| Seal Nunataks | |
|---|---|
  Seal Nunataks | |
| Highest point | |
| Elevation | 368 m (1,207 ft)Murdoch Nunatak [1] |
| Coordinates | 65°07′30″S60°00′00″W / 65.12500°S 60.00000°W [2] |
| Geology | |
| Mountain type | volcanic vent |
The Seal Nunataks are a group of 16 islands called nunataks emerging from the Larsen Ice Shelf east of Graham Land, Antarctic Peninsula. The Seal Nunataks have been described as separate volcanic vents of ages ranging from Miocene to Pleistocene. There are unconfirmed reports of Holocene volcanic activity.
The Seal Nunataks are part of Graham Land and were embedded within the Larsen Ice Shelf [1] until its northern margin collapsed between 1986 and 1996, [3] rising from about 500 metres (1,600 ft) below sea level. [4] They were discovered by the Norwegian Carl Anton Larsen in December 1893, [1] who also identified them as volcanoes and named them Seal Islands. [5] The Argentina Base Aérea Teniente Benjamín Matienzo is located in the Seal Nunataks. [6]
The Seal Nunataks are part of a volcanic province in West Antarctica which extends over the Antarctic Peninsula, Marie Byrd Land and Ross Island. In the Antarctic Peninsula, Alexander Island, James Ross Island and the Seal Nunataks form this volcanic province. Alexander Island was active between 48 and 18 million years ago. [7] James Ross Island lies about 150 kilometres (93 mi) northeast of the Seal Nunataks. [4]
The Seal Nunataks volcanic group contains at least sixteen volcanic cones, [4] the largest of which is 368 metres (1,207 ft) high Murdoch Nunatak. [1] From north to south they are Lindenberg island, Larsen Nunatak, Evensen Nunatak, Dallmann and Murdoch Nunatak, Akerlundh, Bruce and Bull Nunatak, Donald, Pollux and Christensen Nunatak, Arctowski and Gray Nunatak, Oceana Nunatak, Hertha Nunatak and Castor Nunatak. [2] The nunataks are for the most part tuyas [8] consisting of ridges with lengths of less than 1 to 6 kilometres (0.62 to 3.73 mi) flanked with scree deposits and occasionally by primary volcanic features. [9] According to Otto Nordenskjöld in 1901-1903, Christensen Nunatak features a crater. [5] Castor, Christensen and Hertha are the only vents which show evidence of subaerial activity in form of lava flows; elsewhere the nunataks are constructed by hyaloclastite, pillow lavas [1] and dykes. [10] The volcanoes appear to align along northwest-striking lines. [4]
The Antarctic Peninsula was a site of subduction from about 200 million years ago until 4 million years ago, when a number of spreading ridges collided with the subduction zone starting from 50 million years ago at Alexander Island and caused it to cease. The volcanic arc became inactive; however volcanic activity continued in different form over the entire peninsula. [7] In the case of the Seal Nunataks, volcanism commenced immediately after subduction had ceased and was probably facilitated by the presence of fracture zones in the already subducted slab. [11] Alternatively, the development of a slab window may have aided in the onset of volcanism. [12] Small volumes of magma ascending would generate the dispersed volcanic fields, like Seal Nunataks. [13]
There is only little evidence of the basement at Robertson Island, where sediments of Cretaceous age crop out. [2] The tectonic structure in the area appears to be a rift bordered by Robertson Island in the south, the Larsen Rift. [14] Lineaments associated with the former subduction of oceanic fracture zones west of the Antarctic Peninsula may have played a role in establishing the alignments of the Seal Nunataks volcanoes. [15]
The Seal Nunataks consist of basalt, [2] basalt which contains clinopyroxene, olivine and plagioclase. [16] Andesite and basanite have been reported as well. [17] The rocks define numerous suites, both alkali basalt, subalkaline basalts and basaltic andesites are represented. [18] Xenoliths consisting of lherzolite and spinel have been found at Seal Nunataks. [1] Their geochemistry implies that the magmas are primitive mantle-derived melts which underwent only a little fractional crystallization. [19]
Potassium-argon dating has yielded ages between 4 million years ago and "recent" for the rocks in the volcanic field, but the reliability of the dates decreases the younger they are. Pillow lavas are usually about 1.5 million years old while subaerial activity occurred 700,000 years ago. [1] The youngest dates were obtained on Donald and Gray, the dates being less than 200,000 years ago. [4] Glacial erratics on some of the nunataks imply that they were covered with glaciers in the past. [20]
The discoverer Captain Larsen observed volcanic activity on Christensen Nunatak and Lindenberg Island, but the reliability of these reports is considered to be unclear. [1] Fumaroles have been observed on Christensen, Dallman and Murdoch, and eruptions were reported on the last two in 1982. [4] This activity consisted of the possible formation of lava flows and a pyroclastic cone, respectively. [21] However, some reported fumarolic activity may be due to solar evaporation of snow, and tephra layers were only found in moraines, implying that it might not have been genuine volcanic eruptions. [22]
The Ring of Fire is a tectonic belt of volcanoes and earthquakes.
