Ocean Basin

Trenches are long, narrow, canyon-like structures, most often found adjacent to a continental margin. They occur much more commonly in the Pacific than in any of the other oceans. The deepest trench on Earth is the Marianas trench, which runs from the coast of Japan south and then west toward the Philippine Islands. Its deepest spot is 36,152 ft (11,022 m) below sea level and it runs a distance of about 1,580 mi (2,550 km). The longest trench is located along the coast of Peru and Chile. Its total length is 3,700 mi (5,900 km) and it has a maximum depth of 26,420 ft (8,055 m).

Earthquakes and volcanic activity are commonly associated with trenches. In fact, the trenches that encircle the Pacific Ocean are sometimes called the Ring of Fire because of the volcanic activity located there. According to the plate tectonic theory, trenches form at sites where one lithospheric plate is forced beneath another, or subducted, as a result of seafloor spreading elsewhere. Friction between the two plates is responsible for the associated earthquakes and volcanic activity.