Explain the processes involved in the formation of a waterfall. (6 marks)

A waterfall is an erosional landform, which occurs where there is a layer of hard rock on top of a layer of softer rock. Erosional processes such as hydraulic action and abrasion occur as the river flows downstream, however differential erosion takes place as the softer rock erodes faster. Over time, the softer rock is gouged out and leaves the harder rock overhanging. The hard band of rock can no longer support itself and breaks off adding more material for erosion into the river and the plunge pool at the base of the waterfall. Material collected in the plunge pool deepens the waterfall, again through hydraulic action and abrasion. Overtime, the waterfall retreats upstream and leaves a steep sided gorge behind.