Gaussberg is an extinct, 370-metre-high (1,210-foot) high volcanic cone in East Antarctica fronting on Davis Sea immediately west of Posadowsky Glacier. It is ice-free and conical in nature, having formed subglacially about 55,000 years ago. The current edifice is thought to be the remains of a once-larger mountain that has been reduced by glacial and subaerial erosion. The volcano has produced lamproite magmas, and is the youngest volcano to have produced such magmas on Earth.
Mount Hampton is a shield volcano with a circular ice-filled caldera. It is a twin volcano with Whitney Peak to the northwest and has erupted phonolite rocks. It is the northernmost of the volcanoes which comprise the Executive Committee Range in Marie Byrd Land, Antarctica and was active during the Miocene.
Mount Melbourne is a 2,733-metre-high (8,967 ft) ice-covered stratovolcano in Victoria Land, Antarctica, between Wood Bay and Terra Nova Bay. It is an elongated mountain with a summit caldera filled with ice with numerous parasitic vents; a volcanic field surrounds the edifice. Mount Melbourne has a volume of about 180 cubic kilometres (43 cu mi) and consists of tephra deposits and lava flows; tephra deposits are also found encased within ice and have been used to date the last eruption of Mount Melbourne to 1892 ± 30 years. The volcano is fumarolically active.
Mount Morning is a shield volcano at the foot of the Transantarctic Mountains in Victoria Land, Antarctica. It lies 100 kilometres (62 mi) from Ross Island. Mount Morning rises to an elevation of 2,723 metres (8,934 ft) and is almost entirely mantled with snow and ice. A 4.1 by 4.9 kilometres wide summit caldera lies at the top of the volcano and several ice-free ridges such as Hurricane Ridge and Riviera Ridge emanate from the summit. A number of parasitic vents mainly in the form of cinder cones dot the mountain.
Mount Takahe is a 3,460-metre-high (11,350 ft) snow-covered shield volcano in Marie Byrd Land, Antarctica, 200 kilometres (120 mi) from the Amundsen Sea. It is a c. 30-kilometre-wide (19 mi) mountain with parasitic vents and a caldera up to 8 kilometres (5 mi) wide. Most of the volcano is formed by trachytic lava flows, but hyaloclastite is also found. Snow, ice, and glaciers cover most of Mount Takahe. With a volume of 780 km3 (200 cu mi), it is a massive volcano; the parts of the edifice that are buried underneath the West Antarctic Ice Sheet are probably even larger. It is part of the West Antarctic Rift System along with eighteen other known volcanoes.
Mount Waesche is a mountain of volcanic origin at the southern end of the Executive Committee Range in Marie Byrd Land, Antarctica. It is 3,292 metres (10,801 ft) high, and stands 20 kilometres (12 mi) southwest of Mount Sidley, the highest volcano in Antarctica. The mountain lies southwest of the Chang Peak caldera and is largely covered with snow and glaciers, but there are rock exposures on the southern and southwestern slopes.
Bridgeman Island is one of the South Shetland Islands in Antarctica. It is an almost circular, volcanic island marked by steep sides, measuring 900 by 600 metres with a maximum elevation of 240 m (787 ft) high, lying 45 kilometres (28 mi) east of King George Island.
The Pleiades are a volcanic group in northern Victoria Land of Antarctica. It consists of youthful cones and domes with Mount Atlas/Mount Pleiones, a small stratovolcano formed by three overlapping cones, being the dominant volcano and rising 500 m (1,600 ft) above the Evans Névé plateau. Two other named cones are Alcyone Cone and Taygete Cone, the latter of which has been radiometrically dated to have erupted during the Holocene. A number of tephra layers across Antarctica have been attributed to eruptions of this volcanic group, including several that may have occurred within the last few hundred years.
Crary Mountains are a group of ice-covered volcanoes in Marie Byrd Land, Antarctica. They consist of two or three shield volcanoes, named Mount Rees, Mount Steere and Mount Frakes, which developed during the course of the Miocene and Pliocene and last erupted about 30,000-40,000 years ago. The first two volcanoes are both heavily incised by cirques, while Mount Frakes is better preserved and has a 4 kilometres (2.5 mi) wide caldera at its summit. Boyd Ridge is another part of the mountain range and lies southeast of Mount Frakes; it might be the emergent part of a platform that underlies the mountain range.
