HURRICANES 



clay up to 6 inches thick; they are 

 permanent additions to the marsh 

 deposits. 



Some Generalizations 



The three specific examples given 

 here justify several generalizations 

 that can be substantiated by many 

 other case histories: 



1. Catastrophic as they are from 

 human, biological, and eco- 

 nomic standpoints, in most in- 

 stances hurricanes result in 

 only minor and ephemeral geo- 

 morphic changes, and these are 

 confined to coasts. 



2. A coast where durable rock is 

 exposed to the violence of 

 storm attack (Mauritius ex- 

 ample) suffers negligible physi- 

 cal change. 



3. A coast flanked by deep water 

 close to the shore (Plum Island 

 and Mauritius examples) is af- 

 fected mainly by high seas. 

 Unconsolidated materials such 

 as beaches and sand dunes ex- 

 perience abrupt changes, but 

 these last for only short periods 

 of time. 



4. A coast flanked by a broad, 

 gently inclined continental 

 shelf, with a long fetch across 

 shallow bottoms, suffers 

 changes associated with flood- 

 ing (Louisiana example). 



Hurricane Carol (Mauritius) 

 brought a storm surge that registered 

 only about 33 inches above expected 

 level on the tide gauge at Port Louis. 

 The island is surrounded by deep 

 water. Hurricane winds generated 

 high seas along all shores, however, 

 and it was these that accounted for 

 physical and biological changes. Much 

 the same experience was associated 

 with another Hurricane Carol (Plum 

 Island). At Plum Island, the 10- 

 fathom isobath hugs the shore 

 closely, and a depth of 50 fathoms 



lies only 6 miles out. In contrast, in 

 southern Louisiana the 10-fathom 

 isobath lies about 43 miles from the 

 shore, and the 50-fathom depth lies 

 some 118 miles out. Hurricane surges 

 are low over open ocean and are not 

 significant aboard ship, but they rise 

 to 15 feet or more when their rate of 

 forward advance is reduced by shear 

 or friction, creating greater and 

 greater turbulence and more vigorous 

 internal waves as they travel across 

 wide, gently rising bottoms, especially 

 at shallow depth. 



Although not much coastal change 

 ordinarily occurs when water attains 

 a depth of more than 5 fathoms 

 within a short distance, too much de- 

 pendence should not be attached to 

 this relationship. With gently in- 

 clined bottoms, offshore surges may 

 grow to proportions that create ex- 

 tensive flooding. These surges con- 

 tinue for long distances, both across 

 shallow bottoms and adjacent coastal 

 lowlands. Even in the extensive and 

 shallow area east of New Orleans, 

 local inhabitants identify channels in 

 the marsh and cuts across linear 

 islands as having resulted from hur- 

 ricanes in 1915 and 1925. A popular 

 resort on Isle Derniere, south of New 

 Orleans and landward about 27 miles 

 from the 10-fathom isobath, was 

 wiped out with tragic consequences 

 in 1856, when the position of the 

 low sandy spit on which it was built 

 was shifted westward. 



Hurricane Protection: 

 Problems and Possibilities 



An individual hurricane arrives as 

 a possibly catastrophic event, one 

 that is likely to be considered unique 

 in the minds of people affected. The 

 fact is, however, that the storm is but 

 one of a recurring series that reach 

 the region at highly irregular inter- 

 vals. Hurricane arrivals are as un- 

 certain as those of impressive earth- 

 quakes. Although the present state 

 of the art does not justify exact fore- 

 casts concerning either, except for 

 short terms in the case of hurricanes, 



both meteorologists and seismologists 

 recognize that there are definite hur- 

 ricane- and earthquake-prone regions. 

 Eventually, it may be possible to 

 educate people living in them to 

 recognize that they must protect 

 themselves against potential catas- 

 trophes. 



Most hurricanes reaching the 

 United States originate either be- 

 tween the Azores and Cape Verde 

 Islands or else in the Caribbean. 

 There is no evidence that any origi- 

 nate within 6" of the equator. In 

 most cases they are first identified 

 in latitudes between 10 and 20° 

 north. The shores of the Gulf and 

 Atlantic coasts, from Brownsville, 

 Texas, to Lubec, Maine, are every- 

 where vulnerable to hurricane attack. 

 Tracks are particularly concentrated 

 near Puerto Rico and Florida, but 

 extreme damage has occurred around 

 all parts of the Gulf of Mexico and 

 up the Atlantic seaboard at least as 

 far as Cape Cod. 



Defense against events such as 

 hurricanes, tornadoes, earthquakes, 

 and destructive volcanic activity is 

 most effective in places where dis- 

 aster strikes most frequently. Cy- 

 clone cellers have undoubtedly saved 

 many lives in the American Middle 

 West. The Japanese have done well 

 in designing structures that withstand 

 intense earthquake tremors. 



Practically all serious damage re- 

 sulting from hurricanes is caused by 

 human mistakes. Protective beaches 

 are mined for sand, shell, or gravel. 

 Sand dunes, among nature's most 

 effective coastal protectors, are bull- 

 dozed away to level land for building 

 sites or even to enhance seascape 

 views. A trip along any part of the 

 Atlantic coast between Florida and 

 Cape Cod soon after a hurricane will 

 demonstrate gross variations in dam- 

 age, depending on whether beaches 

 or dunes had been altered seriously. 

 Cities and towns suffer most, not only 

 because they are concentrations of 

 people and buildings but also from 

 the fact that they have introduced 



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