external image Ocean-Waves-Free-Screensaver_2.jpgWaves on the sea are usually caused by the wind. Large ones can travel for hundreds of kilometres across the ocean. When they reach shallow water near land, they are slowed down at the bottom but keep going at the top, so they get taller and fall over. (They "break".)

Waves that are caused by the wind don't move the sea water from place to place (but the tide does). They move a bit like the ripples made by the wind in a field. The plants wave in the wind, but do not move along because they are rooted to the ground.

Waves can be dangerous but they can also be useful for sport, like surfing, and for generating electricity.

Occasionally, very large waves are caused by earthquakes under the sea. These are called tsunamis and can do a lot of damage.