Wintertime Supraglacial Lake Drainage Cascade Triggers Large‐Scale Ice Flow Response in Greenland

Surface melt forces summertime ice‐flow accelerations on glaciers and ice sheets. Here, we show that large meltwater‐forced accelerations also occur during wintertime in Greenland. We document supraglacial lakes (SGLs) draining in cascades at unusually high elevation, causing an expansive flow acceleration over a ∼5,200 km2region during winter. The three‐component interferometric surface velocity field and decomposition modeling reveal the underlying flood propagation with unprecedented detail as it traveled over 160 km from the drainage site to the margin, providing novel constraints on subglacial water pathways, drainage morphology, and links with basal sliding. The triggering SGLs continuously grew over 40 years and suddenly released decades of stored meltwater, demonstrating surface melting can impact dynamics well beyond melt production. We show these events are likely common and thus their cumulative impact on dynamics should be further evaluated. Understanding factors that influence flow speeds on ice sheets are linked to our ability to predict changes in sea level and prepare coastal communities for the future. On the Greenland Ice Sheet, ice flow‐speed changes have long been linked to surface melting in summer. Meltwater can make it to the bed of the ice sheet via surface cracks causing changes in ice motion. Here, we show that melt that is produced during summer, but stored within lakes on the ice surface, can drain to the bed and cause large flow accelerations during winter. This demonstrates the influence of meltwater on flow speeds needs to be considered beyond when it is produced. A cascade of supraglacial lake drainages and an associated ice‐flow acceleration are observed during winter in GreenlandDecomposition of motion into vertical and horizontal components allows for subglacial water pathways and links with sliding to be inferredTracking the history of the supraglacial lakes shows some of the meltwater released was produced decades earlier A cascade of supraglacial lake drainages and an associated ice‐flow acceleration are observed during winter in Greenland Decomposition of motion into vertical and horizontal components allows for subglacial water pathways and links with sliding to be inferred Tracking the history of the supraglacial lakes shows some of the meltwater released was produced decades earlier