ASTORIA CANYON

submarine canyon and fan-valley system of the Pacific continental margin, off the coast of Oregon, U.S. The canyon's head is in water about 330 feet (100 m) deep, 11 miles (18 km) west of the mouth of the Columbia River. The canyon crosses the seaward half of the continental shelf in a westerly direction and trends sinuously down to the base of the continental slope and the apex of Astoria Fan at a depth of 6,840 feet (2,085 m), at which point it passes into Astoria Seachannel, a fan valley. The canyon is approximately 75 miles (121 km) long. Along its upper reaches it has a U-shaped cross section; however, it is V-shaped near the shelf break, where the canyon has its maximum relief of 3,000 feet (900 m). It varies in width from 1.5 to 8.3 miles (2.4 to 13.3 km). The canyon is entered by 13 tributaries. It is believed to have been cut by the movement of Columbia River sediment down to the Astoria Fan. The sediment is distributed over the fan through Astoria Seachannel, a fan valley of low relief at least 70 miles (113 km) long, with several distributaries. Astoria Seachannel, like other fan valleys, probably migrates laterally over the fan through time; its present position is the eastern portion of the fan, and its trend is southerly.