Ice velocity and basal motion evolution of mountain glaciers on multi-decadal to centennial timescales

Abstract

The surface velocity of a glacier or ice sheet consists of two components, viscous deformation throughout the ice column and basal motion comprised of sliding along the bed and the deformation of subglacial till. Changes in basal motion on multi-decadal to centennial timescales could result in either a positive or negative feedback which accelerates or delays ice mass loss rates. Most glacier systems maintain a relatively stable ice flux, while surge type glaciers are prone to large flow instabilities between their surging and quiescent phases. How fast and how much basal motion will change in response to higher temperatures is not well understood. In this dissertation, my coauthors and I utilized models, modern observations of ice deformation, and a 50-year-old baseline dataset from Athabasca Glacier, Alberta, Canada. We used recent field observations of Athabasca Glacier borehole deformation from tiltmeters to constrain the internal ice velocity and basal motion in the modern day. Both our modeling and field observations show that the surface velocity of the glacier has decreased over this period and reduced basal motion is mostly responsible for the observed slow-down. Lower basal velocities could result in a stabilizing feedback, which reduces the rate of ice mass loss in the coming decades. We then investigated the dynamics of the 2020-22 Henteel No’ Loo’ (Muldrow Glacier), Alaska, USA surge. My coauthors and I utilized satellite data, GPS stations, and a ground-based radar interferometer to observe the surface velocity before, during, and after, the surge. We find that the surge reached maximum velocities of 20-25 meters per day and find evidence suggesting this may be an upper velocity limit for the surge. This dissertation shows that basal motion is a primary control on glacier velocities for both surging and non-surging glaciers over multi-decadal to centennial timescales.