Material carried by the waves, when they bump into each other and so are soothed and broken down into smaller particles.
This process involves the force of water against the coast. The waves enter cracks (faults) in the coastline and compress the air within the crack. When the wave retreats, the air in the crack expands quickly causing a minor explosion. This process is repeated continulously.
This is the chemical action of sea water. The acids in the saltwater slowly dissolve rocks on the coast. Limestone and chalk are particularly prone to this process.
This is the process by which the coast is worn down by material carried by the waves. Waves throw these particles against the rock, sometimes at high velocity.