Reconstructing the Surge History and Dynamics of Fisher Glacier, Yukon, 1948-2022
Glacier surges are periods of dynamic instabilities which result in semi-regular alternating periods of slow flow, termed the quiescent phase, and fast flow, termed the active phase. This study uses remotely sensed imagery, digital elevation models, glacier velocity datasets, and in situ oblique photographs to reconstruct the surge history and dynamics of Fisher Glacier to better characterize surging in the southwest Yukon and assess the risk posed by this glacier’s surges on surrounding regions. Fisher Glacier has previously been identified as a surge-type glacier but, until now, it had not been the focus of any detailed studies. We find evidence that Fisher Glacier underwent two surges during the study period from 1948 to 2022. Visual analysis of characteristic surge features on the glacier surface show that the glacier was in quiescence from <1948 to at least 1963. In 1972, an advanced terminus position, intense surface crevassing, and high point velocities suggest that a surge had recently terminated, corroborating a previous report of a surge occurring around 1970. This was followed by a 40-year quiescent phase from ~1973-2013 during which the terminus underwent consistent retreat, totaling a terminus-wide average of 2058 ± 8 m (up to 3567 ± 8 m in certain sections). Velocities during the quiescent phase were low (generally <50 m yr⁻¹), but underwent a slow multidecadal increase starting around 1985, spreading from the center of the glacier towards the head and the terminus. A pre-surge buildup phase beginning in ~2008-2010 resulted in velocities of up to ~200 m yr⁻¹. The active phase of the surge initiated in winter 2013/14 and was characterised by a velocity increase to ~1500 m yr⁻¹ that propagated both up- and down-glacier from the surge nucleus in the mid-region (~22 km upglacier from the terminus). Velocities peaked at >2100 m yr⁻¹ in the winter/early spring of 2016 at ~12 km from the terminus. The surge resulted in a mean terminus-wide advance of 868 ± 8 m, intense surface crevassing and a downglacier transfer of mass from the reservoir zone to the receiving zone. The terminus area increased in elevation by a mean of ~80 m. In July 2016, the surge rapidly terminated within a period of ~1 month, although velocities at the head and the terminus took a few more months to slow to quiescent values. Since then, average annual velocities along the centerline have been lower than pre-surge velocities, the crevasses have closed up, and the rate of ice surface elevation change has been negative across the entire glacier. Fisher Glacier’s surge dynamics suggest predominantly hydrologically controlled surging, but with some aspects more representative of thermally controlled surging. Thus, we propose that more than one mechanism might be at play in controlling its surges, although further research is required to confirm this. Under current climate conditions, it is unlikely that Fisher Glacier could dam the nearby Alsek River and cause a glacier lake outburst flood.
Glaciology, Glacier Surging, Yukon, Fisher Glacier
Networked Digital Library of Theses and Dissertations
Université d'Ottawa / University of Ottawa