Waterfalls are places where a river plunges vertically.
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 (see faults) or over a hanging valley (see glaciated landscapes).
Boulders often swirl around at the foot of a waterfall, wearing out a deep plunge pool.
Angel Falls are named after American pilot Jimmy Angel who flew over them in 1935.
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.
Niagara Falls has two falls: Horseshoe Falls, 54 m high, and American Falls, 55 m high.
The spectacular Iguacu Falls in Brazil are made up from 75 individual falls cascading 82 m into the gorge below.