Describe and explain how one fluvial landform is formed with reference to an example.

A waterfall is an erosional fluvial landform, characterisedby a steep drop in the river. It is formed in the upper course when verticalerosion forms a V-shaped valley. For instance, High Force is the UK’s largestwaterfall – 21 metres high – located on the River Tees in NE England. An areaof hard impermeable igneous rock called Whinstone is located above a layer ofsofter rocks, such as limestone and sandstone. The softer rock is eroded by acombination of hydraulic action and abrasion, undercutting the harder rock.This leaves an overhang of unsupported rock, under which a plunge pool is formed.Over a period of thousands of years, the waterfall gradually retreats up streamas the force of gravity pulls down the overhang causing it to collapse and forminga steep-sided gorge.