Waterfalls, sometimes called cataracts, arise from an abrupt steepening of a river channel that causes the flow of water to drop vertically, or nearly so. Waterfalls of small height and lesser steepness are called cascades; the term is often applied to a series of small falls along a river. Still gentler reaches of rivers that nonetheless exhibit turbulent flow and white water in response to a local increase in channel gradient are rapids. Waterfalls are characterized by great erosive power. The rapidity of erosion depends on the height of a given waterfall, its volume of flow, the type and structure ...(100 of 32811 words)