DESCRIPTION:
Indian Ocean Volcanoes and Volcanics

Andaman Islands Volcanoes
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The great sweep of the Sunda Arc, over 3,000 kilometers from NW Sumatra to the Banda Sea, results from the subduction of Indian Ocean crust beneath the Asian Plate. This arc includes 76 percent of the region's volcanoes, but those on either end are tectonically more complex. To the NNW, the basaltic volcanism of the Andaman Islands results from short spreading centers, and to the east the Banda Arc reflects Pacific Ocean crust subducted westward. North of this arc, tectonic complexity increases, with converging plate fragments forming multiple subduction zones, mainly oriented N-S, that in turn produce the Sulawesi-Sangihe volcanoes on the west and Halmahera on the east of the collision zone.

Andaman Islands Volcanoes, including Barren Island
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Barren Island, the only historically active volcano along a volcanic arc connecting Sumatra and Myanmar (Burma). The small 3-kilometer-wide island contains a 1.6-kilometer-wide crater partially filled by a cinder cone that has been the source of eruptions since the first was recorded in 1787. Lava flows reached the coast during several recent eruptions.

Major Western Indian Ocean Volcanoes
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The southernmost and largest of the two shield volcanoes forming Grand Comore Island, Karthala contains a 3 x 4 kilomters summit caldera generated by repeated collapse. Elongated rift zones extend to the NNW and SE from the summit of the Hawaiian-style shield, which has an asymmetrical profile that is steeper to the south. The lower SE rift zone forms the Massif du Badjini, a peninsula at the SE tip of the island. Historical eruptions have modified the morphology of the compound, irregular summit caldera. More than twenty eruptions have been recorded since the 19th century from both summit craters and flank vents; many lava flows have reached the sea. It has erupted at least 22 times since 1828, including September-October 1972.

Marion Island, South Africa's only historically active volcano, lies at the southwest end of a submarine plateau immediately south of the southwest Indian Ocean Ridge, opposite Prince Edward Island. The low profile of 24-kilometer-wide Marion Island is formed by two young shield volcanoes that rise above a flat-topped submarine platform. The 1230-meter-high island is dotted by about 150 cinder cones, smaller scoria cones, and coastal tuff cones. More than 130 scoria cones and many lava flows formed during the Holocene. Many of these appear younger than the 4,020 BP peat overlying one of the flows (Verwoerd and others, 1981). Young unvegetated lava flows appear to be only a few 100 years old (Verwoerd and Langenegger, 1967). A meteorological station is maintained there by the South African government.

This intriguing volcanic island is administered by South Africa and reflects the unique pattern of volcanism associated with the southern oceans. Marion consists of a system of radiating lava flows and faults, organized around a central summit region. This summit region is permanently ice and snow covered, and the island probably had a permanent ice cap during the more recent ice age. Hydromagmatic volcanic features can be observed in the coastal regions of this island, as well as numerous scoria cones. At present there are no trees on the island, but studies have suggested that a more diverse flora may have existed on the island in the recent past.

Africa Volcanoes and Volcanics Menu

Andaman Islands Volcanoes, including Barren Island
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Narcondum volcano, an island possession of India in the Andaman Sea, is part of a volcanic arc that continues northward from Sumatra to Burma (Myanmar). The small 3 x 4 kilometer-wide conical island, located about 130 kilometers east of North Andaman Island, rises to 710 meters, but its base lies an additional 1000 meters beneath the sea. The island is densely vegetated, bounded by cliffs on the southern side, and capped by three peaks. No evidence of historical volcanism is present, although the summit region is less densely vegetated. Volcanism at the andesitic volcano is considered to have continued into the Holocene (Krishnan 1957). The island's name means "pit of hell," although the name could have been mistakenly transferred from the historically active Barren Island volcano, 140 kilometers to the SSW.

Major Western Indian Ocean Volcanoes
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This region is a mixture of island hotspot volcanoes ... The Comoros Islands and Reunion dominate the eruption record ... Reunion was known to the Arabs and visited by the Portuguese in the early 1500s. The first of its known eruptions was in 1640, and France claimed the island around 1662. It has been French virtually continuously since then. Settlers moved in from 1715, and 600,000 people now live on the 2,510 square kilometer island. A modern volcano observatory was established there in 1980.

A basaltic shield volcano, Piton de la Fournaise (summit elevation 2,631 meters) forms the Southeast half of Reunion Island, 700 kilometers East of Madagascar. It has been one of the most active oceanic volcanoes, with more than 100 eruptions in the last 300 years. Three calderas formed at around 250,000, 65,000, and less than 5,000 years ago by progressive eastward slumping of the volcano. Most historical eruptions originated from the summit and flanks of a 400-meter-high lava shield that grew within the youngest caldera.

The massive Piton de la Fournaise shield volcano on the island of Reunion is one of the world's most active volcanoes. Much of its more than 530,000 year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the northwest. Three calderas formed at about 250,000, 65,000, and less than 5,000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of a 400-meter-high lava shield that has grown within the youngest caldera (Enclos Fouque´), which is 8 kilomters wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. Monitoring is done from the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF).

Piton de la Fournaise is an active basaltic shield volcano on the island of La Reunion in the Indian Ocean. It is similar in many respects to Kilauea Volcano, Hawaii, including its intraplate setting over a possible "hotspot" or melting anomaly in the uppper mantle. Piton de la Fournaise has grown by repeated extrusion of lava from the summit area and from fissures on all flanks of the volcano. The principle structural features of Fournaise are (1) a summit caldera and adjoining downfaulted trough, (2) a family of broadly curving faults that are nested around the caldera, and (3) three rift zones (Duffield and others, 1982). A few dikes are visible in the walls of the summit caldera, trending perpendicular to the walls (Upton and Wadsworth, 1970). Mouginis-Mark (1980) and Chevallier and Bachelery (1981) identify at least three periods of caldera collapse. Duffield and others (1982) recognize a similar sequence, with the added interpretation that each of the calderas has been breached by large landslides like those that occur on the south flank of Kilauea Volcano in Hawaii.

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