deep-sea trench

deep-sea trench

 or oceanic trench

Any long, narrow, steep-sided depression in the ocean bottom in which maximum oceanic depths (24,000–36,000 ft, or 7,000–11,000 m) occur. The deepest known depression of this kind is the Mariana Trench. Most trenches occur at subduction zones, where one tectonic plate is thrust under another.

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deep-sea trench [¦dēp ¦sē ′trench]

(geology)

A long, narrow depression of the deep-sea floor having steep sides and containing the greatest ocean depths; formed by depression, to several kilometers' depth, of the high-velocity crustal layer and the mantle.