140 CHARACTER OF SURF 



advances shoreward, as described on page 115, while still a third may 

 do so intermittently, so that it alone may be responsible for several 

 lines of breakers, before it is extinguished finally on the beach. 



The sidewise extent of the individual crests also enters into the 

 situation, for when this is wide (as it is for swells), the breakers will 

 extend correspondingly far sidewise, and the number of lines of surf 

 will be more constant than when the crests are narrow laterally, as 

 they are if the waves are younger. In the latter case, patches of surf 

 may alternate irregularly with lanes or patches of unbroken water, 

 so that the number of lines of breakers is changing constantly. The 

 breakers caused by storm seas therefore vary widely in size, one from 

 the next ; they are also very irregular in their surface contours. And 

 they break at different times along different fronts. Added to this, 

 storm seas that are already breaking offshore may continue to do so 

 with increasing violence, as they advance into shoaling water, causing 

 a confused zone of heavy surf perhaps hundreds of yards wide, so 

 varied in pattern and so constantly changing that no definite number 

 of lines of breakers can be counted, even along a narrow front. In- 

 deed, there may be no sharp line of transition, during an onshore 

 storm, between the breaking of the seas offshore, that is caused by the 

 wind alone, and the surf zone that develops because of the shoaling 

 bottom. 



The lines of breakers that are caused by a swell are much more 

 regular, not only in number and in their distances out from the land, 

 but also in the sidewise extent of each crest, while the outermost line 

 of surf breaks fairly regularly along a comparatively narrow depth 

 zone of the bottom. Further, the waves usually are not breaking at 

 all to seaward of the outermost line of surf. Under these circum- 

 stances, the crests often extend far sidewise — perhaps as much as 

 1,500 yards. 



The angle at which the bottom slopes also plays a very important 

 part in determining how many lines of breakers there will be. The 

 one extreme in this respect is exemplified by a steep headland or 

 breakwater, or a very steep beach, against which the surf may break in 

 a single line as described above (p. 138), irrespective of the initial 

 shapes of the waves. Gently sloping foreshores exemplify the other 

 extreme, where there may be many lines of breakers (fig. 35), for 

 succeeding waves will break before preceding ones have reached the 

 shore. And the situation may differ widely in this respect on a given 

 beach, at different stages of the tide, for the slope is much more gentle 

 below low-water mark than it is between low-water mark and high- 

 water mark in many localities. Under these conditions there may be 

 anywhere from only one or two lines of breakers to as many as five or 



