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. Big waves have more power to hold more sand particles in suspension and take sand off the beach than smaller waves. Both the energy and the steepness of a large wave carry the sand seaward.