Watch a wave roll toward shore and it looks as though water is traveling across the sea. It is not. Waves carry energy, not water. As energy passes through, the water moves in a circle rather than traveling with it — and a wave with nothing in its way can cross an entire ocean basin.
Wind waves
Most waves are made by the wind. As it blows across the surface of an ocean or lake, friction between wind and water keeps disturbing the surface and builds a wave crest. These wind-driven, or surface, waves are found everywhere, in the open ocean and along the coast.
Dangerous waves
Some waves are far more hazardous:
| Wave | Cause | What it does |
|---|---|---|
| Storm surge | the strong winds and pressure of severe storms such as hurricanes | a series of long waves that form far offshore in deep water and grow as they near land |
| Tsunami | underwater disturbances that displace a lot of water quickly — earthquakes, landslides, volcanic eruptions | very long waves |
Neither looks like a wave curling onto the beach. They roll ashore like a massive rise in sea level, and they can reach far inland.
Tides are waves too
The gravitational pull of the sun and moon on the Earth also makes waves: the tides, which is why they can properly be called tidal waves. It is a common misconception that a tidal wave is a tsunami. Tsunamis have nothing to do with the tides, and can strike at any stage of the tide.
Sources
Based on "Why does the ocean have waves?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
许可协议： CC0 1.0（公有领域） · 改编自 oceanservice.noaa.gov
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