Characterizing supraglacial lake drainage and freezing on the Greenland Ice Sheet

Abstract. The behaviour of supraglacial lakes on the Greenland Ice Sheet has attracted a great deal of focus, specifically with regard to their fast drainage through hydrofracturing to the ice sheet base. However, a previous study has shown that this mode of drainage accounts for only 13% of the lakes on the Greenland Ice Sheet. No published work to date has studied what happens to those lakes that do not drain suddenly. We present here three possible modes by which lakes can disappear from the ice sheet, which will have strongly contrasting effects on glacial dynamics and the ice sheet water budget. Around half of all supraglacial lakes observed persisted through the melt season and froze at the end of summer. A third drained slowly, which we interpret to be a result of incision of the supraglacial lake exit-channel. The fate of 7% of lakes could not be observed due to cloud cover, and the remainder drained suddenly. Both fast and slow lake drainage types are absent at higher elevations where lakes tend to freeze despite having similar or longer life spans to lakes at lower elevations, suggesting the mechanisms of drainage are inhibited. Groups of neighbouring lakes were observed to drain suddenly on the same day suggesting a common trigger mechanism for drainage initiation. We find that great care must be taken when interpreting remotely sensed observations of lake drainage, as fast and slow lake drainage can easily be confused if the temporal resolution used is too coarse.