The Making Of A Dune 



By Nancy Davis 



For some folks, dunes are little 

 more than piles of sand they cross to 

 reach the beach. 



Sunbathers trample them. Surf 

 fishermen plow through them in 

 four-wheel drives. And some proper- 

 ty owners don't appreciate the ser- 

 vices they provide. 



Sometimes it seems only artists and 

 photographers take notice of them. 



But sand dunes are much more 

 than pretty backdrops for paintings 

 and pictures. They provide a front 

 line of defense against the power of 

 ocean winds and waves. 



"Dunes are an integral part of a 

 barrier island's ability to maintain 

 itself,' ' says Sea Grant researcher 

 John Wells. 



"The most important thing about 

 a dune is that it's a natural buffer to 

 storm waves and an essential compo- 

 nent in the sand-sharing system," 

 says Wells, a coastal marine biologist 

 at the University of North Carolina 

 Institute of Marine Sciences. 



But in their role of island protector, 

 dunes take a terrible beating. Winds 

 and waves pound them. And occa- 

 sionally, storms sweep them away. 



But even though one dune disap- 

 pears, eventually another mound of 

 sand will take its place. 



The continual waxing and waning 

 of a sand dune is part of a natural 

 process, Wells says. 



He describes a dune as a reservoir 

 of sand. During storms, waves may 

 carry part of the sand in the reser- 

 voir a short distance offshore. There, 

 the sand may form sand bars that 

 lessen wave action. 



Eventually, the sea's natural wave 

 action will deposit some of that sand 

 back on the beach where it will be 

 available as building material for 

 another dune. 



If you've ever felt the twinge of 

 fine grains of sand blasting your 

 ankles as you walk along the beach, 

 you've witnessed a dune under con- 

 struction, says Sea Grant coastal 

 engineer Spencer Rogers. 



' All it takes to build a sand dune 

 is windblown sand and something to 

 trap it," Rogers says. "And all it 

 takes to get it to fall out of the breeze 

 is something near the surface to slow 

 the wind velocity' ' 



The sun and winds blowing off 

 the ocean dry tiny grains of sand on 

 the beach. The lighter, finer grains 

 become airborne. 



The sand is whisked across the 

 beach, and wherever there's an 

 obstacle — a piece of driftwood, a 

 sand fence or beach grass — the wind 

 drops its load of sand. 



Eventually, the wind will deposit 

 enough sand to form a new dune. 



How long that takes is up to the 

 availability of sand and the speed 

 and direction of the wind, Wells says. 



The wind also controls the shape 

 of the dunes and whether there's a 

 single ridge or a series of dunes, 

 Wells says. 



By examining the dunes on a 

 beach, you can tell a lot about an 

 island, Wells says. In North Carolina, 

 islands that are oriented in an 

 east/west direction tend to be more 

 stable and have better developed 

 dunes than islands oriented 

 north/south. 



As an example, Wells points to the 

 differences in the dunes on Shackle- 

 ford Island, an east/west oriented 

 island, and Core Banks, with a 

 north/south orientation. 



The dunes on Core Banks are small 

 and poorly developed. But Shackle- 

 ford's dunes are high and stable. 



On the Outer Banks, you can see 

 evidence of another kind of dune 

 ridge. But this is the work of man. 



Before the 1930s, the dunes from 

 Currituck to Ocracoke probably were 

 much smaller, and during storms the 

 ocean frequently surged landward. 

 But the Civilian Conservation Corps 

 stabilized the dunes in a continuous 

 mound of sand. 



At Jockey's Ridge, you can see an 

 example of yet another kind of sand 

 dune. It's the East Coast's highest 

 dune, but it's not even on the beach. 



Jockey's Ridge was formed from 

 excess sand that has blown and 

 washed over the beach dunes. With 

 little vegetation on it, the dune con- 

 tinues to move. 



A dune similar to Jockey's Ridge is 

 the site of the Wright Brothers 

 Memorial. But that dune has been 

 stabilized with grasses, Rogers says. 



