Water in Motion

Waves and water movement

Waves are undulations in the surface of a water body. Most waves are created when kinetic energy is transferred to water by the frictional stress of wind blowing over it. The resulting transfer causes a rise in water level producing a wave crest, followed by the sinking of the surface creating a wave trough. The wave length is the distance between successive crests. The time required for successive crests to pass a point is the wave period. The wave height is the distance between the crest of the wave and the still water level. Wave height is determined by (1) wind velocity, (2) duration of the wind, and (3) the fetch. The fetch is the distance of uninterrupted flow over an open water surface. An increase in any these factors will increase wave height and length. [See these effects using the "Savage Seas" Wave Machine. ]

Image of wave characteristics. Figure 21.5 Wave Characteristics (Courtesy Naval Meteorology Program and Oceanography Command "Restless Sea")

The rise and fall of oscillatory waves in an open water reflects the circular motion of water particles. There is relatively little forward motion by a water particle as a wave passes. It is simply the wave form and its energy that is transmitted across the ocean surface. Water particles move in circular orbits that diminish with depth. The radius of the circular path is greatest at the surface and decreases with toward the bottom of the wave. Larger waves exhibit larger orbital radii and extend to a greater depth than smaller waves. At some point in deep water, the wave has no effect on the motion of the water. Thus a zone of no wave motion exists from the base of the wave to the ocean floor. "Observe an animation of wave motion" (Courtesy NSF/TERC/McDougall Littell)

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For Citation: Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography.
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Michael Ritter (tpeauthor@mac.com)
Last revised 1/22/14