marginal trench

A deep-sea trench is a long, narrow, and steep-sided depression on the ocean floor, typically found where one tectonic plate subducts beneath another. These trenches can reach extreme depths, from approximately 7,300 to over 11,000 meters (24,000 to 36,000 feet). The deepest known is the Mariana Trench.1

Trenches form in subduction zones, where an oceanic plate sinks into the Earth's mantle. This process creates a V-shaped depression. Trenches are often associated with island arcs or continental mountain ranges. The Peru-Chile Trench is the longest, stretching about 5,900 km (3,700 miles). Most of the world's trenches are located in the Pacific Ocean.12