to fill.
Current research indicates that complex convection within the Earth's mantle allows material to rise to the base of the lithosphere beneath each divergent plate boundary.
This supplies the area with vast amounts of heat and a reduction in pressure that melts rock from the asthenosphere (or upper mantle) beneath the rift area, forming large flood basalt or lava flows. Each eruption occurs in only a part of the plate boundary at any one time, but when it does occur, it fills in the opening gap as the two opposing plates move away from each other.
Over millions of years, tectonic plates may move many hundreds of kilometers away from both sides of a divergent plate boundary. Because of this, rocks closest to a boundary are younger than rocks further away on the same plate.Geography of Antarctica
The geography of Antarctica is dominated by its south polar location and, thus, by ice. The Antarctic continent, located in the Earth's southern hemisphere, is centered asymmetrically around the South Pole and largely south of the Antarctic Circle. It is washed by the Southern (or Antarctic) Ocean or, depending on definition, the southern Pacific, Atlantic, and Indian Oceans. It has an area of more than 14 million km².
Some 98% of Antarctica is covered by the Antarctic ice sheet, the world's largest ice sheet and also its largest reservoir of fresh water. Averaging at least 1.6 km thick, the ice is so massive that it has depressed the continental bedrock in some areas more than 2.5 km below sea level; subglacial lakes of liquid water also occur (e.g., Lake Vostok). Ice shelves and rises populate the ice sheet on the periphery.
In September 2018, researchers at the National Geospatial-Intelligence Agency released a high resolution terrain map (detail down to the size of a car, and less in some areas) of Antarctica, named the "Reference Elevation Model of Antarctica" (REMA).Geology of Antarctica
The geology of Antarctica covers the geological development of the continent through the Proterozoic Eon, Paleozoic, Mesozoic and Cenozoic eras.
More than 170 million years ago, Antarctica was part of the supercontinent Gondwana. Over time Gondwana broke apart and Antarctica as we know it today was formed around 35 million years ago.List of largest rifts, canyons and valleys in the Solar System
Following are the longest, widest, and deepest rifts and valleys in various worlds of the Solar System.Rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics.Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben with normal faulting and rift-flank uplifts mainly on one side. Where rifts remain above sea level they form a rift valley, which may be filled by water forming a rift lake. The axis of the rift area may contain volcanic rocks, and active volcanism is a part of many, but not all active rift systems.
Major rifts occur along the central axis of most mid-ocean ridges, where new oceanic crust and lithosphere is created along a divergent boundary between two tectonic plates.
Failed rifts are the result of continental rifting that failed to continue to the point of break-up. Typically the transition from rifting to spreading develops at a triple junction where three converging rifts meet over a hotspot. Two of these evolve to the point of seafloor spreading, while the third ultimately fails, becoming an aulacogen.Rift valley
A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault. A rift valley is formed on a divergent plate boundary, a crustal extension or spreading apart of the surface, which is subsequently further deepened by the forces of erosion. When the tensional forces are strong enough to cause the plate to split apart, a center block drops between the two blocks at its flanks, forming a graben. The drop of the center creates the nearly parallel steeply dipping walls of a rift valley when it is new. That feature is the beginning of the rift valley, but as the process continues, the valley widens, until it becomes a large basin that fills with sediment from the rift walls and the surrounding area. One of the best known examples of this process is the East African Rift. On Earth, rifts can occur at all elevations, from the sea floor to plateaus and mountain ranges in continental crust or in oceanic crust. They are often associated with a number of adjoining subsidiary or co-extensive valleys, which are typically considered part of the principal rift valley geologically.Ross Embayment
The Ross Embayment is a large region of Antarctica, comprising the Ross Ice Shelf and the Ross Sea, that lies between East and West Antarctica.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 Ross who visited this area in 1841. To the west of the sea lies Ross Island and Victoria Land, to the east Roosevelt Island and Edward VII Peninsula in Marie Byrd Land, while the southernmost part is covered by the Ross Ice Shelf, and is about 200 miles (320 km) from the South Pole. Its boundaries and area have been defined by the New Zealand National Institute of Water and Atmospheric Research as having an area of 637,000 square kilometres (246,000 sq mi).The circulation of the Ross Sea is dominated by a wind-driven ocean gyre and the flow is strongly influenced by three submarine ridges that run from southwest to northeast. The circumpolar deep water current is a relatively warm, salty and nutrient-rich water mass that flows onto the continental shelf at certain locations. The Ross Sea is covered with ice for most of the year.
