A LIDAR-BASED STUDY OF THE RELATIONSHIP BETWEEN CAROLINA BAYS AND COEVAL SAND DUNES

The Carolina Bays are shallow, elliptical depressions found in the US coastal plain between northern Florida and New Jersey but are most common in the Carolinas. It is estimated that as many as 500,000 of these features exist and many hypotheses have been proposed to explain their origin, including meteorite or comet impacts, solution depressions, eolian blowouts, and fish nests. An analysis of the bays and coeval parabolic dunes near the Cape Fear River in North Carolina using recently acquired LIDAR data indicate a correlation between bay orientation and wind direction that fits with the idea, first proposed by Cooke (1940), that the wind creates gyroscopic eddies that erode the shallow water-filled bays into elliptical shapes whose minor axes should be parallel to the wind direction.

The study area was divided up into domains based on the relative ages of terraces of the Cape Fear River to detect temporal and spatial differences in prevailing wind directions. Bay shape is fairly constant and independent of surface area, with an average eccentricity of 0.8 and little difference among domains. Paleowind directions, as indicated by parabolic dunes for each domain, range from 55° ± 2° to 73° ± 3° and are on average more easterly than the average orientations of the bays minor axes, which range from 41° ± 2° to 52° ± 7°. This slightly more easterly wind direction could explain the common occurrence of sand rims on the southeastern shores of the bays in both this study area and in published accounts from Georgia and South Carolina. Bays located adjacent to dunes (most commonly the dunes are near the northeast rim of the bay) are almost always oriented with their minor axis parallel to the wind direction indicated by the dunes, which fits the gyroscopic eddy hypothesis. In some clusters of both large and small bays, the minor axes of the smaller bays are parallel to the wind direction indicated by the adjacent parabolic dunes. The minor axes of the larger bays, however, are commonly oriented closer to the wind directions indicated by dunes on nearby, but older terraces. This relationship suggests that the larger bays acquired their elliptical shapes earlier than the nearby smaller bays.