Challenges in predicting Greenland supraglacial lake drainages at the regional scale

Abstract

Abstract. A leading hypothesis for the mechanism of fast supraglacial lake drainages is that transient extensional stresses briefly allow crevassing in otherwise compressional ice flow regimes. Lake water can then hydrofracture a crevasse to the base of the ice sheet, and river inputs can maintain this connection as a moulin. If future ice sheet models are to accurately represent moulins, we must understand their formation processes, timescales, and locations. Here, we use remote-sensing velocity products to constrain the relationship between strain rates and lake drainages across ∼ 1600 km2 in Pâkitsoq, western Greenland, between 2002–2019. We find significantly more extensional background strain rates at moulins associated with fast-draining lakes than at slow-draining or non-draining lake moulins. We test whether moulins in more extensional background settings drain their lakes earlier, but we find insignificant correlation. To investigate the frequency at which strain-rate transients are associated with fast lake drainage, we examined Landsat-derived strain rates over 16 and 32 d periods at moulins associated with 240 fast-lake-drainage events over 18 years. A low signal-to-noise ratio, the presence of water, and the multi-week repeat cycle obscured any resolution of the hypothesized transient strain rates. Our results support the hypothesis that transient strain rates drive fast lake drainages. However, the current generation of ice sheet velocity products, even when stacked across hundreds of fast lake drainages, cannot resolve these transients. Thus, observational progress in understanding lake drainage initiation will rely on field-based tools such as GPS networks and photogrammetry.

Seasonal flow types of glaciers in Sermilik Fjord, Greenland, over 2016–2021

“…EOF/PC analysis forces random or otherwise non-coherent variability into higherorder modes. This variability can be due to random errors, grid artifacts, or other specific circumstances that interfere with image correlation, such as cloudiness or water at the surface (Poinar & Andrews, 2021). We found such features in modes 3 and higher (Midgard and Fenris Glaciers), mode 5 and higher (Helheim Glacier) or mode 8 and higher (Pourquoi Pas Glacier).…”

Observed and modeled moulin heads in the Pâkitsoq region of Greenland suggest subglacial channel network effects

“…When it was explored in 2018, Phobos had been active for at least two years; in each melt year, the stream feeding it flowed in from a slightly different direction, melting the walls from different sides, which, among other things, could have enlarged the near-surface chamber. Inventories of moulins in this same area suggest that reuse for 2-3 years is common among lake-draining moulins (Poinar and Andrews, 2021;Andrews, 2015), however, the stream typically flows in from a consistent direction. MouSh model runs over a single melt season (Andrews et al, 2022) are able to predict neither this size nor the overhung shape observed in Phobos Moulin.…”

Drill-site selection for cosmogenic-nuclide exposure dating of the bed of the Greenland Ice Sheet

“…In this way, one can address the criterion of being most likely to be safe for air support and/or access via traverse vehicles. We use a strain-rate field from Poinar and Andrews (2021) and a threshold value of 0.005 per year, above which crevasses are likely to form (Joughin et al, 2013). This analysis further reduces the area of the GrIS suitable for drilling from 6.8 % to 4.8 % (Fig.…”