The Columbia Encyclopedia, Sixth Edition. 2001-07.
Marianas trench
Marianas trough, or Marianas deep (mâr´´n´z) (KEY) , elongated depression on the Pacific Ocean floor, 210 mi (338 km) SW of Guam. It is the deepest (35,798.6 ft/10,911.5 m at the Challenger Deep) known depression on the earths surface. A U.S. navy bathyscape reached its bottom in 1960; a 1995 Japanese probe made what is probably the most accurate measurement of its depth.