Nature · Earth Science
Where rivers leap over the edge
A waterfall is a place where a river or stream flows over a vertical drop or steep series of steps. Beyond their beauty, waterfalls mark points where erosion is especially fierce — and they slowly retreat upstream as the falling water undercuts the rock beneath.
Most waterfalls form where a band of hard rock lies over softer rock. The river erodes the soft rock faster, leaving a lip of resistant rock over which the water plunges. The force of the fall carves a deep plunge pool and undercuts the lip, so the waterfall gradually migrates upstream.
Hard caprock resists erosion while softer rock below is scoured out, undercutting the lip and carving a deep plunge pool.
Water falls free from the rock
The purest kind of fall: the river shoots clear of the cliff and plummets straight down, hammering out a deep plunge pool where it lands.
Immense, thundering walls of water
Cataracts are the giants — vast, powerful curtains of water carrying enormous flow, throwing up clouds of mist visible for kilometres.
Water tumbling down rocky steps
Instead of one drop, cascades tumble down a natural staircase of rock, splitting into white, foaming ribbons that step down the slope.
Water clinging to the rock face
Here the water stays pressed against the cliff as it slides down, spreading into a shape like a horse's tail rather than falling free.