Ocean Waves and Tides

Winds that blow over the ocean create surface disturbances called waves. The greater the wind speed, the larger the wave. Waves 50 feet (15 m) high are not unusual during severe storms.

Surface waves are of two types: sea waves, choppy waves driven by the wind; and swell, uniform waves occurring in areas where there is no wind. After sea waves pass out of a windy area, they develop into swell.

Swell can travel a great distance from the area of the ocean where it originated. (As in all other types of wave motion, it is the disturbance, rather than any material substance, that travels.) The breakers and surf occurring near coastlines are formed from swell.

Waves that result from dislocations of the ocean floor are called tsunamis. These waves are long and can cause great destruction in coastal areas. They are sometimes called tidal waves, although they have no relation to tides.

In addition to currents and waves, a third important type of ocean-water movement is the tide. Tide is the alternate rising and falling of the ocean surface due to the gravitational pull of the moon and the sun. Gulfs, bays, and rivers connected with the open ocean are also subject to tides.