Periglacial resurfacing of hillslopes and channels with large boulders in the Virginia Appalachians

Abstract

AbstractLarge, resistant, quartz‐rich boulders deposited on hillslopes and in channels armour the landscape, trap sediment and influence hillslope angle and erodibility. In the Virginia Appalachians, such boulders are a significant component of hillslopes and channels. Establishing the timing of and processes responsible for bedrock fracture and boulder deposition is a critical piece of understanding the landscape as a system. In this study, we use cosmogenic 10Be exposure dating to resolve the timing of boulder deposition at three sites in the Virginia Valley and Ridge province: Gap Mountain, Brush Mountain and Little Stony Creek, and at one site in the Virginia Blue Ridge: Devil's Marbleyard. The correlation between measured boulder exposure ages (101.7 ± 6.9 ka to 10.8 ± 0.8 ka; n = 23) and the Wisconsin Glacial Stage and subsequent Laurentide Ice Sheet (LIS) deglaciation (~115–11.7 ka) suggests a periglacial origin for deposition of large hillslope and channel boulders in the Virginia Appalachians. The lack of boulder exposure ages corresponding to the Last Interglacial Stage or following Wisconsin LIS retreat suggests interglacial non‐deposition and stability. The absence of exposure ages from the penultimate Illinoian or older Quaternary Glacial Stages suggests that periglacial hillslope processes allow the landscape to be resurfaced with large boulders during each return to cold climate conditions. This cyclic resurfacing of hillslopes and channels is an example of how climatic oscillations insert disequilibrium into the landscape cycle and contributes to our appreciation of the timescales over which contemporary climate change may impact boulder dominated landscapes in rapidly warming alpine and arctic environments.