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Location of the Mariana Trench
The Mariana 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 11,033 metres (36,198 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 relative to the higher-riding Mariana Plate, at the point where the Pacific Plate crust is subducted. 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. If
Mount Everest, the highest mountain on Earth at 8,848 metres (29,029 ft), were set in the deepest part of the Mariana Trench, there would be 2,076 metres (6,811 ft) of water left above it.
[1]Because the Earth is not a perfect sphere, the trench is not the part of the seafloor closest to the
center of the Earth - parts of the
Arctic Ocean seabed are at least 13,000 meters closer to the center than the Challenger Deep seafloor.
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.
The trench was first sounded during the
Challenger expedition (December 1872 – May 1876), which recorded a depth of 9,636 m (31,614 feet).
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 (35,840 ft), using precision depth gauges.
[2]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 metres, also reported as 10,920 metres ± 10 metres.
[2][4]On 1 June 2009 sonar mapping of the Challenger Deep by the Simrad EM120 sonar multibeam bathymetry system for deep water (300 - 11.000 meters) mapping aboard the
RV Kilo Moana (mothership of the Nereus vehicle), has indicated a spot with a depth of 10,971 m (35,994 ft). The sonar system uses phase and amplitude bottom detection, with an accuracy of better than 0.2% of water depth across the entire swath (implying the depth figure is accurate to less than ± 11 meters).
[5][6]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.
[7]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.
[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 (35,814 ft).
[8] At the bottom, Walsh and Piccard were surprised to discover
soles or
flounder about 30 cm (1 ft) long,
[9] as well as a
shrimp.
[1] According to Piccard, "The bottom appeared light and clear, a waste of firm
diatomaceous ooze".
[9]Only three descents have ever been achieved. The first was the manned descent by
Trieste in 1960. This was followed by the unmanned
ROVs Kaikō in 1995 and
Nereus in 2009. These three expeditions directly measured very similar depths of 10,902 to 10,916 meters.
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