128 



CHAKACTKK OF SURF 



the danger of landing if they are mflre than a few feel high. A very 

 striking example of the geometric nature of the patterns that are 

 produced on shelving beaches in this way. when small breakers come 

 together from different directions is pictured in figure 31. A current 

 (tidal or other) flowing against the wind will also tend to cause waves 

 to break in water deeper than would otherwise be the case, as illus- 

 trated by the aerial photograph reproduced in figure 32, for when a 

 wave meets an opposing current it is not only steepened, but its height 

 is increased as described on p. 53. A strong current may, in fact, be 

 as effective as a shoal or bar in causing large breakers to develop well 



Figube 31. — Geometric pattern produced by low breakers crossing eacli other 

 from different directions on the English coast. (After Cornish, courtesy of 

 Macniillan Co. and Cambridge University Press.) 



out from the land. The frequent reports of breakers over deeply sub- 

 merged banks, or along the slopes of such, are thus explained, for 

 example, along the Newfoundland Banks, off Ireland, and at the mouth 

 of the English Channel where the depth is something like 100- fathoms. 

 "Waves have also been reported as breaking in deeper water, if 

 running in over a steeply sloping bottom, than is usual off more gently 

 sloping beaches. The ratio of breaking depth to height of wave in 

 calm weather has been described, for example, as twice as large over 

 a 1 in 12 slope as a 1 in 100 slope at St. Augustine, Florida (Gaillard, 

 1904, p. 120) . On the other hand, the results of laboratory experiments 

 on a rather limited range of slopes do not support the view that the 

 steepness of the slope of the bottom has any great importance in this 



