49. What causes "tidal waves"? 



"Tidal waves" are not caused by the tides, but by movement of the 

 ocean floor. Their proper name is tsunami, a word of Japanese origin. 

 They are also commonly called seismic sea waves. 



Submarine earthquakes, landslides, or volcanic eruptions create tsu- 

 namis; a submarine disturbance may produce three or four waves with a 

 wave length (crest to crest) greater than 3 miles, although their height 

 over the open ocean may be only 1 foot. Speed of advance can exceed 

 500 miles an hour. As the waves approach shore, they are slowed and 

 the water behind piles up to tremendously destructive heights. 



Cowan, Robert C. 



Frontiers of the Sea, Doubleday and Company, 1960. 

 Gaskell, T. F. 



World Beneath the Oceans, American Museum of Natural History, 



1964. 

 Stewart, Harris B., Jr. 



Deep Challenge, Van Nostrand, 1966, 



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