Wikipedia:POTD column/April 2, 2006

A waterfall is usually a geological formation resulting from water, often in the form of a stream flowing over an erosion-resistant rock formation that forms a sudden break in elevation. Waterfalls may also be artificial, and they are sometimes used for garden and landscape ornament. Some waterfalls form in mountain environments where erosion is rapid and stream courses may be subject to sudden and catastrophic change.

Photo credit: Diliff
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