There are four main processes which cause coastal erosion. When waves hit the base of a cliff air is compressed into cracks. Often this causes cliff matrial to break away. This process is known as hydraulic action .
Attrition is when waves cause rocks and pebbles to bump into each other and break up.
Cliff Recession Erosion is greatest when waves break at the foot of a cliff. This causes erosion at the base of the cliff. This creates a wave-cut notch in the base of the cliff. As the notch increases in size the weight of the cliffs above become too much and the cliff collapses. This material will provide temporary protection for the cliff behind.