What are ocean waves?
Waves are disturbances that move through a medium such as air or water. In the case of most sea surface waves, the disturbance is wind and the medium is water. Wind generated waves are dependent on the force of the wind, the distance over which the wind blows, and how long it blows.
Gulf of Maine waves
Wave action in the Gulf of Maine has produced some unique features in the coastal areas. Wave-driven movement of sand and gravel has created tombolos: for example, beaches or sandbars that join islands in Penobscot Bay. Waves have moved sand along the beaches and formed spits, like Cape Cod, while eroding other areas, like the outer cliffs of the Cape. Wave action has also sculpted many Gulf of Maine beaches on sandy river deltas.
Waves are usually described by their wave height and wavelength. Wave height is the distance from the trough to the crest of the wave. Wavelength is the distance between the corresponding points on successive waves, for example from trough to trough, or from crest to crest. Every hour, GoMOOS buoys measure the surface wave heights for 8.5 minutes. These wave heights are then averaged to obtain that hour's reading in feet and meters.
Wave height generally increases with wind speed. Thus wave height, which is easier to estimate by eye, is often used to describe sea state. The Beaufort Wind Scale is one way this information is synthesized. Using wave height and the Beaufort Scale, you can estimate wind speed. For example, wave heights between 15 and 20 feet are associated with near gale conditions (i.e., wind speeds of about 30 knots): time to "batten down the hatches!" Wave heights can range from 0 feet (i.e., a smooth, mirror-like sea) to over 45 feet during hurricanes.
Waves are a powerful source of energy and can significantly impact coastal zone patterns by moving sand and gravel. Waves can even smash and tear objects that are caught between a wave and the shore.
In coastal zones, waves can create special habitats by spraying water beyond the normal tidal range: inhabitants of these areas are called "spray zone" organisms. Crabs, snails, barnacles, and lichens are common in "spray zone" colonies.
Beyond the Gulf: What are wave heights on a global scale?
From the satellite images at right, it is clear that wave height and wind speed are correlated. The greatest wave heights (shown as red) are seen in locations with the highest wind speeds: this is evident in the Southern Ocean near Antarctica. Notice that the shortest wave heights (and the slowest wind speeds) are generally found around the equator. These data, acquired by NASA's TOPEX/Poseidon satellite, are averaged over 10 days in October 1993.
Seismic disturbances can also produce waves in the ocean, including underwater earthquakes or avalanches. These waves are called "tsunamis," which is the Japanese word for "harbor wave." (Tsunamis are sometimes called "tidal waves," which is incorrect as they have nothing to do with tides.) The wavelengths of tsunamis typically exceed 200 kilometers. In deep oceans, the seismic waves are unnoticeable; however, when a tsunami approaches shallow water, it can reach as high as 100 feet or more.
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- deCharon, A., and M. Sieracki. (1999). Ship Mates: Explore the Gulf of Maine as Oceanographers Do. URL: http://www.bigelow.org/shipmates.
- NOAA/National Weather Service. (2002). Storm prediction center. URL: http://www.spc.noaa.gov/
- Nybakken, J. W. (1993). Marine Biology - An Ecological Approach, 3rd Edition. Harper Collins.
- Thurman, H. V. (1991). Introductory Oceanography, 7th Edition. Macmillan Publishing.
- TOPEX/Poseidon Project. (2002). Ocean surface topography from space. URL: http://sealevel.jpl.nasa.gov/
- University of South Florida Distance and Technology Mediated Learning. (1998). Project Oceanography Spring Series. URL: http://www.marine.usf.edu/pjocean/
