Geography Revision

Formation:

1. A band of hard rock lies over a band of soft rock.

2. Soft rock is eroded by hydraulic action, which creates a step in the river bed.

3. Further erosion by hydraulic action, erodes the soft rock and undercuts the hard rock.

4. When the hard rock is undercut, it collapses as there is no rock beneath to support it. 

5. The hard rock material collapses and erodes the river bed into a plunge pool, carved out by abrasion. 

6. A plunge pool is carved out at the foot of the waterfall, as pieces of collapsed rock are swirled by turbulent flow. 

7. Over time, more undercutting causes more collapse.

8. The waterfall will retreat (move back up the channel), leaving behind a steep sided gorge.