The formation of waterfall

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 waterfallThe formation of a waterfall

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

3. Harder rock
Softer rock
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

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 waterfallThe formation of a waterfall
notch
Side of gorge