Detecting Landscape Response to Perturbations by Climate and Base Level in Central Pennsylvania Using In-Situ 10Be and 26Al

• Main Author: Denn, Alison R
• Format: Text
• Language: English
• Published: UVM ScholarWorks 2017
• Subjects: boulder field; boulder stream; cosmogenic; Hickory Run; Pennsylvania; periglacial; Geomorphology; Ice Sheet
• Online Access: https://scholarworks.uvm.edu/graddis/723; https://scholarworks.uvm.edu/context/graddis/article/1722/viewcontent/Denn_uvm_0243N_10538.pdf; https://scholarworks.uvm.edu/context/graddis/article/1722/filename/0/type/additional/viewcontent/HR_DR_Tables_032817.xlsx

The change of topography with time and the consequent structure of Earth's surface is dependent on the production and transport of weathered bedrock. I use measurements of in-situ cosmogenic 10Be to investigate erosion rates and exposure ages of boulders, streams, and hillslope sediments in central Pennsylvania, a landscape shaped by glacial/interglacial climate cycles and changes in base level. I measure rates of landscape change at three separate sites, Hickory Run boulder field, Young Womans Creek watershed, and Garner Run, a small upland catchment bounded by two ridgelines. Hickory Run Boulder field is the largest of its kind in the eastern United States. This enigmatic, 1-km-long field of boulders has been attributed to frost-induced processes during the last glacial maximum, when the Laurentide ice sheet margin was nearby. My isotopic data demonstrate that Hickory Run, and likely many other similar boulder fields in eastern North America are ancient, multigenerational features that have persisted over many glacial-interglacial cycles. These findings add nuance to the conventional view of periglaciation as a force that "wiped the slate clean" in the Appalachian Mountains -- in upland areas with resistant lithologies, I show that the landscape was reworked, but not reset by repeated periglaciation. Young Womans Creek is a 230 km2 drainage basin in the headwaters of the Appalachian Plateau physiographic province, where I investigate the role of non-equilibrium topography on the rates of erosion at a basin scale. Here, I use in-situ 10Be to understand the influence of fluvial incision into the landscape, contrasting erosion rates in undissected uplands with those in incised valleys. Erosion rates are positively correlated with slope, but correlate negatively with normalized channel steepness, ksn, and downstream distance. My results demonstrate the effects of lithology and base level on erosion rate are difficult to disentangle, and that when studied on a small scale, lithology exerts the strongest control ...