narrow submarine depression lying near the Equator in the mid- Atlantic Ocean and trending east-west between the shoulders of South America and Africa. Reaching a maximum depth of 25,453 feet (7,758 m), it represents one of the ocean's deepest soundings. The trench is 186 miles (300 km) long and has a mean width of 12 miles (19 km) and a total area of 2,317 square miles (6,000 square km).

The Romanche Gap is one of the few exceptionally deep trenches found in isolation from submarine mountain ranges or the edges of continental shelves. The Romanche Gap interrupts the north-south–trending mid-Atlantic Ridge; near its midpoint, transverse faults at intervals have relieved slowly accumulating stresses by allowing the rock of the ridge to slip along a line that runs generally east-west. Consequently, the Romanche Gap offsets the mid-Atlantic Ridge by more than 400 miles (640 km). The trench is covered by a debris of coarse, fragmented rocks resulting from gravitational sliding and slumping.