Erik Matthew Young, Gwenn Elizabeth Flowers, Etienne Berthier, Rebecca Latto

The Kaskawulsh Glacier is an iconic outlet draining the icefields of the St. Elias Mountains in Yukon, Canada. We determine and attempt to interpret its catchment-wide mass budget since 2007. Using SPOT5/6/7 data we estimate a 2007-2018 geodetic balance of $-$0.46 $\pm$ 0.17 m w.e. a$^{-1}$. By comparing computed balance fluxes with observed ice fluxes at nine flux gates we examine the discrepancy between the climatic mass balance and internal mass redistribution by glacier flow. Balance fluxes are computed using a fully distributed mass-balance model driven by downscaled and bias-corrected climate-reanalysis data. Observed fluxes are calculated using NASA ITS_LIVE surface velocities and glacier cross-sectional areas derived from ice-penetrating radar data. We find the glacier is still in the early stages of dynamic adjustment to its mass imbalance. We estimate a committed terminus retreat of $\sim$23 km under the 2007-2018 climate and a lower bound of 46 km$^3$ of committed ice loss, equivalent to $\sim$15\% of the total glacier volume. By combining our observations and model output using the continuity equation, we highlight challenges and opportunities in exploring the mass budget of large land-terminating glaciers.