submarine depression in the Pacific Ocean off the western coast of Central America. Extending northwest-southeast for more than 1,700 miles (2,750 km) from central Mexico to Costa Rica, the trench reaches a maximum depth of 21,880 feet (6,669 metres) and covers a total area of 37,000 square miles (96,000 square km). The shallower northern section of the trench tends to curve along the coast of Mexico, paralleling the break in the continental shelf, while the deeper southern section follows a more linear course. The southern section of the trench is usually associated with active volcanism on land, as, for example, the eruption in 1982 of El Chichón volcano in southern Mexico; the trench floor in this area is irregular.