River landforms

Waterfalls.

Waterfalls form where a band of hard rock meets softer rock, which is eroded more than the harder rock causing a step in the river bed. The water flowing over the step speeds up due to the lack of friction as it drops over the step, and the increase in speed gives the water greater erosive power. This causes further erosion of the soft rock and undercutting of the harder rock. As the hard rock is undercut, it can collapse, causing a plunge pool which is carved out by abrasion as the its of collapsed rock are swirled round by turbulence. Over time, more undercutting causes more collapse so the waterfall retreats up the channel leaving behind a steep-sided gorge.

Potholes.

These are small circular hollows in the river bed formed by abrasion as turbulence swirls the river's bedload round in a circular motion causing it to rub and scrape out holes.

Rapids.

These are relatively steep sections of the river with turbulent flow where there are several sections of hard rock, a bit like mini-waterfalls.

Meanders.

Meanders form where alternating pools (areas of deep water) and riffles (shallow water) develop at equally spaced intervals. As the river channel is deeper in pools it is more efficient so has greater energy and more erosive power and energy is lost as the river flows over a riffle because of friction. The spacing and distance between riffles and pools causes the river's flow to become uneven and maximum…