Waterfalls:
● Waterfalls = water falls down a vertical drop in the channel over an area of hard rock followed by soft rock
○ Forms where there’s a junction between a hard rock capping upstream, and soft rock downstream
→ Characteristics:
● Hard rock layer on top of soft rock layer
● Overhang
● Bare rock
● White water
● Plunge pool
● Indentation
→ Formation:
1. Stage 1
○ Rocks are laid down horizontally
○ There is a junction between a hard rock capping upstream and soft rock downstream
○ Differential erosion takes place →
water falls vertically from hard rock to
soft rock below
2. Stage 2
○ Splashback causes hydraulic action
to weaken rocks behind fall of water
○ Pieces of soft rock break off
○ Indentation is formed at the base
○ Continued undercutting → hard rock
capping loses support and overhangs
3. Stage 3
○ Unsupported overhang breaks off
○ Fallen rocks break up and are caught
in flow of water
○ Some rocks get trapped and drill into
the bed → creates plunge pool
○ Undercutting continues, creating new
overhang
■ Repeated process of headward erosion → waterfall retreats upstream
Gorges:
● Gorge = a narrow, steep-sided valley with bare, rocky walls
→ Characteristics:
● Steep, high valley sides
● Located immediately downstream of a
waterfall
● River channel takes up most of the valley
floor
● Turbulent, fast flowing white water
● Many areas of bare rock on valley sides
● Boulders at the bottom of the river bed
● Process which takes thousands of years to
form
→ Formation:
1. Waterfall retreats upstream due to
undercutting/overhang drops
2. Leaves a steep-sided valley downstream →
gorge
3. Everytime overhanging cap rock breaks off
→ gorge retreats (moves back up channel)
and grows longer