Oceanic trench

An oceanic trench is a long, narrow depression in the seafloor, usually formed where one tectonic plate bends and descends beneath another at a subduction zone.

Subduction: The descent of one tectonic plate beneath another into the mantle. A descending plate bends the seafloor into a trench at a convergent boundary.
Mariana Trench: A trench in the western Pacific that contains the deepest known point in the ocean. It is the best-known example of an exceptionally deep oceanic trench.
Megathrust earthquake: A large earthquake on the shallow boundary between a subducting plate and an overriding plate. Some of the largest earthquakes rupture the plate interface beneath trenches.
Mid-ocean ridge: A long underwater mountain chain where new oceanic crust forms as plates move apart. Ridges mark seafloor spreading, unlike trenches, where oceanic crust descends.
Convergent boundary: A tectonic plate boundary where two plates move toward one another. Oceanic trenches commonly mark convergent boundaries where a plate is being consumed.
Challenger Deep: The deepest known region of the ocean, located within the Mariana Trench. This basin lies at the trench’s greatest measured depths.
Tsunami: A series of long ocean waves caused by a large displacement of seawater. Sudden seafloor movement at a subduction zone can generate tsunamis.
Ocean basin: A broad, low-lying region of oceanic crust between continental margins and mid-ocean ridges. A trench is a narrow feature within the wider ocean basin.
Wadati–Benioff zone: A dipping zone of earthquakes that traces a descending tectonic plate within Earth. Its earthquake pattern follows the slab beneath a trench.
Peru–Chile Trench: A trench off western South America where the Nazca Plate subducts beneath the South American Plate. Its subduction system is associated with major earthquakes and the Andes.

Linked from 16 pages