submarine depression forming the floor of the southwestern section of the Bering Sea in the Pacific Ocean. On the west it rises to meet Siberia and the Kamchatka Peninsula; on the northeast, the continental shelf of North America off southwestern Alaska; and on the south, the Aleutian Islands. The basin extends about 1,100 miles (1,800 km) north-south and 600 miles (1,000 km) east-west and is over 9,800 feet (3,000 m) deep. Its floor has a thick basaltic crust. The volcanic Aleutian Arc separates the basin from the floor of the North Pacific Ocean.