Abstract
Supraglacial lake drainage events are common on the Greenland Ice Sheet. Observations on the west coast typically show an up-glacier progression of drainage as the annual melt extent spreads inland. We use a suite of remote sensing and modelling techniques in order to study a series of lakes and water-filled crevasses within 20km of the terminus of Helheim Glacier, south east Greenland. Automatic classification of surface water areas shows a down-glacier progression of drainage, which occurs in the majority of years between 2007 and 2014. We demonstrate that a linear elastic fracture mechanics model can reliably predict the drainage of the uppermost supraglacial lake in the system, but cannot explain the pattern of filling and draining observed in areas of surface water downstream. We propose that the water levels in crevasses downstream of the supraglacial lake can be explained by a transient high-pressure wave passing through the subglacial system following the lake drainage. We support this hypothesis with analysis of the subglacial hydrological conditions, which can explain both the position and interannual variation in filling order of these crevasses. Similar behaviour has been observed in association with jokulhaups, surging glaciers, and Antarctic subglacial lakes, but has not previously been observed on major outlets of the Greenland Ice Sheet. Our results suggest that the behaviour of near-terminus surface water may differ considerably from that of inland supraglacial lakes, with the potential for basal water pressures to influence the presence of surface water in crevasses close to the terminus of tidewater glaciers.
Highlights
A summary of results from all years is shown in Figure 3, full results from the automatic classification of surface water for all years are included in the supplementary material (Figures S3 - S10)
We have observed an unusual pattern of growth and drainage of a lake and water-filled crevasses near the terminus of Helheim Glacier, south east Greenland, which is consistent over an eight year period
A combination of remote sensing observations and modelling have been used to demonstrate that hydrofracture is unlikely to explain the observed behaviour
Summary
Bartholomew et al, 2010] time-scales These increases in flow speed may be driven by high water pressures in the subglacial system, which reduce basal friction and lead to rapid sliding [Iken, 1981; Iken and Bindschadler , 1986; Meier et al, 1994]. This mechanism has been observed at Helheim Glacier, where ice velocity lags surface meltwater production by one day [Andersen et al, 2011], as well as at tidewater glaciers on the west coast of Greenland [Sole et al, 2011], and in Alaska [Kamb et al, 1994; Oneel et al, 2001].
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