Modern sediment dispersal and accumulation in Quinault submarine canyon — A summary

Quinault Canyon, off the coast of Washington, intersects the dispersal path of modern Columbia River sediments on the continental shelf. Study of the dynamics, dispersal, and accumulation of these deposits in the canyon indicates that no systematic down-canyon transport occurs. Rather, sediment dispersal is controlled primarily by the regional flow pattern. Suspended particulate matter is resuspended on the shelf, primarily during winter storm events, and advected northward as a bottom nepheloid layer (BNL) over the shelf. Cross-canyon advection produces an intermediate nepheloid layer (INL) over the upper slope and canyon from which the suspended particulate matter settles rapidly, probably in amorphous aggregates. Rapid short-term deposition ( ∼ 10 −1 g cm −2 yr −1 ) and enhanced modern accumulation (generally 10 × 10 −2 g cm −2 yr −1 ) are confined to the upper canyon (1600 m), where fluctuations in deposition rates and grain size are related to specific shelf sediment resuspension events. In the lower canyon (1600 m), accumulation is slow and temporally uniform.