Destructive waves erode the coastline in a number of ways: Hydraulic action. Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.
Abrasion. Bits of rock and sand in waves grind down cliff surfaces like sandpaper.
Attrition. Waves smash rocks and pebbles on the shore into each other, and they break and become smoother.
Solution. Acids contained in sea water will dissolve some types of rock such as chalk or limestone.