g. California Current) which transport cold water to the tropics where this is heated and pushed back to the poles by the western streams. Consequently, ocean surface currents help the Sun energy spread from the equator to the poles ((http://science.hq.nasa.gov/oceans/physical/OSC.html).
Swells, breaking surf, tsunami
Swells may be defined as "a long series of ocean waves, generally produced by wind, and lasting after the wind has ceased" (http://en.wikipedia.org/wiki/Swell).They may be generated thousand of miles away from the beach by tropical storms or wind systems. Such a genesis explains their higher stability in direction and frequency, and the major attractiveness that they exert on surfers. Thus, swells are the so called wave trains which display considerable wavelength or period. This is a parameter measuring "the average length of time between each wave in a set" (http://en.wikipedia.org/wiki/Swell).For instance, the first waves in a swell might have 20 to 25 seconds, while the second group which might arrive 2 days later, could have a period of 17 seconds. The wavelength is the natural consequence of the energy invested by the wind into the ocean. A swell's strength to surpass obstacles depends on the Aeolian energy. Therefore, short-period swells, measuring up to 14 seconds, are fragile in front of winds or seas, while long-period swells, measuring over 14 seconds, prove to be more resistant (Collins, 2007).
The swell speed (in miles per hour) may be calculated as a product between the period (in seconds) and 1.75. Thus, at a 10-second period, the speed...
For example, a 20-second period swell will have a depth of 1024 feet (Collins, 2007).
Sometimes waves have the tendency to break when they encounter shallow waters, when two opposite systems meet or when winds become so strong that they are able to remove the wave top. Breaking waves are very dangerous because they can overturn boats and crush ships due to the impressive pressure of up to 50 or 100 kilopascals (4-9 short tons per square yard). Their main treat refers to the speed of the wave crest which is equal to that of the wave itself. Consequently, the base isn't capable of supporting the top and this failure results in wave breaking (http://seriesdrogue.com/coastguardreport/breaking_waves.htm).
Tsunamis occur where the sea floor undergoes severe deformations that vertically displace enormous amounts of water. Some of the causes responsible for this phenomenon may be earthquakes, meteorite impacts, eruptions, underwater explosion and so forth. Unlike surf swells, tsunamis display a huge energy that remains fairly constant, despite the great distance they travel. Moreover, they behave as shallow waters with an average speed of 400 to 500 mph and extremely long periods or wavelength. Therefore, tsunamis may not be even noticed by ships sailing in the open ocean. The striking effect is released when reaching
