Английская Википедия:Bristol Island

Материал из Онлайн справочника
Перейти к навигацииПерейти к поиску

Шаблон:Short description Шаблон:Use dmy dates Шаблон:Infobox islands

Bristol Island is an uninhabited island in the South Sandwich Islands. The island is almost entirely surrounded by ice cliffs and largely covered with ice. It features both the oldest rocks of this archipelago and an active volcano that last erupted in 2016.

Geography and geomorphology

Bristol Island is one of the South Sandwich Islands, which lie southeast of South GeorgiaШаблон:Sfn in the Southern OceanШаблон:Sfn and extend over a distance of Шаблон:Convert in a north–south direction.Шаблон:Sfn It lies about Шаблон:Convert southwest of Montagu IslandШаблон:Sfn and is separated from Southern Thule by Forsters Passage.Шаблон:Sfn The first island of the South Sandwich Islands to be discovered was Freezland Rock, which was sighted on 31 January 1775 by a sailor named Freezland on James Cook's HMS Resolution. Cook considered Bristol Island to be a promontory on a larger island;Шаблон:Sfn it was Thaddeus von Bellingshausen who in 1819 determined that Bristol was actually an island.Шаблон:Sfn The island is almost inaccessible and thus among the most poorly studied of the South Sandwich Islands.Шаблон:Sfn

Bristol Island has dimensions of Шаблон:Convert,Шаблон:Sfn making it one of the largest in the South Sandwich Islands.Шаблон:Sfn It is roughly the shape of a square and almost entirely covered in ice. The points of the square are formed by the northern Fryer Point, the eastern Trulla Bluff, the southern Harker Point and the western Turmoil Point.Шаблон:Sfn In some places the coast is formed by sandy or bouldery beaches, but most of Bristol Island is surrounded by ice cliffs. They reach heights of Шаблон:ConvertШаблон:Sfn and emanate from an interior that features several ridges and peaks.Шаблон:Sfn Bristol Island has three mountains in its interior, the western Mount Sourabaya close to the centre of the island, the southern Mount Darnley and the eastern Havfruen Peak,Шаблон:Sfn which together form a horseshoe.Шаблон:Sfn Of these Mount Darnley is the highest point of Bristol Island, reaching an elevation of Шаблон:Convert above sea level.Шаблон:Sfn Mount Sourabaya reaches Шаблон:Convert; Havfruen Peak is Шаблон:ConvertШаблон:Sfn or Шаблон:Convert highШаблон:Sfn and may be a lava dome or a parasitic vent.Шаблон:Sfn Pyroclastic cones and three overlapping vents form Mount Sourabaya, the active centre of Bristol Island.Шаблон:Sfn

Several small islets occur all around Bristol Island. The largest ones (more than Шаблон:Cvt) lie all west of Turmoil Point and consist of Grindle Rock, Wilson Rock and Freezland Rock.Шаблон:Sfn These islets and numerous sea stacks formed through coastal erosion.Шаблон:Sfn The submarine portion of Bristol Island has an irregular shape, especially in the north and west where it extends to some distance from the coastline.Шаблон:Sfn A shallow shelf of less than Шаблон:Convert depth surrounds the island especially in the west, where it forms Freezland Bank. Towards the seafloor, Bristol Island widens to a diameter of Шаблон:Convert.Шаблон:Sfn Numerous submarine sector collapse scars surround the island especially on its southern side, while a ridge and a secondary seamountШаблон:Sfn and secondary volcanism lie due west and extend Шаблон:Convert from Bristol.Шаблон:Sfn

Geology

East of the South Sandwich Islands, the South America Plate subducts beneath the Scotia Plate at a rate of Шаблон:Convert. The subduction is responsible for the existence of the South Sandwich island arc, which is constituted by about eleven islandsШаблон:Sfn in an eastward curving chain,Шаблон:Sfn and submarine volcanoes including Protector in the north and Adventure and Kemp in the south.Шаблон:Sfn From north to south, the islands are Zavodovski Island, Leskov Island, Visokoi Island, Candlemas Island–Vindication Island, Saunders Island, Montagu Island, Bristol Island–Freezland Rock, Bellingshausen Island, and Cook Island–Thule Island. Most of the islands are stratovolcanoes of various sizes.Шаблон:Sfn

