Alternate up and down movement of ocean water is called waves. The frictional drag in the waves is caused by the wind. The stronger the wind, the stronger are the waves. Similar to other agents of gradation, waves also do erosion, transportation and deposition. When the waves strike the coast they cause erosion and wear away the rocks. The softer rocks get eroded much faster than the harder rocks and different features such as the cliffs, wave cut platform, bays gulfs, and etc. is formed. When the waves recede they transport the eroded particles such as sand, silt, pebbles, stones, etc. and deposit them in these areas. The erosional and depositional features formed by the waves are:
(a) Gulf/Bays where there are horizontal bands of hard and soft rocks lying perpendicular to the coast. The waves erode away the softer rocks faster forming inlets known as gulfs and bays.
(b) Cliffs and wave cut platforms when there is a highland overlooking the sea, the base of the highland/cliff gets eroded forming a notch. The notch gets deepened by the waves and when they retreat, deposits the eroded materials forming a platform. The wave cut platform is formed when the sea cliff shifts backward due to continuous wave erosion.
(c) Beach is a depositional feature formed by the waves. Advancing waves like other agents of gradation also cause erosion, transportation and deposition. The advancing waves strike the coast and erode the rocks. The materials consisting of pebbles, stones, sand and other materials are deposited along the shore in the shallow water. The deposition leads to the formation of beaches which stretch along the coast, e.g., Kovalam beach, Juhu beach, Triplicane beach, etc.
Sand bars and lagoons when the waves recede the eroded materials may be deposited perpendicular to the coast forming a tongue like feature known as sand split.
Due to the change in the direction of the wind, waves change their direction. The deposits may be deposited at right angle to the sand spit and parallel to the coast forming a sand bar. The sand bar sometimes gets closer to the shore enclosing a part of the saline water of the ocean. These are known as lagoons. Lagoons are backwater or brackish water lakes. They have a narrow link with the ocean water. Lagoons are commonly found off the coast of Kerala on the west coast of India and on the east coast of India, e.g., Chilka Lake, Pulicat lakes.