Mariana Trench or Marianas Trench,mâr˝ēăn´əz [key], elongated depression on the Pacific Ocean floor, 210 mi (338 km) SW of Guam. It is the deepest known depression on the earth's surface, having been measured by various means since the 1950s at 35,760–36,201 ft (10,900–11,034 m) below sea level at Challenger Deep, with a 2010 measurement by the U.S. Center for Coastal and Ocean Mapping at 36,070 ft (10,994 m). The Trieste, a U.S. navy bathyscape crewed by Swiss oceanographyer Jacques Piccard and U.S. Navy Lieutenant Donald Walsh, reached its bottom in 1960. In 2012 James Cameron became the third person to descend to the Deep, in the submersible Deepsea Challenger. Victor Vescovo made the dive in 2019 in the submersible DSV Limiting Factor. Robotic vessels have also surveyed the trench and deep. The
Mariana Trench Marine National Monument, 96,714 sq mi (250,488 sq km), was established in 2009 to protect the submerged lands and waters around the trench and around the three northernmost Mariana Islands and 21 sites with undersea mud volcanoes and hydrothermal vents.
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