This is covered by:
AQA 8035, Cambridge IGCSE, CEA, Edexcel A, Edexcel B, Eduqas A, OCR A, OCR B, WJEC
The power of waves is one of the most significant forces of coastal change. Waves are created by frictional drag as the wind blows over the surface of the ocean. We often think of the air as being weightless and ‘nothing’ but in fact it has real power, as you discover when you try to walk into a gale! The same forces you experience when you walk into the wind are applied to the surface of the sea as the air is moved across it. Friction is created at the boundary between the air and water, pushing water in the direction of the wind. This creates a swell and a wave is created. Energy from the wind begins to rotate the water, turning it in a forward moving circle. In this way the wave can move forward and will continue doing so until it either reaches an obstacle, like land, or it runs out of energy, eg: the wind stops.
The two main factors that determine the size and power of a wave are the strength of the wind and the distance over which it blows. A strong wind blowing over hundreds of miles of ocean will create a more powerful wave than a weak wind blowing for just a few miles. The uninterrupted distance over which the wind can blow is called the fetch.
Waves are classified into two types: destructive and constructive.