The surf zone is one of the most dynamic regions of the marine environment. Not only is it highly energetic, it also supports a wide diversity of life forms. Surf zones in both sandy and rocky shores produce dynamic surroundings that shape the entire coastal region.
Waves are initiated at sea where winds sweep across the surface of the water . Some of the energy of the wind is transferred to the surface and small sinusoidal waves appear on top of the water. The wave often increases in energy with added winds. The height of oceanic waves is dependant on the energy of the wind which may be quite high during storm events.
The waves continue until they reach the shore. Once there, they strike the shore and lose their energy. What happens during this process is of great importance to geologists and those who live near the beach.
Ocean waves are very interesting examples of wave physics found in nature. A look at the wave in cross-section appears as a series of linked "S" shapes. The high point of the individual curve is called the crest. The low point is the trough. The size of the individual waves (the amplitude) and the frequency (the rate at which a series of waves pass a particular point during a specific amount of time) are determined by the amount of energy a group of waves contains.
The long waves strike the shore at an angle. Waves will rarely, if at all, touch the shore at a parallel line to the shore. This is a result of the changing topography of the land. When the wave strikes the shore it is refracted and a great deal of its energy is directed at an oblique angle to the original wave. This increases the energy of the wave effect and, for anyone who has experienced it, produces a significant push-pull type of action. Being caught in this area , named the swash, can be dangerous under certain conditions such as rip tides formation.
Geologists are concerned about the region where waves break on the shore. Small circular currents occur in the water that produce the characteristic swell shape. As these circular currents reach the shore and strike the bottom, they are compressed. This compression eventually breaks down the wave structure and the water spills over on itself at the crest. This is the point at which waves are commonly called "breakers." The bottom sediments act as a further drag on the wave and deplete it of much of its energy. Any sediments that were initially captured by the breaking wave are dumped and moved onto the beach. At the same time, the refracted wave captures sediment and pulls it back down the shoreline. This repeated motion causes sand grains to migrate down the beach as waves strike again and again. Where the shore is rocky, the force of the waves wears away the rocks and transports smaller clasts (sedimentary particles) out to sea and the coast. This type of erosion is a major physical process that sculpts cliffs around the world. The entire area of breaking waves, including the slope-face of the land, is called the surf zone.
See also Beach and shoreline dynamics; Dunes; Sedimentation; Wave motions