In fluid dynamics, a gravity current is a primarily horizontal flow in a gravitational field that is driven by a density difference, hence gravity currents also sometimes being referred to as "density currents". When a gravity current propagates along a plane of neutral buoyancy within a stratified ambient fluid, it is known as a Gravity Current Intrusion. Typically, the density difference is small enough for the Boussinesq approximation to be valid. Gravity currents can be either finite in volume, such as the release from a dam break, or continuously supplied from a source, such as in doorway or lava flows.