Antarctica :: Antarctica — The World Factbook - Central Intelligence Agency
Imagine flying in a plane over Antarctica, the southernmost continent and the kilometers ( million square miles), about half the size of the United States. Continuing a year tradition of mapping the continent at the bottom of the world To date, National Geographic has featured over 50 maps of Antarctica and the The colors, texturing, and perspective truly place the reader in the We opted for a line and slight tint boundary to give the extent of the sea. Geography:: Antarctica. Location: continent mostly south of the Antarctic Circle slightly less than times the size of the US. Land boundaries: . while no date indicates the country was an original treaty signatory; claimant nations are.
However, the occurrence of one unusually large earthquake of magnitude 6.
Ancient marine and lake basins were filled with a variety of sedimentary and volcanic debris eroded from primeval lands. During mountain-building episodes these materials were complexly deformed and recrystallized deep within the crust to form, particularly in East Antarctica, great crystalline-rock complexes.
Antarctica Fact File, What is it like in Antarctica, Antarctic environment 1
Again and again this cycle was repeated during the evolution of Antarctica. Mobility ceased approximately million years ago in the Transantarctic Mountains. Between that time, in the Devonian Period about million to million years agoand the Late Jurassic Epoch which began about million years agoa series of mainly quartzose quartz -containing sediments was laid down in ancient lakes and shallow seas in the sites of former mountain chains that had been carved away by erosion.
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- Pre-Quaternary Antarctic Peninsula Ice Sheet evolution
Known as the Beacon Sandstone, this formation of platform sediments contains a rich record of extinct Antarctic life-forms, including freshwater fish fossils in Devonian rocks; ancient temperate forestsof Glossopteris trees in coal deposits of Permian age about million to million years old and Dicroidium trees in Triassic-age coals those roughly million to million years old ; and large reptilessuch as Lystrosaurusand amphibians in Triassic rocks.
Tillites —rocks deposited by ancient glaciers —underlie Permian coal beds in numerous places in Antarctica just as they do in the other southern, including now tropical, continents. The widespread occurrence of glacial erraticscontaining microfossils of Cretaceous and Cenozoic age, is an indication of the presence of rocks that are younger than the Beacon Sandstone lying underneath ice sheets near the Transantarctic Mountains.
Relief There are two faces of the present-day continent of Antarctica. One, seen visually, consists of the exposed rock and ice-surface terrain. The other, seen only indirectly by seismic or other remote-sensing techniques, consists of the ice-buried bedrock surface. Both evolved through long and slow geologic processes. Effects of glacial erosion and deposition dominate everywhere in Antarctica, and erosional effects of running water are relatively minor.
Yet, on warm summer days, rare and short-lived streams of glacial meltwater do locally exist.SECRET CONTINENTS BEYOND ANTARCTICA
Glacially sculptured landforms now predominate, as they must have some million years ago, in an earlier period of continental glaciation of all of Gondwana.
Asiathe next, averages about 3, feet. The vast ice sheets of East Antarctica reach heights of 11, feet or more in four main centres: West Antarctica lies south of South America.
Antarctic Peninsula Ice Sheet evolution
The land in West Antarctica is lower than in the east, and in some places is even well below sea level. It is located on the coast and is 4, meters 16, feet tall. Under the surface of Antarctica, all is not cold and quiet. In fact, there is an active volcano in Antarctica: Mount Erebus, which is 3, meters 12, feet in height, is located in East Antarctica, on the edge of the Ross Ice Shelf—a place where ice extends far out over the ocean. Antarctica is also home to Lake Vostok, one of the world's largest lakes.
Antarctic Peninsula ice streams Palaeo-ice streams around the Antarctic Peninsula during and after the LGM, showing isochrones of recession. Reconstructing past palaeo ice streams provides an important context for understanding their recent behaviour, controls on this behaviour, and how ice streams might behave in the future.
Studying the basal characteristics of Antarctic palaeo ice streams means that the role of basal topography, bedrock geology and sediment erosion, transportation and deposition can be better understood. The diagnostic sediment-landform assemblages left behind by ice streams has meant that a large number of ice streams have been identified around the Antarctic continent, from both marine and terrestrial settings.
How We Made “The Melting of Antarctica”
At the Last Glacial Maximum, palaeo-ice streams extended to the shelf edge in West Antarctica and in the Antarctic Peninsula, but in East Antarctica they usually were restricted to the mid-outer shelf. These palaeo-ice streams occupied bathymetric troughs, and are identified by the glacial bedforms such as mega-scale glacial lineations in these troughs, and trough-mouth fans at their termini.
The outer-shelf zones of these cross-shelf troughs are characterised by soft, unconsolidated sediments, in which mega-scale glacial lineations and grounding zone wedges are preserved.
The inner shelf, instead, is generally composed of crystalline bedrock and has a higher bed roughness. Drumlins, grooved bedrock and meltwater channels are often observed here. Where there is detailed geomorphological data available, the retreat styles of various Antarctic ice streams can be better understood.
Three styles of retreat have been identified around the Antarctic Peninsula.
Antarctica - Wikipedia
Rapid retreat with floatation and calving results in well-preserved subglacial bedforms on the continental shelf. These include mega-scale glacial lineations. Marguerite Trough Ice stream is an example of an ice stream characterised by rapid recession. Episodic retreat is recorded by mega-scale glacial lineations that are overprinted by transverse grounding-zone wedges, each recording a pause in ice stream retreat with a stationary grounding line.
An example of this would be the ice stream that extended out of the Larsen A embayment on the Antarctic Peninsula. Finally, slow and steady retreat is recorded by numerous closely-spaced moraines and intermittent grounding-zone wedges. In the Western Ross Sea, there are six bathymetric troughs on the continental shelf. The palaeo-ice stream was about km long, with a zone of glacial deposition on the outer shelf, and erosional landforms on the inner shelf. Transverse sedimentary ridges overprint mega-scale glacial lineations throughout.
They are grounding zone wedges, and are m high, m to 8 km apart.
There are also smaller moraines, m high and m apart[47, 48]. The geomorphological record therefore suggests that retreat varies strongly between different troughs, with three principle styles of retreat recognised. This suggests that individual ice streams respond differently to external forcings during deglaciation, and instead are regulated by local factors, such as drainage basin size, bathymetry and sediment supply.
The western sector of the Ross Sea is fed from two drainage basins in East Antarctica measuring 1. This huge drainage basin may have meant that the outlet glaciers may have responded more slowly to external forcing. The Marguerite Bay drainage basin, in contrast, would have been of the order of 10, tokm2 during the LGM, and the ice streams draining this basin would have responded more rapidly to changes in external forcing.
Constraints such as these are important for numerical models that attempt to replicate and predict the past and future behaviour of the Antarctic Ice Sheet.
By analysing retreat styles and rates of retreat around Antarctica, we can put more recent variations into context and determine their significance.
The individual characteristics of each ice stream modulates its recession.