Waterfalls

Waterfalls may form where the river flows over a band of hard rock, such as a volcanic sill. The river erodes the soft rock below but it has little effect on the hard band. Waterfalls can also form where a stream's course has been suddenly broken, for example where it flows over a cliff into the sea, over a fault or over a hanging valley.

Boulders often swirl around at the foot of a waterfall, wearing out deep plunge pool.

Victoria Falls in Zimbabwe are known locally as Mosi oa Tunya, which means "the smoke that thunders". The roar from Victoria Falls can be heard 40 km away.

Niagara Falls on the US/Canadian border developed where the Niagara River flows out of Lake Erie. Nigara Falls has two falls: Horseshoe Falls - 54 m high, and American Falls - 55 m high.