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Debris flow, a gravity-transport mechanism commonly observed on land, may be a significant agent of high-density mass transport of sediment in the oceans. Debris flow is distinguished from other mass-transport agents by the mechanism of support of granular solids in the flow. Support is provided mainly by the strength of the debris, but also by buoyant forces. Strength is derived from the fluid phase of the debris (clay minerals plus water), which acts as a plastico-viscous material. Suspension of granular solids by this mechanism does not depend on flow conditions and occurs if the debris is moving very slowly or even not at all. Movement of a debris flow depends on a critical thickness of the debris as well as the internal-friction angle. The slope angle required for de ris flow typically is less than the 18-37° required for normal grain flows or avalanching. Thus, debris flow may carry large amounts of sediment in suspension while moving sluggishly down a gentle slope. The amount of clay, relative to granular solids, necessary completely to support sand-size material is on the order of 10% or less. Thus, sandy debris-flow deposits may be texturally similar to current-deposited sands.
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