Waterfalls (Fluvial Erosion)

Question 1

What can waterfalls be a result of?

Answer 1

• resistant band of rock occurring across the course of the river
• the edge of a plateau
• the rejuvenation of the area, giving the river renewed erosional power as the sea level falls

Question 2

How are waterfalls formed?

Answer 2

The river falls over a rock edge into a deep plunge pool at the foot of the fall, where the layers of weak rock are excavated more quickly than they overlying resistant rock.
The force of the swirling water around the rocks and boulders enlarges and deepens the plunge pool by hydraulic action and abrasion.
This undercuts the resistant (cap) rock above. Eventually this collapses and the waterfall retreats upstream leaving a gorge ahead of it.

Question 3

When do waterfalls and rapids occur?

Answer 3

When there is a sudden change in the gradient of the river as it flows downstream.