WAVES

Waves begin when storms at sea transfer wind energy to the water via the friction between the two.  Initially, where the waves are first formed underneath the storm, they move chaotically, but as the wave energy spreads into a larger part of the ocean they organize into concentric circles of wavefront moving in a very organized fashion away from the point of origin.  A simple model occurs when a stone is thrown into water.  The energy of the initial chaotic splash is transformed into a ring of wavefronts just as the storm energy is in real ocean waves.

The diagram summarizes the parts of a wave train and generally how the wave behaves in deep water.  Note that the wave is symmetric, sloping consistently in both directions from each crest into each trough.  The distance from trough to trough or from crest to crest is called the WAVE LENGTH.  The vertical difference between the elevations of the crests and the troughs is called WAVE HEIGHT.  As the bottom part shows there is no net movement of water as a wave passes.  The water is simply a medium for moving the energy of the wave.  Each particle of water and any floating object simply makes a circular trip as the wave passes, ending up just where it began.  The diameters of these circular paths decrease regularly downward so that at some depth the water does not move at all.  This depth is called WAVE BASE.  Sediment on the bottom of a sea that is deeper than wave base will not be eroded or moved by the waves.  The depth to wave base is ALWAYS equal to 1/2 the wave length.

 

There is, as you might expect, a relationship between the amount of energy a wave moves and the size of the wave.  More energy makes bigger waves, and both the wave height and length are affected.  For any wave train the waves are consistently high within any particular part of the train, though declining overall toward the "back" of the train.  Wave height and length are mathematically related such that height equals 1/7th length.

The speed of wave advance ("celerity") also depends on energy and wave size.

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