Wind waves approaching the shore break. As the wave train reaches water less than half its wavelength, the wave hits bottom. The circular move of the water molecules is interrupted. The waves energy must now be packed into less water and the wave crests change from round (circular) to peaks. As the friction of the bottom slows the wave, wavelength decreases but period remains unchanged. The wave becomes too high for its wavelength, approaching the critical 1:7 ratio. The water on the bottom is slowed down but the water in the crest moves ahead and breaks.

Below: Wave action has eaten (gnawed) on this coast line. Wind and rain have helped with the erosion of the soft layers the cliff is made off at Stillwell hall at the former Ford Ord property.

(Link to ocean resources, Baum)