Seasonal Variability of Ice Motion for Hubbard and Valerie Glaciers, Alaska

Abstract

Hubbard Glacier is a large, fast-flowing, tidewater-terminating glacier in the Saint Elias Mountains. It is connected at its terminus to Valerie Glacier. Although Hubbard Glacier has been shown to experience large intra-annual velocity changes and a long-term deceleration, previous seasonality studies have had limited timescales without a dense record of motion. Valerie Glacier’s variability has also been understudied, with only one study reporting its seasonal behaviour. The goal of the current study was to combine ITS_LIVE, RADARSAT-2, RADARSAT Constellation Mission, and TerraSAR-X/TanDEM-X – derived velocity data to create the densest record of motion ever constructed for Hubbard and Valerie glaciers for a period from July 2013 to April 2022, in order to explore seasonal velocity variability of both glaciers. We used air temperature (NCEP-NCAR Reanalysis) to estimate surface melt on the glaciers, which we explored as a potential driver for seasonal velocity changes. Valerie Glacier had a seasonal pattern of fast flow in May, with minimum flow between August and November before accelerating again. We found a unique seasonal pattern that has not been previously observed on Hubbard Glacier, with two periods of fast motion: one in May and one in December – February. Considering our findings and insights from other recent research, we inferred that the spring peaks and late summer/fall minimums on both glaciers are due to meltwater reaching the glacier bed and influencing the subglacial hydrology. We did not determine the cause of the winter peak and slight velocity drop before the spring peak on Hubbard Glacier, suggesting this should be a topic for future studies, although we hypothesize that the glacier’s geometry influences these changes.