Evolution of Seasonal Variations in Motion of the Kaskawulsh Glacier, Yukon Territory

Abstract

Differential GPS data from 2007-2014 are used to assess horizontal and vertical velocity variations of the Kaskawulsh Glacier at interannual and intra-annual timescales. These indicate that an upglacier propagating high velocity event occurs every spring at the onset of melt, and that a downglacier propagating high velocity event occurs every fall or winter after melt has finished. These events suggest that the subglacial drainage system alternates between a distributed system in the winter and channelized system in the summer and fall. In addition, there is a strong negative correlation between summer melt and velocity the following fall and winter, with strong melt years resulting in low velocities. For each additional metre of summer melt, an 8.6% average decrease in velocity is observed on the glacier the following fall-winter. These results suggest that changes in the subglacial drainage system limit the sensitivity of glacier motion to increased meltwater inputs. Glacier motion will likely show a net decrease under a warming climate due to the negative correlation between surface melt rates and ice motion and a decrease in driving stresses as a result of reduced ice thicknesses. In addition, future fall-winter velocity patterns could be accurately predicted from only a month or two of summer melt data, with May-June melt providing the best indication of fall-winter motion. This study also suggests that the common assumption that glaciers are ‘stable’ in the late fall and winter is incorrect.