The deepest known part of the oceans is the Challenger Deep located in the Mariana Trench east of the Philippines. It is approximately 11,034 meters (6,201 feet) below sea level, making it the lowest elevation on Earth. The trench was first surveyed in 1951 and the Challenger Deep within it was reached by a manned submersible in 1960. It is formed at a subduction zone where one tectonic plate slides under another.