Sediment Gravity Flows Warm-Up

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When grains are moved by gravity, rather than simply being carried by the motion of the fluid itself as in stream transport, we call the process a sediment gravity flow. These flows are either fluidal flows (viscous flows above the "liquid limit") and mass flows (flows exhibiting plastic behavior, below the liquid limit but above the plastic limit).

Fluidal flows include turbidity currents, fluidized flows and liqudfied flows. Mass flows include grain flows, which are right at the liquid limit, and mud and debris flows, below the liquid limit.

The different types of sediment gravity flows are also differentiated from one another by the process that keeps grains suspended in the flow.

Different types of mass flows produce different types of sedimentary structures, depending upon their degree of liquid or plastic behavior, and upon the mode by which the grains are suspended.

Essay question:

Use the concept of the degree of liquid or plastic behavior, and the process by which grains are suspended in the flow, to explain the difference between turbidity currents and debris flows. Then, describe the sedimentary structures, if any, resulting from these types of flows, being certain to relate the structures to the flow process, the degree of liquid versus plastic behavior, and the mode of particle suspension.

Multiple Choice Questions

Which of the following is (are) true regarding debris flows?

produce framework-supported deposits

result in poorly sorted deposits

deposits can be recognized by a strong fabric in elongated boulders

are matrix-supported

generally lack large particles

Which one of the following processes produces the most clearly defined vertical sequence of grain size changes and variations in sedimentary structures?

grain flow

fluidized flow

debris flow

mud flow

turbidity currents