Mighty waves strike like hammers against the cliffs on the seashore, loosening chunks of rock that fall into the water. The churning waves smash broken rocks against the cliff and one another, breaking up the bigger boulders into stones. The action of the waves smoothes the stones into rounded pebbles and grinds the pebbles into grains of sand. Rain and frost also weaken cliffs and send them tumbling into the sea, which starts breaking them up and grinding them down.
