The waves carry the sand to the sea and leave the sand on the bottom floor of the ocean. During calm periods, erosion reverses. The sand is moved offshore and slowly land ward by the orbital motion of gentle waves. The ocean currents and waves keep the beach in perpetual motion. The existence of cliffs on a coast indicates that erosion is taking its toll on the beach.
Waves hurl themselves at the cracks in the cliff wall.
The pressure of the water and the compressed air creates a wider crack, causing the earth to break off into pieces. More waves grind the pieces of earth together to make sand. The chemical reaction of salt water and oxygen breaks down rocks which come into contact with sea water. When every wave breaks on the beach, a thin layer of sand is carried along. When the wave retreats, the sand is taken back to the surf zone.