BERING CANYON

submarine canyon in the Bering Sea, 250 miles (400 km) long, and possibly the longest such feature in the world. The canyon head is situated at the edge of the continental shelf north of Umnak Island in the Aleutians. Its upper half is fed by a number of tributary valleys and trends southwestward. With depth, the canyon turns gradually northwestward, then turns abruptly to trend north along its lower 45 miles (72 km) to its mouth on the continental rise at a depth of 10,500 feet (3,200 m). The canyon is asymmetric in cross section; along its northerly trend its western wall is as steep as 13, and its eastern wall has slopes of only 2 to 3. Maximum relief is at least 2,600 feet (800 m), and the canyon's volume has been estimated at 1,030 cubic miles (4,300 cubic km), compared with volumes of less than 75 cubic miles for most other canyons. Bering Canyon is believed to have formed during late Tertiary and Pleistocene times, when large masses of sediment supplied by Alaskan and Siberian rivers slumped down the continental slope.