As it has already been explained, when a wave breaks, both water and wave energy move forward against the shore. The force of the water itself as it is thrown forward in the breaking waves bring about a remarkable wear and tear of the rock exposed to them.
The striking force of waves breaking on the shore exerts sufficient hydraulic pressure that can shatter rock masses into fragments. Besides, air in joints and cracks is suddenly compressed by the impact of the wave and with its recession, the compressed air expands with explosive force pushing out large blocks of rocks.
The effect of hydraulic action becomes more conspicuous during intensive storms, when the waves hit the shore which can be as great as 38 tonnes per square metre which is sufficient enough to bring about erosion along the coast. Besides, the force of water alone is enough to be effective in dislodging fractured blocks.
The following factors affect the hydraulic action to a great extent.
(i) Strength of the rocks along the shore.
(ii) Structural features of the rock.
(iii) Configuration of the coast-line.
(iv) Force of the water