Just as we have craters on our land masses, oceans too have such trenches. Though there are bit difficult to be visited by most of us, Mariana Trench is a should know place because it is the deepest trench in oceans of the world. Mariana trench is located in the western Pacific Ocean, to the east of the Mariana Islands. Amazingly it is about 2,550 kilometres (1,580 mi) long but has a mean width of only 69 kilometres (43 mi). It reaches a maximum-known depth of about 10.91 kilometres (6.78 mi) at the Challenger Deep, a small slot-shaped valley in its floor, at its southern end; although some unrepeated measurements place the deepest portion at 11.03 kilometres (6.85 mi). If Mount Everest, the highest mountain on Earth at 8,850 metres (29,040 ft), was set in the deepest part of the Mariana Trench, there would be 2,060 metres (6,760 ft) of water left above it. So think how deep is that????
The Mariana for this trench is from the nearby islands; Mariana Islands. These islands were claimed by Spain and they established a colony there, and gave the islands the official title of Las Marianas in honor of Spanish Queen Mariana of Austria, widow of Philip IV of Spain. The Trench is part of the Izu-Bonin-Mariana Arc geological boundary system that forms the boundary between two tectonic plates. In this system, the western edge of one plate, the Pacific Plate, is subducted beneath the smaller Mariana Plate that lies to the west. 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 indirectly 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 1,086 bars (15,750 psi), over one thousand times the standard atmospheric pressure at sea level. Anyhow, this is not the closest place to the center of the Earth.
As many of us know, trenches in the world are used for the disposal of nuclear waste. Likewise, the Mariana Trench has been proposed as a site for nuclear waste disposal, in the hope that tectonic plate subduction occurring at the site might eventually push the nuclear waste deep into the Earth's mantle. But this is not legalized yet. Furthermore, plate subduction zones are associated with very large mega thrust earthquakes of which the effects on any specific site are unpredictable and possibly adverse to the safety of long-term disposal.
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