There are three main processes at work in the sea. These are erosion, transportation and deposition.
Erosion is destructive waves wearing away the coast.
There are four main processes which cause coastal erosion. These are corrasion/abrasion, hydraulic action, attrition and corrosion/solution.
Corrasion/abrasion is when waves pick up beach material (e.g. pebbles) and hurl them at the base of a cliff.
When waves hit the base of a cliff air is compressed into cracks. When the wave retreats the air rushes out of the gap. Often this causes cliff material 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.
Corrosion/solution is when certain types of cliff erode as a result of weak acids in the sea.
You can view animations of each of these processes on"