Making Waves

Seawater is rarely still, it is usually moving in waves, tides or currents. Waves are caused by wind blowing across the surface of the ocean. The height of a wave is determined by the wind speed, the length of time the wind has been blowing, and the distance the wave has traveled over the ocean. The highest wave ever recorded had a height of 116 feet, 34 meters, although usually they are much smaller. Waves play a very important role in the shaping of coastlines. Water does not move along with the waves, instead it changes shape as a wave passes, moving in a roughly circular motion, rising towards a wave crest as it arrives and falling as it passes. This motion can be seen by watching a boat: the boat bobs up and down as the wave moves passed it, but does not move along with the waves. There is another type of ocean wave, which is not generated by the winds. These are called ‘tsunami’. They are also popularly called tidal waves. This name is quite wrong though, as they are not caused by tides. Tsunamis are due to earthquakes or the eruption of undersea volcanoes, which move a large amount of water rapidly, disturbing the sea’s surface, creating waves that travel away from the area of the earthquake or volcano. Tsunami’s travel at very high speeds, 470 miles per hour, 750 kilometers per hour. In the open ocean they cause little damage because their wave height is very low, usually less than 3.25 feet, one meter. In shallow water, they slow down and their height increases to 33 feet, 10 meters, or more, causing extensive damage when they hit a shore