Modelling the effects of proglacial lake filling and drainage on lake-terminating glacier dynamics

Abstract. The rapid retreat of glaciers worldwide is leading to the formation and expansion of proglacial and ice-marginal lakes. Proglacial lakes not only influence glacier dynamics and contribute to accelerated mass loss, but also pose a growing risk of Glacial Lake Outburst Floods (GLOFs), particularly as warming intensifies in polar and high-mountain regions. Despite important feedbacks between glacier behaviour and lake expansion, ice–lake interactions remain understudied compared to ice–ocean processes, introducing considerable uncertainty in projections of future mass loss. In this study, we use the Ice-sheet and Sea-level System Model (ISSM) in a semi-synthetic domain to explore a critical, yet often overlooked, aspect of ice–lake interaction: lake level fluctuations driven by filling and drainage events. We find that lake-terminating glaciers experience thinning and enhanced velocities compared to glaciers with a land terminus, consistent with widely observed responses to proglacial lake damming; these responses manifest even at low water levels but increase with lake depth. The lake influence extends beyond the immediate basin, as ice thickness and velocity changes propagate upstream and to neighbouring outlets. Our results also reveal that glacier responses to lake level fluctuations are highly non-linear. The onset of flotation due to rising lake levels dramatically increases grounding line mass flux and, depending on relative magnitudes of lake filling and glacier thinning, may lead to rapid retreat. Steady lake drainage instead reduces mass loss. However, we find that rapid drainage events (seasons to years) can destabilise the ice front by altering the stress regime sufficiently to enhance crevasse formation and calving. Our findings imply that while sudden drainage events may exacerbate lake-triggered glacier instability, controlled, gradual lake drainage may serve as a viable geoengineering approach to mitigate glacier mass loss and related flood hazards.