Subglacial hydrology can exert an important control on ice flow by affecting drag at the ice-bedrock interface. Here, we report on a series of subglacial drainage events (outbursts) along the Northeast Greenland Ice Stream (NEGIS), initiating as far inland as ~500 km from the margin of Zachariae Isstrøm. The drainage events are associated with local transient uplift, followed by prolonged subsidence, measured by satellite synthetic aperture radar interferometry (DInSAR). In downstream regions, drainage events are associated with a local speed-up in ice flow. The high spatiotemporal resolution of the DInSAR measurements allows for a detailed mapping of the drainage propagation pathway. We show that multiple drainage cascades have occurred along the same identified pathway over the years 2020-2022. Finally, the propagation speed of subglacial water flow is found to vary greatly along NEGIS, suggesting that fundamental differences may exist in the subglacial environment.
Surface melt forces summertime ice-flow accelerations on glaciers and ice sheets. Here, we show that large meltwater-forced accelerations also occur in winter in Greenland. We document supraglacial lakes (SGLs) draining in cascades at unusually high elevation, causing an expansive flow acceleration over a ~5200 km2 region during winter. The 3-component interferometric surface velocity field and decomposition modeling reveals 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 into regions of the bed never previously forced, demonstrating surface melt can impact dynamics well beyond its production. We show these events are common and thus their cumulative impact on dynamics should be further evaluated.