A waterfall is a vertical fall of river water, caused by the existence of a clear rock threshold in the riverbed, from a few to several hundred meters high. The waterfall is found in the upper sections of the river flow, in places where the river crosses a layer of hard rocks. These rocks, washed out more slowly than the soft substrate at the bottom of the river, form the degree from which the water falls. A series of waterfalls is called a cascade.
