Richard Gates says:
Hi Mike, Read your interesting article on the Teahupoo wave. Looks to me like it is significantly affected by a phenomenon known as a "hydraulic jump". The flow off the reef exceeds the critical velocity for the formation of a wave in such a shallow layer (hence it is very smooth). Where the water becomes deeper, the wave is possible, almost as a standing or stationary wave, although in this case it does move forward against the draining current. The steep face is a characteristic of hydraulic jumps, which can occur as standing waves forming at the foot of drops in rivers, which are also used by surfers. The kinetic energy of the drainage flow is abruptly converted to potential energy to produce the sudden increase in depth as the drainage flow slows to a critical velocity where it reaches the deeper water at the edge of the reef. Another example of a hydraulic jump in rivers is tidal bores, which progress inland against the current as the tidal depth increases. These are also used by surfers. Hope this makes sense and I am not repeating comments by others. Cheers, Richard