56 SMITH 



SUMMARY OF DISCUSSION 



Much of the discussion concerned sand dunes as indicators of wind direction. 



It was pointed out that if there were very strong, persistent offshore winds, there would 

 be few dunes. Dunes are built only where the onshore winds are more vigorous than offshore 

 winds, unless there is enough vegetation to prevent the offshore winds from contacting the sand. 

 Wherever blowouts rise high enough to top the vegetation, they are exposed to winds from both 

 directions. If blowouts are extended in a landward direction, there cannot be very effective 

 winds from that side. Some types of dunes are much better recorders of wind directions than 

 others, some give only a very rough indication or net resultant. 



Mainly, the dunes indicate the direction of winds strong enough to move the sand. It 

 might be possible that a wind from one direction would be considered the prevailing wind in 

 terms of time, but might not be strong enough actually to move the sand, while an occasional 

 wind from another direction might be above the critical velocity necessary to move sand. In 

 such a case, the direction indicated by the dunes would be that of the occasional winds. The 

 only winds of significance in dune building are those strong enough to move the sands. 



In less arid regions some consideration must be given to the time of year when the strong 

 winds blow in reference to the amount of evaporation and rain. Although it has been reported 

 that even moist dune sands can be blown by winds of sufficient velocity, ordinarily sand is 

 moved by winds free from a great amount of precipitation. 