The nutrient-laden water supports an abundance of plankton and this encourages a rich marine fauna. At least ten mammal species, six bird species and 95 fish species are found here, as well as many invertebrates, and the sea remains relatively unaffected by human activities. New Zealand has claimed that the sea comes under its jurisdiction as part of the Ross Dependency. Marine biologists consider the sea to have a high level of biological diversity and it is the site of much scientific research. It is also the focus of some environmentalist groups who have campaigned to have the area proclaimed as a world marine reserve. In 2016 an international agreement established the region as a marine park.Royal Society Range
The Royal Society Range (78°10′S 162°40′E) is a majestic mountain range in Victoria Land, Antarctica. With its summit at 4,025 metres (13,205 ft), the massive Mount Lister forms the highest point in this range. Mount Lister is located along the western shore of McMurdo Sound between the Koettlitz, Skelton and Ferrar glaciers. Other notable local terrain features include Allison Glacier, which descends from the west slopes of the Royal Society Range into Skelton Glacier.Tectonic evolution of the Transantarctic Mountains
The tectonic evolution of the Transantarctic Mountains appears to have begun when Antarctica broke away from Australia during the late Cretaceous and is ongoing, creating along the way some of the longest mountain ranges (at 3500 kilometers) formed by rift flank uplift and associated continental rifting. The Transantarctic Mountains (TAM) separate East and West Antarctica. The rift system that formed them is caused by a reactivation of crust along the East Antarctic Craton. This rifting or seafloor spreading causes plate movement that results in a nearby convergent boundary which then forms the mountain range. The exact processes responsible for making the Transantarctic Mountains are still debated today. This results in a large variety of proposed theories that attempt to decipher the tectonic history of these mountains.Toney Mountain
Toney Mountain is an elongated snow-covered shield volcano, 60 km (38 mi) long and rising to 3,595 m in Richmond Peak, located 56 km (35 mi) SW of Kohler Range in Marie Byrd Land, Antarctica.Toney Mountain is an elongated volcanic massif that rises from a basaltic plateau. A 3 km-wide summit caldera tops the volcano, and is elongated in east-west direction; this orientation is shared with calderas on other volcanoes in Marie Byrd Land and reflects regional tectonic stress. The slopes of the volcano feature parasitic vents and glacial corries, and are much steeper north of the volcano than south of it. Most of the mountain is covered by ice and its eastern sector may be a crater. That the mountain is mostly ice covered makes it difficult to determine its composition, the origin of the elongated shape of the volcano and the volcanological relation between the parasitic cinder cones and the main volcanic pile. Its volume may be about 2,800 cubic kilometres (670 cu mi).The plateau and parasitic cones are formed by hawaiite and the few outcrops on the main volcano by benmoreite and comendite. They contain phenocrysts of olivine, plagioclase, pyroxene and titanaugite in the former and of clinopyroxene, feldspar and olivine.An age of 9.1 million years ago has been obtained on a basaltic lava flow beneath the volcano, and it has been inferred that the basal plateau formed between 10.1 and 9.1 million years ago. The massif is younger, with ages ranging from 1 million years in its lower parts to 500,000 years ago. Holocene eruptions may have also occurred at Toney Mountain as indicated by 30 kyr ash layers in ice cores from Byrd Station, although Mount Takahe and Mount Waesche are also candidates. During that time period, a number of volcanic eruptions occurred in Antarctica as recorded by ash layers in ice; this coincides with the coldest period of the Wisconsin glaciation and it is possible that the effects of ash clouds from the Antarctic eruptions caused this period of cold global temperatures. On the other hand, it is also possible that growing ice sheets during this period compressed magma chambers and thus triggered explosive eruptions.Toney Mountain lies in Marie Byrd Land, a tectonically and volcanically active region of Antarctica. There, a layer of basaltic rocks up to 5 kilometres (3.1 mi) thick underlie a series of felsic volcanic edifices. These basaltic rocks in turn are emplaced above a Paleozoic basement with granite intrusions of Devonian-Cretaceous, which crops out in some mountain ranges. Beneath Toney Mountain, the basaltic floor rises from an elevation of 3 kilometres (1.9 mi) beneath sea level, and the volcano is situated on the floor of a graben. The region is further characterized by a 500 by 1,200 kilometres (310 mi × 750 mi) large dome-like uplift, part of the West Antarctic Rift, and it may reflect the presence of a stationary hotspot.Toney Mountain was probably among those viewed from a distance by Admiral Byrd and others of the USAS in plane flights from the ship Bear in February 1940. It was mapped in December 1957 by the oversnow traverse party from Byrd Station to the Sentinel Range, 1957–58, led by C.R. Bentley who proposed the name. Named after George R. Toney, scientific leader at Byrd Station in 1957, a participant in several Antarctic and Arctic operations, serving in both field and administrative capacities.Transantarctic Mountains
The Transantarctic Mountains (abbreviated TAM) comprise a mountain range of uplifted sedimentary rock in Antarctica which extend, with some interruptions, across the continent from Cape Adare in northern Victoria Land to Coats Land. These mountains divide East Antarctica and West Antarctica. They include a number of separately named mountain groups, which are often again subdivided into smaller ranges.
The range was first sighted by James Clark Ross in 1841 at what was later named the Ross Ice Shelf in his honor. It was first crossed during the British National Antarctic Expedition of 1901-1904.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 Transantarctic Mountains and is covered by the West Antarctic Ice Sheet. It lies between the Ross Sea (partly covered by the Ross Ice Shelf), and the Weddell Sea (largely covered by the Filchner-Ronne Ice Shelf). It may be considered a giant peninsula stretching from the South Pole towards the tip of South America.
West Antarctica is largely covered by the Antarctic ice sheet, but there have been signs that climate change is having some effect and that this ice sheet may have started to shrink slightly. The coasts of the Antarctic Peninsula are the only parts of West Antarctica that become (in summer) ice-free. These constitute the Marielandia Antarctic tundra and have the warmest climate in Antarctica. The rocks are clad in mosses and lichens that can cope with the intense cold of winter and the short growing-season.