Quicksand

Synonyms

Drift sand; Mire; Quagmire

Definition

Quicksand is sediment of low bearing capacity caused by high volumes of water, or more rarely air, and a resultant decrease in the intergranular pressure due to disturbance. Quicksand is not any special type of sand, but instead it is a condition of zero effective stress.

The condition may occur in sediment with either standing water or flowing water. In the former case, the condition can be triggered by ground shaking (liquefaction). Most quicksand occurs in settings where there are natural springs, either at the base of alluvial fans, along riverbanks, or on beaches at low tide. In such cases, the loose packing is maintained by the upward movement of water (Fig. 1; Long 2002).

Fig. 1

Schematic diagram of how quicksand is often formed. Upward flowing water decreases the effective stress holding the sediment together. The sand particles rearrange or collapse