saltation

Saltation is a mode of sediment transport in fluids in which granular particles are intermittently lifted from the bed and travel along ballistic, curved trajectories before impacting the surface again. It occurs in air (aeolian saltation) and in water (subaqueous saltation) and is especially important for moving sand-sized grains. It lies between rolling or sliding along the bed and suspension of particles in the flow.

Initiation requires the fluid to exert enough shear or lift to overcome gravity and cohesion. Once lifted, a particle follows a short arc under gravity; its impact can eject other grains, sustaining a chain reaction that forms a saltation layer above the bed. The hop length and height depend on particle size, density, fluid velocity, and viscosity. In air, hops are typically centimeters to decimeters high, and lengths range from tens of centimeters to meters; in water, hops are shorter and lower.

In deserts and beaches, aeolian saltation drives dune and ripple formation and sand flux; in rivers and coastal environments, saltation forms part of bedload transport and contributes to scour and sediment mixing. The term derives from Latin saltare, meaning “to jump.”