An ocean trench is a long, narrow depression or deep valley on the seafloor, and it is the deepest part of the ocean. Ocean trenches are found in every ocean basin on the planet, although the deepest ocean trenches ring the Pacific as part of the so-called “Ring of Fire” that also includes active volcanoes and earthquake zones. They are typically 50 to 100 kilometers wide and 3 to 4 kilometers deep. Ocean trenches are a result of tectonic activity, which describes the movement of the Earth’s lithosphere. In particular, ocean trenches are a feature of convergent plate boundaries, where two or more tectonic plates meet. At many convergent plate boundaries, dense lithosphere melts or slides beneath less-dense lithosphere in a process called subduction, creating a trench.

The intense pressure, lack of sunlight, and frigid temperatures of the hadalpelagic zone make ocean trenches some of the most unique habitats on Earth. Despite the extreme depth, high pressure, and low light conditions, trenches are home to various specialized and often endemic species, which are specially adapted to survive in these challenging conditions. Oceanic trenches are important in geology and marine biology due to their significance in understanding Earth’s geological processes, supporting unique marine biodiversity, influencing ecological processes, providing insights into evolutionary studies, and potential resource exploration.