PROFILES AND SURFACE CONTOURS 



45 



short storm waves are very much steeper than those of relatively 

 longer ones. In one case that has been frequently reproduced ( fig. 12 ) , 

 the difference in level between the highest and the lowest points was 

 between 26 and 27 feet in a horizontal distance of only about 190 feet, 

 or a ratio of length to height of only a very little more than 7:1. This 

 crest was thus on the point of breaking, and waves of this shape are 

 very commonly seen in stormy weather. 



10 



5 

 O 



io 



5 

 O 



t 



W 30 



Z 25 



12 20 



O 



Z 15 I— 



III 



(E 



III 



t- O h- 

 I 

 



bj 25 

 I 

 20 



15 



10 



5 

 O 



O lOO 200 300 400 500 



HORIZONTAL DISTANCES IN FEET 



Figure 12. — Profiles of waves of different degrees of steepness, based on stereo- 

 photogrammetric pictures. The vertical scale is five times the horizontal 

 scale. (Adapted from Schumacher.) 



Instability of this same sort can also develop in very small waves 

 as well as in large, whenever the wave is growing rapidly in height, 

 as is usually the case with a rising wind of any considerable strength. 

 The "whitecaps" that develop when a brisk breeze blows up are 

 familiar examples. The seas may continue to break even after they 

 have ceased to increase in height, if the wind continues strong, because 

 the pressure of a high wind is so much stronger on the back of the 

 crest (its windward side) than on its front (lee side) that its crest is 



