The Bird in the Waterfall by Jerry Dennis and Glenn Wolff



W A V E S
Beyond the Wind
Jerry Dennis & Glenn Wolff

Swell waves travel beyond the wind, either leaving the area where it is blowing or continuing on after the wind has ceased. They are usually low and long -- with low wave heights and long wave lengths -- and follow each other at approximately the same distance. Such waves begin when sea waves "decay," their crests becoming lower and more rounded and symmetrical until they proceed as an orderly series of similarly sized waves. In outline, swells are shape much like a true sine curve, the classic wave of laboratory theory. It's an efficient shape: As long as they remain in deep water, swells can cross thousands of miles of ocean and lose very little energy. They are among the longest of all waves, not uncommonly measuring 1,000 feet from crest to crest and, on rare occasions, measuring as much as a mile. They are also faster than other waves. In the deep water of the open ocean they travel at 15 to 20 miles per hour, which allows them to pass through slower sea waves and organize themselves into clusters called trains. Such clusters eventually crash to shore as a succession of large breakers, perhaps contributing to the myth of the "ninth wave." Many people have believed that the ninth wave (or 10th or 3rd, depending on the place) is always the largest. An hour of observation on any beach should be enough to disprove the myth, though it lives on. Some waves are larger than others, true, but the disparity is caused because swells and sea waves sometimes pass into one another, combining their energy and producing random waves much larger than average.

The steepness of a wave never exceeds a 1:7 ratio of height to length.

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