INFLUENCING FACTORS 145 



FACTORS THAT HINDER THE DEVELOPMENT OF SURF 

 OR THAT TEND TO INTERRUPT IT 



Ledges, shoals, and islands. — The types of surf just described are 

 those that develop where the bottom is comparatively smooth, as it 

 usually is off sandy beaches and off rocky coasts in many parts of the 

 world. But the development of breakers may be interrupted more or 

 less, in regions where the bottom is strewn with large boulders, or is 

 interspersed by submerged reefs. The latter, if rising near enough 

 to the surface for the waves to break over them are especially effective 

 in this respect, as described on page 132. And small islands scattered 

 within a bay, or at its mouth, provide still better protection. Thus the 

 surf breaks heavily at the mouth of Casco Bay on the coast of Maine, 

 during southerly and southeasterly storms (also during calms if a 

 swell is running), but the islands farther in protect the inner parts 

 of the bay to such an extent that its head is free from surf of any 

 size, at all times. And many other examples of this same sort might 

 be cited. 



The effects of bars near the coast have been discussed already (p. 

 132). Deeper and more extensive shoals farther offshore, such as the 

 great fishing banks of the North Atlantic, may also interfere with 

 the advance of ocean waves to some small extent. The effect of 

 Georges Bank, for example, crowned by the much shallower Georges 

 Shoal, with the tidal currents that run around and across it, so 

 hinders really long swells from the open ocean that these seldom 

 reach the western shores of the Gulf of Maine, though the distance 

 from the bank in to the shore is enough for a heavy surf to develop 

 there during onshore gales, or when storms pass by to seaward. And 

 Nantucket Shoals, which is shallower than Georges Bank, protects 

 Martha's Vineyard island rather more effectively from storm waves 

 coming from eastward, though leaving it open to waves from the 

 southward and southwestward. 



Tidal currents. — Oncoming waves that meet a contrary current, 

 while they are still some distance out from the land, or one transverse 

 to their own line of advance, may either be caused to break far out, 

 or be deformed in some other way, so that the shore line where they 

 would otherwise develop into breakers may be protected, more or less, 

 from surf, at least until the tide changes. 



For example, waves from offshore are so combatted by the swift 

 and confused tidal currents at the mouth of the Bay of Fundy, which 

 is some 30 miles across and wide open to seas from anywhere between 

 southwest and southeast, that surf developing up the bay is largely 

 of local origin. And the protection from the waves of southwest 

 storms that the southern coasts of the Shetland Islands receive in this 



