submarine trench in the eastern Pacific Ocean, about 100 miles (160 km) off the coast of Peru and Chile. It reaches a maximum depth of 26,460 feet (8,065 m) below sea level in Richards Deep and is approximately 3,666 miles (5,900 km) long; its mean width is 40 miles (64 km) and it covers an expanse of some 228,000 square miles (590,000 square km).

The Peru-Chile Trench marks the subduction of the Nazca Plate under the South American Plate and lies offshore from an area of active volcanism. The trench sediments are alternate layers of turbidites and oceanic deposits, mainly clays, volcanic ash, and siliceous oozes, with some carbonates and, possibly, primary dolomites. Studies of these sediments indicate the presence of metals initially disseminated in newly erupted underwater volcanic rocks.