The sheer power of the waves eg smashing against a cliff.
Trapped air is blasted into holes and cracks in the rock eventually causing the rock to break apart (cavitation).
The effect of rocks being flung at the cliff by powerful waves.
The rocks act as erosive tools by scraping and gouging the rock.
The dissolving of rocks such as limestone and chalk.
The knocking together of pebbles, making them gradually smaller and smoother.
The 'sandpapering' effect of pebbles grinding over a rocky platform, often causing it to become smooth.