Another type of plunge pool is formed under a vertical displacement of water, for example a waterfall or rapids. Because of the hydraulic action acted there, the plunge pool interiors are irregular and rough. Plunge pools are created by the pressure of the water either from a waterfall or rapids. The water swirls around fallen rocks and gradually makes a deep pool.
A plunge pool is formed when a waterfall plunges from great height and hit the river bed with tremendous force. With repeated pounding of the waterfall, a depression known as a plunge pool is formed. It is further deepen as boulders and rocks swirl around it.