Ice dynamic and hydrological response to ice-dammed lake drainages at Isunnguata Sermia, West Greenland

Ice-marginal lakes are increasingly common around Greenland and are important for modulating glacier runoff and dynamics. This study investigates the evolution of a ~3 km² and up to ~100 m deep ice-dammed lake at Isunnguata Sermia, West Greenland. Satellite observations between 1987 and 2024, and field observations of a 2023 drainage using passive seismics, GNSS and time-lapse imagery reveal that the lake drains subglacially and has undergone 12 fill-drain cycles since 1987, a drainage periodicity of 1-3 years. Peak lake volume has decreased since 2010, associated with glacier thinning. Lake drainage can perturb the wider subglacial hydrology system, including triggering the release of stored subglacial water along the flood path in 2019. During the extreme melt year of 2012, the lake drained but did not refill, suggesting that subglacial leakage under the ice dam was sustained by record runoff. Transient ice flow acceleration was observed during the late season drainage in 2023 when the subglacial hydrological system was less efficient and therefore more easily pressurised. Our results indicate that ice-dammed lake fill-drain cycles, and the downstream impact on subglacial hydrology and ice dynamics, are modulated by ice dam thickness, melt supply and the antecedent subglacial hydraulic capacity.