Volcanic activity is a major part of the geology of Canada and is characterized by many types of volcanic landform, including lava flows, volcanic plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes, and maars, along with less common volcanic forms such as tuyas and subglacial mounds.
The Canadian Cascade Arc, also called the Canadian Cascades, is the Canadian segment of the North American Cascade Volcanic Arc. Located entirely within the Canadian province of British Columbia, it extends from the Cascade Mountains in the south to the Coast Mountains in the north. Specifically, the southern end of the Canadian Cascades begin at the Canada–United States border. However, the specific boundaries of the northern end are not precisely known and the geology in this part of the volcanic arc is poorly understood. It is widely accepted by geologists that the Canadian Cascade Arc extends through the Pacific Ranges of the Coast Mountains. However, others have expressed concern that the volcanic arc possibly extends further north into the Kitimat Ranges, another subdivision of the Coast Mountains, and even as far north as Haida Gwaii.
Melville Peak is a prominent peak surmounting Cape Melville, the eastern cape of King George Island, in the South Shetland Islands off Antarctica. It represents an eroded stratovolcano of unknown age and contains a volcanic crater at its summit. A volcanic ash layer similar in composition to Melville Peak has been identified 30 km (19 mi) away from the volcano and may indicate Melville Peak has been volcanically active in the last few thousand years.
The Antarctic Peninsula, roughly 1,000 kilometres (650 mi) south of South America, is the northernmost portion of the continent of Antarctica. Like the associated Andes, the Antarctic Peninsula is an excellent example of ocean-continent collision resulting in subduction. The peninsula has experienced continuous subduction for over 200 million years, but changes in continental configurations during the amalgamation and breakup of continents have changed the orientation of the peninsula itself, as well as the underlying volcanic rocks associated with the subduction zone.
Argo Point is a scoria cone in Jason Peninsula, Antarctica, at a height of 360 metres (1,180 ft) above sea level. Associated with the Seal Nunataks, the cone has a diameter of 300 metres (980 ft) and its snow-filled crater has a gap on its northern side. The cone is constructed on a formation of lava and scoria over 175 metres (574 ft) thick, which may lie on Jurassic rocks. Glaciers or wind have eroded debris from the cone, forming a "tail" several kilometres long on the ice.
Fueguino is a volcanic field in Chile. The southernmost volcano in the Andes, it lies on Tierra del Fuego's Cook Island and also extends over nearby Londonderry Island. The field is formed by lava domes, pyroclastic cones, and a crater lake.
Mount Rittmann is a volcano in Antarctica. Discovered in 1988–1989 by an Italian expedition, it was named after the volcanologist Alfred Rittmann (1893–1980). It features a 2 kilometres (1.2 mi) or 8 by 5 kilometres wide caldera which crops out from underneath the Aviator Glacier. The volcano was active during the Pliocene and into the Holocene, including large explosive eruptions; a major eruption occurred in 1254 CE and deposited tephra over much of Antarctica. Currently, the volcano is classified as dormant.
The James Ross Island Volcanic Group is a stratigraphic unit of Cenozoic age distributed on James Ross Island and Vega Island of the James Ross Island group, the Tabarin and Trinity peninsulas of Graham Land and surrounding islands in the Prince Gustav and Antarctic sounds.
Mount Berlin is a glacier-covered volcano in Marie Byrd Land, Antarctica, 100 kilometres (62 mi) from the Amundsen Sea. It is a roughly 20-kilometre-wide (12 mi) mountain with parasitic vents that consists of two coalesced volcanoes: Berlin proper with the 2-kilometre-wide (1.2 mi) Berlin Crater and Merrem Peak with a 2.5-by-1-kilometre-wide crater, 3.5 kilometres (2.2 mi) away from Berlin. The summit of the volcano is 3,478 metres (11,411 ft) above sea level. It has a volume of 200 cubic kilometres (48 cu mi) and rises from the West Antarctic Ice Sheet. It is part of the Marie Byrd Land Volcanic Province. Trachyte is the dominant volcanic rock and occurs in the form of lava flows and pyroclastic rocks.
The Hudson Mountains are a mountain range in western Ellsworth Land just east of Pine Island Bay at the Walgreen Coast of the Amundsen Sea. They are of volcanic origin, consisting of low scattered mountains and nunataks that protrude through the West Antarctic Ice Sheet. The Hudson Mountains are bounded on the north by Cosgrove Ice Shelf and on the south by Pine Island Glacier. The mountains were volcanically active during the Miocene and Pliocene, but there is evidence for an eruption about two millennia ago and uncertain indications of activity in the 20th century.
| Authority control databases: Geographic |
|---|
