Explain the formation of a waterfall.

Waterfall formation occurs in areas with bands of soft and hard rock (the cap rock). In these areas soft rock is eroded much quicker and easier by the water, creating differential erosion. This causes the lowering of the bed underlain by soft rock and in turn creates a dip in the soft rock. This dip causes an increase in the energy carried by the water which increases the erosive power of the stream, gradually the dip becomes larger and larger creating a vertical drop (the water fall). At the base of the waterfall a circular plugepool is created due to the erosive power of the falling water and the erosion of the soft rock back wall, this is known as headward erosion. Eventually, the cap rock becomes so undercut by headward erosion that it can no longer support itself, collapses, and causes the waterfall to retreat upstream. It is this process of retreating that creates the steepsided cliffs often seen near waterfalls known as gorges.