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					Mariana Trench
11°21′N 142°12′E / 11.35°N 142.2°E The Mariana Trench (or Marianas Trench) is the deepest known part of the world's oceans, and the lowest elevation of the surface of the Earth's crust. It is located in the western Pacific Ocean, to the east of the Mariana Islands. The trench is about 2,550 kilometres (1,580 mi) long but has a mean width of only 69 kilometres (43 mi). It reaches a maximum depth of about 11,034 metres (36,200 ft) at the Challenger Deep, a small slot-shaped valley in its floor, at its southern end.[1] Part of the Izu-Bonin-Mariana Arc system, the trench forms the boundary between two tectonic plates, where the western edge of the Pacific Plate is subducted beneath the small Mariana Plate. Because the Pacific plate is the largest of all the tectonic plates on Earth, crustal material at its western edge has had a long time since formation (up to 170 million years) to compact and become very dense; hence its great height-difference (which translates to water depth) relative to the higher-riding Mariana Plate, at the point where the Pacific Plate crust is subducted (is forced down beneath the other). This deep area is the Mariana trench proper. The movement of these plates is also responsible for the formation of the Mariana Islands. At the bottom of the trench, where the plates meet, the water column above exerts a pressure of 108.6 megapascals (15,750 psi), over one thousand times the standard atmospheric pressure at sea level. Some creatures of the type normally encountered that could live at these depths are few, but some fish species, like the angler fish or other deep-sea fish, have been spotted in these waters.[citation needed] If Mount Everest, the highest mountain on Earth at 8,848 metres (29,030 ft), was set in the deepest part of the Mariana Trench, there would be 2,076 metres (6,810 ft) of water left above it.[2]

Measurement and study

The Pacific plate is subducted below the Mariana Plate, creating the Mariana trench, and (further on) the arc of the Mariana islands, as water trapped in the plate is released and explodes upward to form island volcanoes.

See also: Challenger Deep The trench was first sounded during the Challenger expedition (December 1872 – May 1876), which recorded a depth of 9,636 m (31,614 feet). Challenger II surveyed the trench using echo sounding, a much more precise and vastly easier way to measure depth than the sounding equipment and drag lines used in the original expedition. During this survey, the deepest part of the trench was recorded when the Challenger II measured a depth of 5,960 fathoms (10,900 metres, 35,760 ft) at 11°19′N 142°15′E / 11.317°N 142.25°E,[3] known as the Challenger Deep.[2] In 1957, the Soviet vessel Vityaz reported a depth of 11,034 meters (36,200 ft), dubbed the Mariana Hollow.[4] (Although this claim was made by the Soviets in 1957, the finding has not been repeated by subsequent mapping expeditions using more accurate and modern equipment.)[citation needed] In 1962, the surface ship M.V. Spencer F. Baird recorded a maximum depth of 10,915 meters (35,840 ft), using precision depth gauges.[3] In 1984, the Japanese sent the Takuyō (拓洋), a highly specialized survey vessel, to the Mariana Trench and collected data using a narrow, multi-beam echo sounder; they reported a maximum depth of 10,924 meters, also reported as 10,920 meters ± 10 meters.[3][5] The most accurate measurement on record was taken by a Japanese probe, Kaikō (かいこう), which descended unmanned to the bottom of the trench on March 24, 1995 and recorded a depth of 10,911 meters (35,798 ft).[1] In 2003, a spot was found along the Mariana Trench, the depth of which is around the same depth as the Challenger Deep, possibly even deeper. It was discovered while scientists from the Hawaii Institute of Geophysics and Planetology were completing a survey around Guam; they used a sonar mapping system towed behind the research ship to conduct the survey. This new spot was named the HMRG (Hawaii Mapping Research Group) Deep, after the group of scientists who discovered it.[6]

Descents
January 23, 1960: Trieste just before the dive The Swiss-designed, Italian-built, United States Navy bathyscaphe Trieste reached the bottom at 1:06 p.m. on January 23, 1960, with U.S. Navy Lieutenant Don Walsh and Jacques Piccard on board.[2] Iron shot was used for ballast, with gasoline for buoyancy.[2] The onboard systems indicated a depth of 11,521 meters (37,799 ft), but this was later revised to 10,924 meters(35,840 ft).[1] At the bottom, Walsh and Piccard were surprised to discover soles or flounder about 30 cm (1 ft) long,[7] as well as shrimp.[citation needed] According to Piccard, "The bottom appeared light and clear, a waste of firm diatomaceous ooze".[7] The Woods Hole Oceanographic Institution sent its Nereus hybrid remotely operated vehicle (HROV) to explore the trench on May 31, 2009.[8]


				
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