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Observations of the sediment and micro-relief found in submarine canyons from the Trieste I and II, Cousteau's diving saucer, and by SCUBA diving indicate that submarine erosional processes are actively modifying the shape of many canyons. Sediment that is trapped in the bowl-shaped heads of nearshore canyons has been shown by marker stakes and other objects embedded in this fill, to creep slowly or slump intermittently downslope. This slow movement erodes the bottom and the sides of the lower part of the canyon by corrosion. The concentration of erosive forces at the base of the canyon walls commonly results in large overhangs and a cross-axial profile that has an hour-glass shape.
In areas where storm-induced bottom currents rapidly introduce sand-size non-cohesive sediments on slopes that exceed the angle of repose, spectacular quasi-liquid sand flows develop that erode both the existing sediment fill and the rock walls of the canyon. In Baja California, Mexico, sand flows have been observed that can be truly called "rivers of sand."
The motion pictures presented at this convention were collected over the past 5 years in La Jolla and Scripps Canyons off southern California, canyons that are cut in sedimentary rocks, and in San Lucas and Los Frailes Canyons on the eastern side of the southern tip of Baja California, Mexico, canyons that are cut in granite. The film depicts the sedimentary and erosional processes active in these canyons.
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