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Pounding waves, crashing cliffs
When storm waves pound against the bottom of a cliff, even hard rocks can come crashing down.
Most of us visit the seaside when the weather is fine and the waves splash gently against the rocks. But it is not always like this. If we were to visit the seaside during a storm, we would find huge waves pounding against the cliffs and coastal structures (picture ). This is when rapid change can occur.
The wearing away of a cliff is called erosion. There are two ways that cliffs are worn away. One way is described here; the other way is shown on pages 14 and 15.
Water force
To understand how pounding waves can break up cliffs, just imagine a wave as a moving wall of water (picture ).
Water is very heavy. Moving water therefore carries a lot of force with it.
As a result, a wave crashing against the foot of a cliff can do considerable damage (picture 3).
Cliffs made of soft rocks stand little chance against fierce waves, and they simply crumble away. Some low cliffs can be worn
back by more than a metre during just one storm.
But even cliffs made from hard rocks can be weakened and eventually destroyed by waves.
Breaking waves
As a wave approaches a cliff, the front
of the wave rears up to form a curved, foaming top, or breaker. The breaker moves forward with great speed, throwing tonnes of foaming water against the bottom of the cliff (picture 2).
Water and air bubbles are forced into even the tiniest of cracks in the rock. As the main part of the wave crashes onto the cliff, the air and water in the cracks is squashed, and this is like driving a wedge into the cracks.
Once the wave has broken, it collapses, and the water and air in the cracks rush out again. Then, within a few seconds, a new breaker arrives and the process happens all over again.
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  Time-lapse pictures showing a wave breaking over a lighthouse during a storm.
This shows you the height of storm waves and gives a vivid idea of how powerful they can be.