ROLE OF HILLSLOPE AND GLACIAL PROCESSES IN FORMATION OF HIGH ELEVATION BOULDER FIELDS IN THE SOUTH-CENTRAL APPALACHIAN MOUNTAINS: AN INVESTIGATION OF THE DEVIL’S MARBLEYARD DEPOSIT, VIRGINIA

The Late Wisconsinan Stage of the Laurentide Ice Sheet in North America significantly modified the glaciated northern Appalachians. It also brought periglacial conditions to the southern Appalachians that notably affected the landscape. Throughout Pennsylvania, south of the glacial limits, the origin of features such as block fields and boulder streams have been attributed to periglacial processes, including freeze-thaw processes and frost shattering. Further to the south, the Devil’s Marbleyard boulder field, located within the South-Central Appalachians Blue Ridge physiographic region, shares similarities with other periglacial landscapes including elevation, boulder size range, and slope gradient of the deposit. High resolution topography based on structure-from-motion was obtained to generate 3D models of the deposit, from which remote measurements of over 200 boulders were used to determine the presence of size and orientation distribution trends in the deposit. Associated mapping of the deposit and in situ bedrock fractures was performed in order to determine the processes controlling emplacement mechanisms in the boulder field. Morphological trends, such as decreasing block size with decreasing elevation and increasing distance from source bedrock, and coincident orthogonal fracture systems, provide evidence for “flow-like boulder creep” mechanisms responsible for deposit emplacement. Cosmogenic radionuclide dating, performed at PRIME Lab at Purdue University, was used to constrain the timing of emplacement or remobilization of the boulder field to Pleistocene LGM ages ranging from 18.5 to 28.5 ka (n= 6). Morphological trends and cosmogenic data suggest the deposit origin is attributed to progressive stress and mechanical failure along joints and fractures combined with a translational down-slope slide, without the requirement, but possible imprint, of periglacial processes. This research is significant for understanding the influence of Pleistocene climate change and inferred periglacial processes on high ridges in the Appalachians, as well as erosional regimes of the southern Appalachian highlands. Together, these provide a baseline for understanding how the landscape will respond to future climate change and anthropogenic modification.