Waves and Wave Action

What are Waves?
Waves are generated far out to sea when the surface of the sea is disturbed by the wind or the gravitational effects of the moon or sun. (Occasionally other forces such as earthquakes, landslides or explosions can cause waves).

The size of a wave depends on its fetch ( the distance that the wave travels) and the wind acting on the wave. The greater the fetch, the larger the wave and the stronger the wind the larger the wave.

All waves share certain inherent characteristics. The animation below defines some of those characteristics and how the water within a wave moves.

Use the link below to choose the length, period and height of a wave to see how it would affect you if you were out in a sailing boat.
(The terminology used here is explained in the animation above)

Breaking Waves
As a wave approaches a beach it slows. This is the result of friction between the water and the beach. This causes the wave to break.

There are two main types of wave; constructive and destructive waves.

Constructive waves
Constructive waves help to build beaches by accretion (material is deposited on the beach, adding to that already there). Each wave is low. As the wave breaks it carries material up the beach in its swash. The beach material will then be deposited as the backwash soaks into the sand or slowly drains away. These waves are most common in summer.

Destructive waves
Destructive waves destroy beaches. The waves are usually very high and very frequent. The back wash has less time to soak into the sand. As waves continue to hit the beach there is more running water to transport the material out to sea. these waves are most common in winter.

In addition to removing sediment from the beach in the backwash, (otherwise knows as hydraulic action) destructive waves can also affect the coast in several other ways.

1. The action of each powerful wave can cause move rocks and pebbles already on the shore causing them to smash into each other and break up and become smoother this is known as attrition.

2. Abrasion- Pieces of rock and sediment carried within the wave hit the cliff line or material at the back of the beach and begins to wear it down.

3.Finally acids contained within the seawater can act directly on certain types of rock, such as chalk or limestone, to dissolve it in solution, slowly wearing the cliff away, eventually causing failure of the cliff .