Archipelagic apron

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An archipelagic apron is a fan-shaped gently sloping region of sea floor found around oceanic islands, particularly in the south Pacific Ocean. The name was first proposed by Henry William Menard in 1956 because of the resemblance of the slope to an apron. While most such underwater sedimentary surfaces are generally smooth, some are rough in texture. The total volume occupied by an archipelagic apron is often many times that of the adjacent island. Hence, it is unlikely to have formed from sediments washed off the part of the island above sea level. [1] [2] Instead, archipelagic aprons most likely formed from debris avalanches and pyroclastic flows. The material is then reworked by turbidity currents to achieve their current form. Such aprons form about eight percent of the area of the Pacific basin. [3]

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<span class="mw-page-title-main">Henry William Menard</span> American geologist (1920–1986)

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The Mid-Pacific Mountains (MPM) is a large oceanic plateau located in the central North Pacific Ocean or south of the Hawaiian–Emperor seamount chain. Of volcanic origin and Mesozoic in age, it is located on the oldest part of the Pacific Plate and rises up to 2 km (1.2 mi) above the surrounding ocean floor and is covered with several layers of thick sedimentary sequences that differ from those of other plateaux in the North Pacific. About 50 seamounts are distributed over the MPM. Some of the highest points in the range are above sea level which include Wake Island and Marcus Island.

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Alexa Bank is a seamount in Samoa, northwest of Rotuma. The seamount reaches a depth of 18–21 metres (59–69 ft) below sea level and has the appearance of an atoll with a flat top and steep slopes. Some active coral growth takes place at its top, but if it ever was an active atoll it has now drowned. It was probably formed by the Samoa hotspot 24 million years ago, although older volcanism about 40 million years ago has also been identified.

Takuyo-Daisan is a guyot in the Western Pacific Ocean off Japan. It is 1,409 metres (4,623 ft) deep and has a square-shaped flat top surrounded by a perimeter ridge. Several other seamounts lie nearby.

<span class="mw-page-title-main">Horizon Guyot</span> Tablemount in the Pacific Ocean

Horizon Guyot is a presumably Cretaceous guyot (tablemount) in the Mid-Pacific Mountains, Pacific Ocean. It is an elongated ridge, over 300 kilometres (190 mi) long and 4.3 kilometres (2.7 mi) high, that stretches in a northeast–southwest direction and has two flat tops; it rises to a minimum depth of 1,443 metres (4,730 ft). The Mid-Pacific Mountains lie west of Hawaii and northeast of the Line Islands.

References

  1. Hill, M. N. (1963). The Earth Beneath the Sea. The Sea: Ideas and Observations on Progress in the Study of the Seas. Vol. 3. Harvard University Press. p. 336. ISBN   978-0-674-01730-6.
  2. Menard, Henry W. (1956). "Archipelagic Aprons". Bulletin of the American Association of Petroleum Geologists. 40. doi:10.1306/5CEAE56B-16BB-11D7-8645000102C1865D.
  3. Leyrit, Hervé; Montenat, Christian (2000). Volcaniclastic rocks, from magmas to sediments. CRC Press. p. 27. ISBN   978-90-5699-278-1.