When a wave first forms in wind-blown water, it is called a sea. When it has left the storm area and is traveling across calm water, it is a "swell." When it reaches land and breaks, it is "surf."
The height of a storm wave, or sea, depends on violence of the wind, length of time the storm lasts, and extent of open water over which the storm rages. Most seas are only 5 to 12 feet high, but a two-day storm may produce 20-foot waves. Even 50-foot waves have been reported.
Each drop of water in a wave moves in a circular pattern, as if on a wheel. For a drop near the surface this circle is the height of the wave; deeper down the circle is smaller. Any one drop of water moves ahead at only 1 to 2 percent of the speed of the wave. At about 600 feet or more below the surface, the sea is alwavs calm.
Swells travel under their own momentum across wide areas of windless water. They are low, widely spaced, and fast-moving. They keep traveling in an orderly pattern to far-distant shores. As they travel, their height lessens, the spacing between waves lengthens, and their speed increases. Eventually a swell may travel faster than the wind that set it in motion.
When it nears a shore, the wave "feels bottom." Slowed by friction against the sea bottom, it rises from a low swell to a narrow, steep crest. The crest hurries forward faster than the slowed-down wave. Breaking into foam, it tumbles forward in a burst of fury onto the sand.
Sea Waves
