SURF AROUND HEADLANDS 167 



more sheltered shore behind them. Shadow zones of this sort are 

 commonly to be seen in the lee of steep headlands in moderate weather, 

 as we have observed; they are also found in the lee of steep-walled 

 islets, and of ledges that rise from a comparatively level bottom where 

 the water is deeper than, say, twice the height of the waves at the 

 time. But they are largely or entirely obliterated in heavier weath- 

 er, because the waves are then so much longer that refraction alters 

 their lines of advance out in much deeper water. 



The precise interplay of factors that determines just how much 

 protection from surf may be expected behind a projecting corner of 

 the coast is thus as varied as are the shapes of coast lines, the angle 

 with the coast at which the waves may be advancing, and their sizes 

 and shapes. But the general picture that results from theory and 

 observation combined, is clear enough to allow the following generali- 

 zations : 



a. The more abrupt the alteration in the trend of the coast and the 

 greater, and the wider the angle between the oncoming waves and the 

 more protected stretch of shore, the more shelter one may expect there 

 from the surf, under a given condition of wind and weather. 



b. If the angle between the oncoming waves and the more sheltered 

 stretch of coast is much more than, say 100°, one can expect a very 

 abrupt decrease in the height of the breakers, within a very short 

 distance inward from the corner. 



c. The farther in one goes from the corner along the more protected 

 shore, the lower may one expect to find the breakers. 



The shelter afforded by a projection of the coast line is greater still 

 if its more protected side is broken by lesser headlands and by coves, 

 because these tend, further, to break down any rollers that may follow 

 in along the shore. 



If the alteration in the trend of the coast is not only abrupt, but 

 is through so wide an angle that the two sides of the promontory are 

 nearly parallel, one with the other, as is true of a narrow spit, or of a 

 breakwater, the inner side may be so fully protected that landing is 

 easy there, and out nearly to the extreme tip, even when a heavy 

 sea is running directly against the exposed side. And the inner ends 

 of the waves may not be refracted around sharply enough to touch 

 the inner shore at all, if the alteration in direction of the coast is 

 sufficiently abrupt and if the submarine slope is steep enough, as al- 

 ready remarked (p. 166). 



Enclosed harbors and lagoons that connect with the open sea 

 through narrow channels, as between pairs of spits, or between break- 

 waters — also the lagoons of coral atolls — are fully protected from 

 surf, no matter from what direction the waves may be coming, nor 

 how high they may be, for once the crests have passed through the 



