Mariana Trench

Coordinates: 11°21′N 142°12′E / 11.350°N 142.200°E / 11.350; 142.200 Coordinates: 11°21′N 142°12′E / 11.350°N 142.200°E / 11.350; 142.200 The Mariana Trench or Marianas Trench is located in the western Pacific Ocean about 200 kilometres (124 mi) east of the Mariana Islands, and has the deepest natural trench in the world. It is a crescent-shaped trough in the Earth's crust averaging about 2,550 km (1,580 mi) long and 69 km (43 mi) wide. The maximum known depth is 10,984 metres (36,037 ft) (± 25 metres ) at the southern end of a small slot-shaped valley in its floor known as the Challenger Deep. However, some unrepeated measurements place the deepest portion at 11,034 metres (36,201 ft). By comparison: if Mount Everest were placed into the trench at this point, its peak would still be over two kilometres (1.2 mi) under water. At the bottom of the trench the water column above exerts a pressure of 1,086 bars (15,750 psi), more than 1,000 times the standard atmospheric pressure at sea level. At this pressure, the density of water is increased by 4.96%, so that 95.27 of any unit of volume of water under the pressure of the Challenger Deep would contain the same mass as 100 of those units at the surface. The temperature at the bottom is 1 to 4 °C (34 to 39 °F). The trench is not the part of the seafloor closest to the center of the Earth. This is because the Earth is an oblate spheroid, not a perfect sphere; its radius is about 25 kilometres (16 mi) smaller at the poles than at the equator. As a result, parts of the Arctic Ocean seabed are at least 13 kilometres (8.1 mi) closer to the Earth's center than the Challenger Deep seafloor. In 2009, the Marianas Trench was established as a United States National Monument. Xenophyophores have been found in the trench by Scripps Institution of Oceanography researchers at a record depth of 10.6 kilometres (6.6 mi) below the sea surface. Data has also suggested that microbial life forms thrive within the trench. The Mariana Trench is named after the nearby Mariana Islands (in turn named Las Marianas in honor of Spanish Queen Mariana of Austria, widow of Philip IV of Spain). The islands are part of the island arc that is formed on an over-riding plate, called the Mariana Plate (also named for the islands), on the western side of the trench. The Mariana Trench is part of the Izu-Bonin-Mariana subduction system that forms the boundary between two tectonic plates. In this system, the western edge of one plate, the Pacific Plate, is subducted (i.e., thrust) beneath the smaller Mariana Plate that lies to the west. Crustal material at the western edge of the Pacific Plate is some of the oldest oceanic crust on earth (up to 170 million years old), and is therefore cooler and more dense; hence its great height difference relative to the higher-riding (and younger) Mariana Plate. The deepest area at the plate boundary is the Mariana Trench proper. The movement of the Pacific and Mariana plates is also indirectly responsible for the formation of the Mariana Islands. These volcanic islands are caused by flux melting of the upper mantle due to release of water that is trapped in minerals of the subducted portion of the Pacific Plate. The trench was first sounded during the Challenger expedition in 1875, using a weighted rope, which recorded a depth of 4,475 fathoms (8,184 metres; 26,850 feet). In 1877, a map was published called Tiefenkarte des Grossen Ozeans ('Deep map of the Great Ocean') by Petermann, which showed a Challenger Tief ('Challenger deep') at the location of that sounding. In 1899, USS Nero, a converted collier, recorded a depth of 5,269 fathoms (9,636 metres; 31,614 feet).