Formation of waterfall

River erosion

Vertical erosion deepens the river channel as it flows over different rock types.

Differential erosion

Soft rock erodes faster than hard rock, creating a step in the riverbed.

Waterfall formation

The river flows over the resistant rock and drops vertically where soft rock has been eroded.

Plunge pool erosion

Hydraulic action and abrasion deepen a plunge pool at the base of the waterfall.

Undercutting

Erosion removes soft rock beneath the hard cap rock, creating an overhang.

Collapse of overhang

The unsupported hard rock collapses into the plunge pool.

Waterfall retreat

Repeated collapse causes the waterfall to retreat upstream (headward erosion).

Gorge formation