waterfall

A waterfall is a point in a river where water drops vertically or nearly so as it flows over a ledge or falls due to a drop in bedrock elevation. They commonly form where a river crosses a boundary between differently resistant rocks or where tectonic uplift creates a drop. Over time, the ledge undercuts, an overhang develops, and the unsupported rock collapses; the waterfall then retreats upstream through headward erosion, often cutting a gorge.

Waterfalls vary in shape and behavior. Common types include plunge, where water drops vertically and loses contact with the bed; horsetail, in which the flow adheres to the rock as it descends; cascade, over a series of steps; punchbowl, with a broad lip and circular plunge pool; and curtain, a thin sheet of flow. Some waterfalls are multi-step or tiered, with several drops in a sequence.

Hydrology influences a waterfall's character. Flow can be seasonal, swelling after rains or snowmelt. A base plunge pool, spray, and mist create microhabitats; waterfalls often feed rivers with dissolved minerals and can drive erosion at the bed and banks.

Ecology and geology: Waterfalls shape landscapes through erosion and deposition and support specialized plant and animal communities in the spray zone. They can alter sediment transport and influence river morphology downstream.

Human use and safety: Waterfalls attract tourism and can be exploited for hydroelectric power. They pose hazards such as rockfalls, flash floods, and slippery access; many are preserved in protected areas.

Notable examples include Niagara Falls on the U.S.–Canada border; Victoria Falls on the Zambezi River; Iguazú Falls on the Iguazú River; Angel Falls in Venezuela; and Yosemite Falls in California.