Modeling the Evolution of Basal Sliding Rates on the Athabasca Glacier

Abstract:

The evolution of glacier basal sliding rates on decadal timescales remains poorly constrained. The Athabasca Glacier provides an ideal study site for observing and modeling basal sliding changes in response to the past 50 years of climate forcing. Borehole inclinometry studies from the 1960s provide a baseline dataset of the glacier’s internal deformation before > 60 m of thinning and half a kilometer of terminus retreat. Our ongoing study aims to collect a contemporary suite of datasets for the same glacier which will then be used to inform our modeling efforts. These in situ measurements include: GPR-derived bed topography, borehole deformation rates from three-axis tilt meters, basal water pressure, and GPS-derived surface velocity fields. We utilize inverse methods to determine the rate and spatial distribution of basal motion from observations of englacial strain rate profiles and surface velocity along multiple transects of the Athabasca Glacier. Here we present preliminary results from a two-dimensional (map plane) vertically integrated ice flow model, based on the open-source finite element package icepack to calculate internal stress and strain rate fields. We perform a sensitivity analysis using synthetic borehole tilt profiles along transects of the Athabasca Glacier to investigate the impact of different borehole locations on the derived velocity field. We use digitized borehole tilt data from Raymond (1971) as a model target to determine the initial stress state of Athabasca from several decades ago. In the future, we plan to assimilate borehole tilt data collected in the 2021 field season to reproduce the modern dynamic state. These data will provide a unique constraint on how the distribution and magnitude of basal motion evolve as the glacier’s geometry and hydraulics respond to modern climate change.