Abstract

Slumps and sediment-gravity flows have been identified in Holocene glaciomarine sediment on declivities less than 1.3 degrees on the Gulf of Alaska continental shelf. Geologic and geotechnical investigation suggest that the processes responsible for these slope failures are earthquake and storm-wave loading, coupled with cyclic degradation of the sediment-shear strength. We propose that the failure type is related to the nature of the failure load. For example, a slump that occurs approximately 30 km seaward of Icy Bay in water depth of 70 to 150 m was most likely caused by earthquake loading, whereas sediment-gravity flows on the Alsek prodelta, which occur in water depths of 35 to 80 m, probably were caused primarily by storm-wave loading. Sediment remolding and redistribution and incorporation of water, which occurs more readily during wave loading from a long storm than during the limited number of loading cycles generated by an earthquake, reduces the shear strength and increases the fluidity of the failed sediment mass. Wave-induced slope failures thereby tend to transform into sediment-gravity flows.

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