Many waterfalls occur where rivers flow over hard rocks which overlie softer ones. The hard rocks resist erosion, while the softer rocks are worn away. The hard lip of the waterfall often overhangs the softer rocks and slabs of hard rock sometimes break off and crash downwards. In this way, waterfalls, like southern Africa’s Victoria Falls (whose African name means ‘the smoke that thunders’), gradually move upstream. Other waterfalls occur along cliffs, like those bordering steep-sided valleys, or ice-worn troughs.
The highest waterfall, Angel Falls in Venezuela, was named after an American pilot, Jimmy Angel, who was the first non-Amerindian to see it. Its total height is 979 m (3,212 ft), with one unbroken drop of 807 m (2,648 ft).