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

• Aleutian Trench
• Cayman Trench (max depth 7,686 m)
• Japan Trench (max depth 9,000 m)
• Kermadec Trench
• Kuril Trench
• Mariana Trench (max depth 10,924 m)
• Middle America Trench
• Peru-Chile Trench (max depth 8,065 m)
• Puerto Rico Trench
• Ryukyu Trench (Nansei-Shoto Trench)
• Sunda Trench
• Tonga Trench (max depth 10882 m)

See also

• Oceanic ridge
• plate tectonics
• physical oceanography
• list of landforms