Everything from earthquakes to ship wakes creates waves; however, the most common cause is wind. As wind passes over the water's surface, friction forces it to ripple. The strength of the wind, the distance the wind blows (fetch) and the length of the gust (duration) determine how big the ripples will become. Waves are divided into several parts. The crest is the highest point on a wave, while the trough, or valley between two waves, is the lowest point.Wavelength is the horizontal distance, either between the crests or troughs of two consecutive waves. Wave height is a vertical distance between a wave's crest and the next trough. Wave period measures the size of the wave in time. A wave period can be measured by picking a stationary point and counting the seconds it takes for two consecutive crests or troughs to pass it.

In deep water, a wave is a forward motion of energy, not water. In fact, the water does not even move forward with a wave. If we followed a single drop of water during a passing wave, we would see it move in a vertical circle, returning to a point near its original position at the wave's end. These vertical circles are more obvious at the surface. As depth increases, their effects slowly decrease until completely disappearing about half a wavelength below the surface.


*Watch the water droplet move in a vertical circle as the wave passes. The droplet moves forward with the wave's crest and backward with the trough.*

Information provided by: http://www.onr.navy.mil