Waterfalls

Formation of a WaterfallFormation of a waterfall

  • The river flows over bands of less resistant (softer) and resistant (harder) rocks.
  • The less resistant rock is more quickly worn away due to differential erosion.
  • The river erodes the rocks in three main ways:
    1. Hydraulic action – when the sheer force of the water gets into small cracks and breaks down the rock.
    2. Corrasion – when the river bed and banks are eroded by the load hitting against them.
    3. Corrosion – when the river water dissolves minerals from the rocks and washes them away.
  • The river undercuts the harder rock leaving an overhang which becomes unsupported and collapses into the plunge pool below.
  • After the overhang falls, some of the rocks are swirled around by the river and this helps to form a deep plunge pool below the waterfall. The plunge pool is also deepened during times of high discharge when hydraulic action is most powerful.
  • The waterfall is moved upstream, the process continues and a steep-sided gorge is cut back into the hillside.

Waterfalls, plunge pools and potholes