Sunday 17 July 2011

New Submarine Volcanoes discovered in the South Sandwich Islands.

The South Sandwich Islands are a group of volcanic islands in the southern ocean. The most northerly island, Zavodovski, is 560 km southeast of South Georgia. The most southerly, Thule (sometimes called Morrell), is 240 km further south, and 1200 km north of Antarctica.

They are a Volcanic Island Arc, made up of volcanoes on South Sandwich Microplate, a small tectonic plate between the South American, Scotia and Antarctic Plates. The South American Plate is being subducted beneath the South Sandwich Plate, as this happens rocks from the plate are drawn into the mantle of the Earth, where they are melted by heat from the Earth's core. Lighter material then rises up through the overlying South Sandwich Plate, where it is extruded at the surface, forming basalt volcanoes.

The South Sandwich Plate.

There are a number of previously recorded volcanoes in the South Sandwich Islands.

Protector Shoal is a submarine volcano 56 km northwest of Zavodovski Island; its highest point is 27 m bellow sea level in an area where the sea floor is an average of 1200 m deep. Protector Shoal last erupted in 1962.

Mount Curry is on Zavodovski Island and rises 551 m above sea level. Its last recorded eruption was in about 1819, but it has probably erupted since then - due to its remote location it has not been monitored closely due to its remote location (the 1819 eruption was only detected by new lava flows), it is suspected that there were eruptions in 1823, 1830 and 1908. With modern seismic monitoring and satellite technology any future eruptions are likely to be recorded.

Zavodovski Island.

Leskov island is 51 km to the southeast of Zavadovski Island, and the easternmost of the South Sandwich Islands. It reaches 190 m above sea level, and has a semicircular shape, being part of the rim of a collapsed volcanic caldera. The island is made up of andersitic lava, rather than basaltic as is found on the majority of the islands.

Mount Hodson is located on Visokoi Island, 56 km to the east of Leskov Island and 47 km southeast of Zavodski Island. The volcano rises 1005 m above sea level ('visokoi' means 'high' in Russian). Plumes were seen above the volcano in 1830 and 1930.

Candlemas Island is 43 km southeast of Visokoi Island, and is the cone of another submerged volcano. It has not been seen erupting since its discovery in 1755, though there were reports of steam issuing from the summit in 1823 and 1911, and some of the lava flows on the north flank may have formed within the last couple of hundred years.

3.2 km southwest of Candlemas Island, across the Nelson Channel, is Vindication Island, another volcano, though one that has not been extinct for at least 10 000 years. Its highest point is 430 m above sea-level.

Mount Michael is located on Saunders Island is 73 km south-southeast of Candlemas Island. It rises 990 m above sea-level and has a 700 m wide caldera. In 2001 Tom Lachlan-Cope, John Smellie and Russ Ladkin of the British Antarctic Survey published a paper in the Journal of Volcanology and Geothermal Research in which they described the discovery of an intermittent lava lake in the caldera of Mount Michael, using images from the Advanced Very High Resolution Radiometer, a set of sensors mounted on the Polar Operational Environmental Satellites, which are operated by the US National Oceanic and Atmospheric Administration.

Mount Belinda is located on Montagu Island, the largest of the South Sandwich Islands, 62 km south of Saunders Island. It has been more-or-less constantly active since 2001, when satellite images became available, and has probably been erupting since some time in the 1990s. Mount Belinda is a shield volcano (a volcano made from successive lava flows, giving it a lower profile than the more cone-shaped stratovolcanoes, which are formed from a combination of lava and ash deposits) which reaches 1371 m above sea-level, and has a caldera 6 km in diameter. On the southeastern point of Montagu Island lies Mount Oceanite, an ice covered extinct volcano, reaching 915 m above sea-level.

Satellite image of Montagu Island, showing smoke issuing from the summit of Mount Belinda in the centre of the picture and Mount Oceanite in the bottom right-hand corner.

Mount Darnley is located on Bristol Island, 60 km southwest of Montagu Island. It last erupted in 1956, and was previously recorded as having erupted in 1950, 1936, 1935 and 1823. The peak of the mountain is 1100 m above the sea.

Bellingshausen Island is 50 km southwest of Bristol Island. It is a stratovolcano with a summit 253 m above the sea and a crater 500 m wide. Smoke was seen issuing from Bellingshausen in 1930, 1962 and 1964, and an explosive crater was formed on the island some time between 1964 and 1986.

Mount Larson is located on Thule Island, 8 km west of Bellingshausen Island. It stands 710 m above sea level and has a lake in its crater which is kept from freezing by geothermal heat. Steam was seen coming from the crater in 1962, and fresh ash reported on the flank of the volcano.

Between Bellingshausen and Thule Islands is Cook Island, the only island in the South Sandwich group without a volcano. It is thought that Cook Island was once part of the same island as Thule, and there may be a submerged crater between the two.

40 km southwest of Thule Island is Vysokaya Bank, a suspected submarine volcano.

This month (July 2011) scientists lead by Dr Phil Leat from the British Antarctic Survey revealed the discovery of 12 submarine volcanoes in the South Sandwich Islands. The discoveries were made on two tours by the RSS James Clark Ross, using sonar mapping discovery, and were unveiled at the International Symposium on Antarctic Earth Sciences in Edinburgh this month. Some of the new volcanoes have been described as similar in size to Mount Fuji in Japan, rising from a sea-floor 3000 m deep to within 70 m of the surface.

Undersea volcanoes around Saunders Island.

A 3D image of the whole South Sandwich Islands group.

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