As waves sweep in toward the coast and enter 

 stiatlow water, ttiey slow down and curve into 

 ttie stiape of tiie bay tliey may be entering. 

 Tiie photograpti tiere sliows waves breathing on 

 the beach at Angus Point, Ireland. 



Since the last ice age Scotland has been 

 slowly rising out of the sea. A raised beach 

 partly obscured by sand can be seen in the 

 middle background of this photograph of the 

 Sands at Gairloch, western Scotland. 



the bottom, the movement of water within each wave changes 

 pattern. As the wave form begins to lose its symmetry on the sur- 

 face, the circular motion of water making up the wave becomes 

 elliptical, and along the bottom the water moves to and fro. The 

 water directly under each wave crest moves forward toward the 

 beach, accelerating as each crest becomes shorter and steeper; but 

 under each trough there is a slower, seaward movement of water 

 before the wave breaks. It is the bottom movement of the water 

 beneath the wave crest that pushes sand and gravel-like material 

 called shingle up toward the coast and high onto a beach. Shingle, 

 easy for the water to move, is usually foiind near the top of a mixed 

 beach. 



If we look at an aerial photograph of long waves moving in 

 toward the coast it is easy to see that they bend around and become 

 nearly parallel to the shore. This is because the waves travel more 

 slowly where the water becomes shallower, so that part of a wave 

 entering shallow water first gets held back, while the parts still in 

 deeper water sweep forward faster. This bending of the wave 

 crests, called wave refraction, concentrates the energy of waves on 

 certain parts of the coast, particularly on promontories and where 

 land ridges extend into the sea. The waves tend to build higher 

 here and set up the longshore currents that run along the coast to 

 more sheltered areas where the waves are lower. As a result, an 

 excess of water bmlds up and tries to escape seaward, as a rip 

 current, through the breakers. Longshore currents may also be set 

 up by waves approaching the shore obliquely, especially when the 

 waves are short and, therefore, not seriously affected by refraction. 



The effects of the wind on coastal waves, and so on the coasts 

 themselves, can be destructive or constructive at the edge of the 

 sea. An onshore wind, by creating an undertow along the sea floor, 

 helps to make waves destructive, while an offshore wind has the 

 opposite effect. But waves are not the only force affecting the edge 

 of the sea, although they are the most important one. The tides, 

 described on page 214, also set up local currents that influence the 

 movement of material in the sea. Sandbanks, such as the Goodwin 



226 



