Monica Sappleton
Monica Sappleton answered
A waterfall is formed when the shelly soft rocks in a riverbed are eroded. This causes the overlaying "hard rocks to collapse, and the water in the riverbed can no longer flow at it's former speed, but plunges over the collapsing rocks as shown in this waterfall: Http://authspot.com/poetry/a-tale-of-a-melody-without-rhythm-from-the-dunn%e2%80%99s-river-falls/