Waves are generated by the friction of the wind on the surface of water. Wave erosion along the seashore results in the formation of cliffs of varying heights. As the waves break at the foot of the cliff, cliffs recede in land, gradually leaving a flat wave0-cut platform along the shore. Deposition of materials by waves results in the formation of beaches along the shore. Beaches may contain sand, pebbles or gravel in varying proportions. Wide beaches are developed on gently sloping shorelines. Deposition by waves may also result in the formation of narrow, elongated sandbars. The shallow sea between the sandbar and the shore forms a lagoon or marsh and gets gradually filled up by sediments. The shallow Kerala backwaters in the coastal areas are suitable examples of such lagoons.