Estimating Bedrock Fracture Density of the Juneau Icefield, AK, to Inform Glacial Erosion Models

• Main Author: Rand, Colby
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2020
• Subjects: geomorphology; glaciology; glacial erosion; fracture density; glacial geology; Earth Sciences; Juneau Icefield; glacier; glaciers; Tidewater; Alaska
• Online Access: https://digitalcommons.library.umaine.edu/honors/610; https://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=1609&context=honors

Understanding glacial erosion rates is important because debris eroded by a glacier can impact glacier flow speeds, protect tidewater glaciers from rapid retreat, and impact the productivity of marine ecosystems. Traditionally, glacial erosion models rely on a rock’s inherent “erodibility”, typically presented as a constant, to predict how much debris will be eroded by the glacier. However, the erodibility of bedrock varies spatially as a function of its fracture density, fracture orientation, and lithology, so the notion of applying a constant erodibility term to a whole field site does not fully capture the actual bedrock dynamics of the system. In this work, I present a novel approach to quantify bedrock fracture density and orientation through the generation of a 3D Structure from Motion (SfM) model and the application of a series of machine learning algorithms. To test this approach, I quantified the fracture density of a glacial bedrock nunatak in the Juneau Icefield of Southeast (SE) Alaska. The spatial variation in fracture density across this nunatak was found to be highly variable. Bedrock in the SE region of this field site showed a relatively high fracture density (>20% fractured), whereas the central region of this field site showed a relatively low fracture density (0-10% fractured). Fracture orientations were shown to have a bimodal distribution, with the most common fracture orientations being approximately 0 and ± 90 degrees. This fracture density methodology and associated results can applied across the Juneau Icefield and other glacier systems to improve glacial bedrock erosion models.