The «phase velocity» describes how fast waves of a given wavelength move, and the «group velocity» describes how fast the light conveys energy or information. (sciencemag.org)
Fast waves breaking over shallow coral make for an adrenaline packed surf, and lots of nice coral cuts, so beware. (gili-paradise.com)
More exposed and typically surfed by advanced local surfers, the consistent sand banks at North Fistral provide steeper faster waves with peaks that break right and left. (cornishwave.com)