This kind
of erosion is called 'coastal erosion', usually caused by waves or high winds. Abrasives
in the water or impact against the rock can cause it to chip off or degrade
over time.
One of the
causes of coastal erosion, which might best fit your question, is hydraulic
action. This describes the impact of the wave hitting the surface of the rock
or cliff. The wave compresses air inside cracks on the rock, and the pressure
causes the rock to splinter off.
