Geography - The Coastal Zone - Waves (7.1)

Waves are usually formed by the wind blowing off the sea. Friction with the surface causes ripples which develop to form waves. The stretch of open water over which the wind blows is called the fetch.

Longer fetch = more powerful wave.

Waves can also be formed by earthquakes or volcanic eruptions which shake the seabed.

These waves are called tsunamis. Example: December 2004 tsunami in the Indian Ocean which killed 240,000 people.

In open sea, despite the vertical motion of the sea, there is little horizontal transfer. Ot is only when waves approach the shore that there is a forward movement of water as waves break and wash up the beach.

The seabed interrupts the circular orbital movement of the water. As the water becomes shallower the circular motion becomes more eliptical. This causes the crest of the wave to rise up and then eventually topple onto the beach.

The water that rushes up the beach is called the swash. The water that flows back towards the sea is called the backwash.