Abstract

An integrated process study of the relationship between debris flows and turbidity currents was carried out in the San Dimas Experimental Forest and adjoining reservoirs in the San Gabriel Mountains near Los Angeles. The initiation, movement, and dynamics of subaerial debris flows emanating from a series of experimentally burned watersheds, along with the subsequent movement of these flows subaqueously in two reservoirs, were studied using a network of instrumentation in addition to stratigraphy and mapping. Newly designed density sensors provided a continuous record of sediment concentration within the subaerial debris flows. These flows reached sediment concentrations of 60% by weight and velocities of 4-8 m s-1, and they involved total sediment volumes ranging from several hundred to several thousand cubic meters. In terms of processes within the reservoirs, the study documents the ability of the flows to move substantial distances as subaqueous debris flows, to convert to turbidity currents by means of subaqueous hydraulic jumps, and to then move along the reservoir floor as turbidity currents. The findings illustrate the ability of the hydraulic jumps to control the location of sediment deposition.

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