12 



PHYSICAL NATURE OF WIND WAVES 



HURRICANE OR "TIDAL" WAVES 



One other type of wind wave remains to be considered, namely, the 

 very high and long waves — distinct from swell — that sometimes pre- 

 cede or accompany a tropical hurricane; these have done enormous 

 damage along the coast, at great cost in human life in different parts 

 of the world on many occasions. 



The most characteristic feature of waves of this sort (often erro- 

 neously called "tidal waves") is that they inundate low coastal areas 



Figcke 4.— Submarine photograph showing ripple marks at the bottom of the 

 Gulf of Maine at a depth of 498 feet. (Photograph, courtesy of Dr. Maurice 

 Ewing, Woods Hole Oceanographie Institution.) 



that are not normally subject to overflow by the tides, sometimes to a 

 vertical height of as much as 40 feet, so suddenly and so overwhelm- 

 ingly at times that there is no escape. It has, in fact, been estimated 

 that such waves (they may come in trains of 2 or 3 or more) have 

 been responsible for more than three-fourths of all the loss of life 

 that has been caused by tropical hurricanes in one part of the world 

 or another. 



The wave that overwhelmed the city of Galveston, Tex., on Septem- 

 ber 8, 1900, at a cost of nearly 6,000 lives and of tens of millions 



