RAPID AND WIDESPREAD DISPERSAL OF FLOOD SEDIMENT ON THE NORTHERN CALIFORNIA MARGIN

The dispersal of flood sediment from small river systems is a poorly s tudied, yet potentially important aspect of active continental-margin sedimentation, In January 1995, during a flood with a 30 yr return per iod, the Eel River (northern California) delivered an estimated 25 +/- 3 x 10(6) t (metric tons) of fine-grained (<62 mu m) sediment to the ocean, The flood formed a distinct layer on the sea bed that was cente red on the 70 m isobath, extended for 30 km along shelf and 8 km acros s shelf, and was as thick as 8.5 cm, but contained only 6 x 10(6) t of sediment, Thus, 75% of the flood-derived sediment did not form a reco gnizable deposit, but was instead rapidly and widely dispersed over th e continental margin, Stratigraphic models of, and compilations of sed iment flux to, active continental margins need to take the dispersive nature of small river systems into account.