Composition

The principal volcanic rock of Bristol Island is basalt. Freezland Rock consists of andesiteШаблон:Sfn which – unlike the potassium-poor tholeiites of the main islandШаблон:Sfn – defines a calc-alkaline suite. Phenocrysts in both series include augite, hypersthene, olivine and plagioclase.Шаблон:Sfn Tyrrel suspected that schists found encased in an iceberg may come from Bristol Island.Шаблон:Sfn Isotope ratios of hafnium imply that the magma was formed with involvement of subducted pelagic sediments.Шаблон:Sfn

Eruption history

The oldest rock in the South Sandwich Islands is found at Bristol Island:Шаблон:Sfn A sample from Freezland Rock has yielded an age of 3.1±0.1 million years by potassium-argon dating.Шаблон:Sfn It, the rocks at Turmoil Point and the stacks between them may be part of an older, now eroded volcanoШаблон:Sfn made up by alternating dykes, lava flows and tuffs.Шаблон:Sfn The bulk of Bristol Island was probably built by emissions from the Sourabaya, Darnley and Havfruen centres and includes lava flows that form some of the capes,Шаблон:Sfn although bathymetric data imply that it mostly pre-dates the Freezland Rock volcano.Шаблон:Sfn

Recorded activity at Bristol goes back 150 years.Шаблон:Sfn Eruptions have been observed in 1823, 1935-1936, 1950 and 1956,Шаблон:Sfn and traces of very recent eruptions in 1964. A steaming crater was reported in 1962Шаблон:Sfn which is presently buried under snow and ice.Шаблон:Sfn The eruptions produced scoria conesШаблон:Sfn and reached volcanic explosivity indexes of 2-3.Шаблон:Sfn Historical eruptions have been centered on Mount SourabayaШаблон:Sfn and a crater on the western flank.Шаблон:Sfn The activity on Bristol Island led the Argentines in 1956 to abandon the refuge hut they had installed on Thule Island farther south,Шаблон:Sfn causing them to drop their plan to establish a permanent base there.Шаблон:Sfn A sulfate anomaly in the EPICA ice core from Dronning Maud Land, Antarctica, has been attributed to the 1956 eruption.Шаблон:Sfn Tephra layers in the East Antarctic Ice SheetШаблон:Sfn - such as in an ice core from Siple Dome - may come from the 1935 eruptionШаблон:Sfn although an origin at Cerro Azul in Chile is also possible.Шаблон:Sfn

In 2005, three overlapping craters cropped out from the ice at Mount Sourabaya, with another crater Шаблон:Convert farther east.Шаблон:Sfn During April-July 2016, an eruption at Mount Sourabaya emplaced two lava flows and produced ash emissions that were visible from satellitesШаблон:Sfn and led to the issuance of volcanic ash advisories.Шаблон:Sfn Temperature anomalies indicative of fumaroles are visible from satellitesШаблон:Sfn and are centered on the crater of Mount Sourabaya.Шаблон:Sfn Helicopter-assisted ascents to the summit of Mount Sourabaya have found hot ground.Шаблон:Sfn Ice is melted in the proximity of active cratersШаблон:Sfn but otherwise volcanic impacts on the ice cover are minimal.Шаблон:Sfn

Ecology

Algae and lichens grow where there is exposed rock,Шаблон:Sfn but unlike on many other South Sandwich Islands no vegetation is associated with volcanically heated ground.Шаблон:Sfn Bryophytes including mosses have been recovered from Freezland Rock. Penguins form colonies on Bristol Island, including one with thousands of individuals on Freezland Rock,Шаблон:Sfn and seabirds like Antarctic fulmarsШаблон:Sfn and imperial shags also breed on Bristol,Шаблон:Sfn although their populations are smaller here than on the other South Sandwich IslandsШаблон:Sfn and they may be impacted by volcanic activity.Шаблон:Sfn Penguin colonies are concentrated on headlands where the island is not ice covered.Шаблон:Sfn Isopods occur in supralittoral pools.Шаблон:Sfn Bryozoans have been recovered from shallow waters around Bristol.Шаблон:Sfn

See also

References

Шаблон:Reflist

Sources

Шаблон:Refbegin

Шаблон:Refend

External links

Шаблон:SGSSI

Партнерские ресурсы
Криптовалюты
Магазины
Хостинг
Разное

Источник — http://wikihandbk.com/ruwiki/index.php?title=Английская_Википедия:Bristol_Island&oldid=13641411