Paper No. 19-10
Presentation Time: 11:40 AM
THE CAROLINA BAYS OF RIDGE SPRING, SC
A narrow, sinuous terrace known locally as The Ridge forms a contiguous drainage divide arcing ~100 km from Augusta, GA, northeastward toward Columbia, SC. A new one-meter-resolution digital elevation map was crafted for the terrace using LiDAR data from the SC Department of Natural Resources, providing a crisp perspective of the surficial features present. From their lofty perch at ~200 m elevation, the low-relief terrain surrounding Ridge Spring, SC represent a surviving island of flat Cretaceous terrace that is being encroached upon by headward fluvial erosion. Edisto River basin headwaters are eating away the southeastern flank, while along the northwestern flank, tributaries of the upper Santee River drainage basin are collaborating with those of the Savanah River to remove the divide. Of the 45,000+ East Coast bays in the Carolina Bay Geospatial Survey, only 171 bays exist at elevations above 185 m. The Ridge Spring terrace is home to 160 of those high-elevation bays, making the assemblage unique in many ways. These bays maintain robust conformance to the archetype “baySouth” teardrop planform common to over 16,000 neighboring bays; their major axis range from 1.22 km down to 140 m, with a mean of 380 m; the orientations of that axis range from 148º to 165º, with a mean of 154º. The bays of Ridge Spring are visualized in LiDAR as basins recessed into a surrounding pediment (here, the terrace), exhibit no raised southeastern rim, and have no aeolian dune formations in their vicinity. The headward erosion has been dissecting the terrace since the time of bay formation, as the LiDAR elucidates a history of systematic bay destruction. Some clearly-defined bays have been penetrated by headward erosion, and are no longer hydraulically closed. Former closed-rim bays - recognizable by surviving rim fragments - have become mere “headwater basins”. At some point in the future the last vestiges of the terrace surface and the imbedded Carolina bays will be gone. How long will that take? These observations indicate that Carolina bays are not wispy, ephemeral shorelines, but rather represent the surficial expression of robust structures deeply rooted into the landscape. Ridge Spring represents an ideal locale to investigate the burial chronology of Cretaceous strata by surficial sands using Beryllium-10 cosmogenic exposure techniques.