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Benson, Becky

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Bermuda

Bertlemann, Larry

Differences from wave to wave are nearly infinite, but the basic principles of wave formation and travel are constant: storm winds blow across the ocean surface and create a transfer of energy into the water; the energy is parceled, stored, organized, and rhythmically broadcast into surrounding oceans and seas until reaching shallow water (usually a coastline, often thousands of miles distant from the storm source) and releasing the energy as breaking waves. Waves are captivating not just to surfers, sailors, and oceanographers, but to nearly anyone who has looked upon an incoming swell; waves have served as the muse to artists, writers, filmmakers, photographers, and poets. Lord Byron, the 19th-century British poet and rogue, bodysurfed off the Brighton coast, and later wrote about the experience in 

 "Once more upon the water! Yet once more! And the waves bound beneath me as a steed that knows his rider." Waves, it is often said, are what raise surfing above all other forms of sport. "When we surf," Australian surf journalist Nick Carroll wrote in 1989, "we are riding on pure energy, part of the roaring pulse that runs across the universe."

The wave-making process begins with solar heat, which creates uneven atmospheric pressure areas over the earth's surface, which in turn produces wind-driven storms. The initial wind from a young ocean-borne storm creates ripples, or capillary waves, on the water surface. As the wind gains purchase on the backs of the small and nearly inchoate capillary waves, they begin to merge, forming and reforming into ever-bigger waves, in a growth cycle that continues until the wind stops or gravity restricts further growth. Three factors determine initial wave size: wind strength, duration, and fetch (the distance over which the wind blows). Discrete but linked waves now peel away from the storm front in a long, unbroken, corrugated "wave train," which, if strong enough, can move for thousands of miles with no further assist from the wind. (The aggregate waves from a given storm are called a "swell"; long-distance swells are often referred to as "ground swell.") Individual waves within a swell might be imagined, in cutaway, as rolling wheels of energy, most of which is efficiently submerged below the ocean surface.

As the swell radiates out through the water—a large, organized swell will travel about 25 miles per hour—the waves begin to organize themselves into sets, with the fastest waves moving out in front and the slower waves grouping up behind them. Similar to a pack of bicyclists, slower waves conserve energy by drafting off the lead waves, which in turn slow down and relinquish the lead position to the next fastest wave. By this process, waves expend a minimal amount of energy as they travel. Swell size and character can be altered by crosshatching against another swell (or multiple swells) or by meeting up with another wind front. But if the swell is given a clear oceangoing run, two things will happen: 1) Individual waves within the swell will move further apart from one another, increasing the "period," or the amount of time it takes succeeding wave crests to pass a stationary point; better wave quality is often directly linked to longer swell period. 2) The swell gradually but steadily will drop in size, losing one-third of its height for every doubling of the swell period.

Waves slow down as they approach land and begin making contact with the ocean floor. Some energy is lost to land-contact friction, but most is pushed up to create a larger, steepening wave. The wave breaks as the ground-dragging bottom portion of the wave is essentially overtaken by the cresting top portion, which spills over. Under neutral conditions—no wind, smooth swell, a gradually sloped bottom—a wave will break when the water depth is roughly one-third greater than the wave's height. If the ocean floor changes abruptly from deep to shallow (common to mid-ocean island reefbreaks), the bottom of the wave will slow abruptly, causing the crest to pitch forward and make a tubing wave. Conversely, if the ocean floor is gradually angled (common to all nearshore zones featuring a continental shelf), the top of the waves will be slow in overtaking the bottom, resulting in rolling, easy-breaking waves. Depending on the bottom topography and the shape of the coastline itself, incoming swells often refract (bend), resulting in a swell line that, viewed from above, becomes either concave to convex to the shoreline. As virtually all coastlines are uneven and scalloped to one degree or another, refraction of some kind is nearly as common to wave formation as wind itself.

The angle between a surf break and the incoming swell is crucial to wave shape and size at that particular break. Lower Trestles, a pointbreak in Southern California, responds best to swells angling in from the south or southwest, and is all but unridable during a northwest swell. Upper Trestles, just a few hundred yards away, is mediocre on a south swell, but excellent on a west or northwest swell.

The mystery of wave formation, wave quality, and wave forecasting has become a specialized science involving swell vigor, swell direction, swell clarity (whether or not it's been crosscut by secondary swells), nearshore bathymetry (the topographic features of the ocean floor, including reefs, points, and sandbars), tide, and local wind conditions. As with all weather-related science, however, the contributing elements can be altered, skewed, amplified, or subordinated. Surf forecasting continues to improve year by year, but wave-related permutations as of 2017 remain incalculable, while the final outcome—a breaking wave—remains breathtaking.

 (1964), by American oceanographer Willard Bascom, was the first book surfers read to gain a technical understanding of swell formation and wave/coastline interaction. 

Surf Science: An Introduction to Waves for Surfing

, by big-wave surfer and oceanographer Tony Butt, was published in 2002.

waves and wave formation

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