Waterfalls like rapids form mainly in the upper course as a result of differentiated erosion. If the river channel flows across
different bands of geology with varying resistance, then the softer less resistant rock will be eroded faster creating a step
in the river. The hydraulic action of the water enlarges this step over time creating the waterfall.
Due to the force of the water a deep plunge pool forms at the base of the waterfall. Turbulent flow with eddy currents
and splashback undercut the cap of resistant rock headwardly, until the undercut is significant enough for the rock above
to collapse under its own weight. This leaves angular resistant bedload in the plunge pool, which will combine with
hydraulic action to further deepen and undercut through the process of abrasion.