Exposed rocks along the coastline can be broken down by the processes of weathering.
Freeze-thaw weathering occurs when rocks are porous (contain holes) or permeable (allow water to pass through).
Plants and animals can also have an effect on rocks. Roots burrow down, weakening the structure of the rock until it breaks away.
Rainwater and seawater can be a weak acid. If a coastline is made up of rocks such as limestone or chalk, over time they can become dissolved by the acid in the water.