Sediment gravity flows

A sediment gravity flow is one of several types of sediment transport mechanisms, of which most geologists recognize four principal processes. These flows are differentiated by their dominant sediment support mechanisms, which can be difficult to distinguish as flows can be in transition from one type to the next as they evolve downslope.

Sediment gravity flows are represented by four different mechanisms of keeping grains within the flow in suspension.

Although the deposits of all four types of sediment support mechanisms are found in nature, pure grain flows are largely restricted to aeolian settings, whereas subaqueous environments are characterized by a spectrum of flow types with debris flows and mud flows on one end of the spectrum, and high-density and low-density turbidity currents on the other end. It is also useful in subaqueous environments to recognize transitional flows that are in between turbidity currents and mud flows. The deposits of these transitional flows are referred to by a variety of names, some of the more popular being "hybrid-event beds (HEB)", linked debrites" and "surry beds".Powder snow avalanches and glowing avalanches (gas-charged flows of super heated volcanic ash) are examples of turbidity currents in non-marine settings.

Modern and ancient (outcrop) examples of deposits resulting from different types of sediment gravity flows.

Grain flows (sand avalanches) on the slip faces of sand dunes at Kelso in the Mojave desert, California

Dish structures in the deposit (Bouma A, Lowe S3) of an ancient liquefied sediment flow preserved in outcrop.

Debris flows filling a gully after intense storms of 2010 in Ladakh in the Himalayas.

Debris flow deposit in outcrop showing free-floating large clasts suspended in a clay matrix.

A powder snow avalanche is a form of turbidity current where air is the supporting fluid.

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