Multi-annual patterns of rapidly draining supraglacial lakes in Northeast Greenland

Abstract. Supraglacial lakes are known to undergo rapid drainages in which their water masses are drained through ice hydrofracture to the glacier bed, typically within several hours. Despite the impact of this sudden englacial transport of meltwater, the conditions leading up to a rapid drainage are not fully understood. In this study, the spatial and temporal variability of rapid drainages was evaluated over two major glaciers in Northeast Greenland: Zachariæ Isstrøm and Nioghalvfjerdsfjorden (79N Glacier). Over the 2016–2022 summer melt seasons, supraglacial lakes on these glaciers were tracked via Sentinel-2 optical imagery to find the occurrence of any rapid drainages. The spatial distribution of rapid drainages as well as the seasonal timings was then evaluated against several other factors, such as ice strain rate, elevation, lake volume, and seasonal surface temperature. It was found that the drainage patterns of individual lakes varied substantially, with some lakes having drained only a couple times and others nearly every year in the observed time frame. Furthermore, the temporal consistency and spatial consistency of drainages were also generally inconsistent. Some lakes tended to drain at similar times over the melt years, while others had a more sporadic drainage timing. Similarly, certain clusters of lakes tend to drain in similar time frames, whereas it was found that most lakes did not follow a drainage tendency based on spatial position. However, the phenomenon of cascading drainages, in which neighboring lakes drain nearly simultaneously, was observed several times. While it was seen that drainages tend to occur later with higher elevations, little correlation was found between the occurrence of rapid drainages and the other investigated factors. It appears several conditions would need to be met to allow for a rapid drainage to occur, particularly the existence of fractures or crevasses within the lake boundaries.