Types of waves and erosion processes

Waves are formed by wind blowing over the sea. They are not to be confused with a 'tide' which is caused by the moon's gravitational pull. The friction with the sea floor sets the wave in motion.

There are two types of waves: constructive and destructive. As the name implies, destructive waves erode the shoreline more than they deposit sediment. On the other hand, constructive waves are more constructive to the shoreline as they deposit more than they erode.

Constructive

A constructive wave has a strong swash and weak backwash. It has a low wave energy hence it deposits more than it erodes. It has a small amplitude but a huge wave length. Beaches often become steeper as a result of the deposition.

Destructive

A highly energetic wave with a small swash but huge backwash, a destructive wave erodes the shoreline, making it smoother and slope at a gentle angle.

There are four predominant processes of erosion:

1. Hydraulic action
2. Attrition
3. Abrasion
4. Corrosion

1. Hydraulic action is the sheer force of waves against the cliffs. When waves break against the cliff surfaces, the water moves into cracks in the rock, compressing the air inside which increases the pressure. When the water retreats, the pressure immediately decreases and the air is expelled from the rock, causing a small explosion whilst doing so. When this occurs repetitively, the rock is weakened.

2. The process by which rocks and pebbles become more rounded and smooth as they crash and bump into each other.

3. The process by which the cliff surface is eroded by material carried by the waves.

4. Corrosion occurs when the sea is slightly acidic causing the rock to dissolve. This occurs more frequently in certain rock types.