Explain how waterfalls are formed.

Waterfalls are mainly found in the upper course of a river. They are formed where there are alternating bands of hard and soft rock along the river bed. This is because soft rock erodes around ten times quicker than hard rock. So, the falling water and rock particles erode the soft rock, creating a step in the river. The soft rock begins to be undercut by erosional processes such as, hydraulic action and abrasion which creates a plunge pool and at the same time an overhang of hard rock starts to develop. As these processes continue the step turns into a drop, the plunge pool becomes deeper and the overhang becomes larger and is unsupported. Eventually the overhand will collapse and the hard rock falls into the plunge pool providing it with more material and thus more erosive power. These processes continue forming a waterfall. The waterfall retreats upstream which leaves behind a steep-sided gorge. A prime example of this is Angel Falls in Venezuela.