Outcrop-scale Estimates of Fracture Density Using Structure from Motion on the Juneau Icefield

Traditionally, regional-scale glacial erosion models rely on a homogenous bedrock cohesion estimate. However, the strength of bedrock varies spatially, and the notion of applying a constant cohesion to a whole field site does not fully capture the actual dynamics of the system. The bedrock's cohesion is partially controlled by its fracture density. Measuring the fracture density of recently exposed bedrock gives the best available approximation for the fracture density under a glacier, hereby reflecting the approximate cohesion of the bedrock. Although we cannot calculate the exact erodability of the bedrock, we could gain the lower bound of local erodability through field work, helping to improve and quantify bedrock erosion rates in other glacial erosion models. We quantified the fracture densities of exposed bedrock on the Juneau Icefield in SE Alaska/NW British Columbia using a Structure from Motion model based on drone images. The Juneau Icefield is used as a control in this study of fast-eroding glacial environments because it is not influenced by the tectonics of the Fairweather Fault Zone. The fracture density data will improve glacial erosion models, including outputs using the last glacial cycle of the University of Maine Ice Sheet Model (UMISM).