Waves

Here's a very brief look at the way in which waves and surf are produced.
A wave coming out of deep water into the shallow water of a beach or reef will be traveling at about 15 to 20 mph and will start to 'drag' on the sea floor. This shortens its wave length, which in turn increases the steepness of the wave, tending to make it less stable. This is the prelude to the wave breaking, which will eventually occur in water that has the depth of about 1.3 times the wave height, so you could expect to find a 6ft wave breaking in water just over 4.5ft deep - in theory. This may may not always be the case.
The energy released by a breaking wave is phenomenal - large waves have been recorded exerting a force of 6,000 pounds per square foot in the surf, or impact zone; so its hardly surprising that a bad wipeout can be such an memorable experience! Once a wave breaks, it will generally take one of three forms; surging, spilling, or plunging.

• Surging Waves
  These are of little use to surfers. They come in out of relatively deep water on to steep beaches, rather than break, surge up the beach. You may witness this on some surf beaches at high tide when the profile of the beach becomes too steep to enable the wave to break properly.
  
• Spilling Waves
  The most common type to be found on British beaches. They are produced by a gently sloping sea bed, which causes the wave to peak gradually: the release of energy from the wave is relatively slow, so the crest 'spills' down the wave face.
  
• Plunging Waves
  These are the spectacular waves of which the surfing magazines are full. Good examples are Pipeline in Hawaii and Thurso East in Scotland. Plunging waves are more likely to occur at reef breaks than on beaches.