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| Thursday, 30 December 2004 |
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Tidal wave or tsunami? PARIS, Wednesday (AFP) The giant, deadly waves of seawater that crashed through coastal towns in Asia and parts of east Africa last weekend are commonly called tidal waves, but that term is not strictly correct, say scientists, who prefer the word "tsunami". The walls of water that smashed into Sri Lanka, India, Indonesia, Thailand and other countries in the region were caused by a massive shift of tectonic plates under the Indian Ocean - a sea quake - and were not caused by the moon's pull, which creates tidal phenomena, they noted. Tsunami, a word borrowed from Japan, where earthquakes are common, is considered more apt - even though it literally means "harbour wave" and the fury unleashed last Sunday was more far more widespread than that. The US Geological Survey, which forms part of the international Tsunami Warning System for the Pacific Ocean, defines a tsunami as "a wave or series of waves that are generated by a sudden disturbance that displaces water." It adds that they are "typically caused by earthquakes and landslides in coastal regions." The term "tidal wave," it says, "is a misnomer.... The impact of a tsunami upon a coastline is partially dependent upon the tidal level at the time it strikes, but its generation is unrelated to ocean tides." The Australian Academy of Science agrees, calling the term tidal wave "inaccurate". The US National Aeronautics and Space Administration (NASA) says on an explanatory webpage: "The phenomenon we call a tsunami is a series of waves of extremely long wavelength and period generated in a body of water by an impulsive disturbance that displaces the water. "Although tsunamis are often referred to as 'tidal waves' by English-speaking people, they are not caused by the tides and are unrelated to them." |
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