Mariana Trench
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Location of the Mariana Trench

The Mariana Trench (or Mariana's Trench) is the deepest part of the world's oceans, and the deepest location on the surface of the Earth's crust. It has a maximum depth of about 11 km (6.8 mi), and is located in the western North Pacific Ocean, to the east and south of the Mariana Islands, near Guam.

The trench forms the boundary between two tectonic plates, where the Pacific Plate is subducted beneath the Philippine Plate. The bottom of the trench is farther below sea level than Mount Everest is above it (8,850m/29,035ft). At the bottom, the water column above exerts a pressure of 108.6 MPa, over one thousand times the standard atmospheric pressure at sea level.

Measurement and study

Cross-section of Mariana Trench, NOAA image

See also: Challenger Deep

The trench was first surveyed in 1951 by the Royal Navy vessel Challenger, which gave its name to the deepest part of the trench, the Challenger Deep.^[1] Using echo sounding, the Challenger II measured a depth of 5,960 fathoms (10,900 metres, 35,760 ft) at 11°19′N, 142°15′E.^[2]

In 1957, the Soviet vessel Vityaz reported a depth of 11,034 meters (36,200 ft), dubbed the Mariana Hollow.^[3] (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 (35,810 ft), using precision depth gauges. ^[4]

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).^[2][5]

Descents

January 23, 1960: Trieste just before the dive

The 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.^[1] Iron shot was used for ballast, with gasoline for buoyancy.^[1] The onboard systems indicated a depth of 11,521 meters (37,799 ft), but this was later revised to 10,916 meters (35,813 ft).^{citation needed} At the bottom, Walsh and Piccard were surprised to discover soles or flounder about 30 cm (1 ft) long,^[6] as well as shrimp.^{citation needed} According to Piccard, "The bottom appeared light and clear, a waste of firm diatomaceous ooze".^[6]

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).^[7]

The Woods Hole Oceanographic Institution is planning to send its Nereus hybrid remotely operated vehicle (HROV) to explore the trench in 2008.^[8]

References

See also

• Oceanic trench
• Izu-Ogasawara Trench
• Yap Trench

Coordinates: 11°21′N, 142°12′E