The oceanic trenches are several hundred kilometres long but narrow topographic depressions of the sea floor. They also are the deepest parts of the ocean floor. A trench marks the position at which the flexed, subducting slab begins to go under, on the convex side and between 50 and 250 km from a volcanic arc. Oceanic trenches typically extend 3 to 4km (1.9-2.5 mi) below the level of the surrounding oceanic floor. The deepest ocean depth to be sounded is in the Challenger Deep of the Mariana Trench at a depth of 10,991m (35,798 ft) below sea level.
Major oceanic trenches
Last updated: 09-12-2005 02:39:13