An animated presentation showing the processes at work which form waterfalls. Many of these slides have animations on them which can be viewed if you download this ppt.

1. The formation of a waterfall The formation of a waterfall

2. 1. Waterfalls are often formed where a layer of harder rock overlays a layer of softer rock. Harder rock Softer rock

3. 2. As the river passes over the softer rock, it is able to erode it at a faster rate, forming a step in the river bed. Harder rock Softer rock Harder rock Softer rock Harder rock Softer rock Harder rock Softer rock

4. Harder rock Softer rock i. deepens the step to form a plunge pool at the base of the waterfall ii. it undercuts the harder rock to form a notch Further erosion makes the plunge pool and notch bigger over time. 3. The force of hydraulic action does two things:

5. Harder rock Softer rock As the notch grows, eventually there isn’t enough support under the harder rock and so it collapses into the plunge pool .

6. Harder rock Softer rock This adds rocks and boulders to the plunge pool, and so the process of corrasion works with hydraulic action to further erode the plunge pool and notch .

7. The processes of erosion continue, further eroding out the notch and plunge pool. Eventually the harder rock above will collapse again, meaning that the waterfall will retreat upstream over time. Harder rock Softer rock

8. As it retreats, it leaves behind a steep sided gorge .

9. The formation of a waterfall The formation of a waterfall notch Side of gorge