Abstract
Surface crevasses on the Greenland Ice Sheet capture nearly half of the
seasonal runoff, yet their role in transferring meltwater to the bed has
received little attention compared to that of supraglacial lakes and
moulins. Here, we present observations of crevasse ponding and
investigate controls on their hydrological behaviour at a fast-moving,
marine-terminating sector of the Greenland Ice Sheet. We map surface
meltwater, crevasses, and surface-parallel stress across a
~2,700 km² region using satellite data and
contemporaneous uncrewed aerial vehicle (UAV) surveys. From 2017-2019 an
average of 26% of the crevassed area exhibited ponding at locations
that remained persistent between years despite rapid advection rates. We
find that the spatial distribution of ponded crevasses does not relate
to previously proposed methods for predicting the distribution of
supraglacial lakes (elevation and topography) or crevasses (von Mises
stress thresholds), suggesting the operation of some other physical
control(s). Ponded crevasse fields were preferentially located in
regions of compressive surface-parallel mean stress, which we interpret
to result from the hydraulic isolation of these systems, in contrast to
unponded crevasse fields, which we suggest are able to drain into the
wider supraglacial and englacial network. UAV observations show that
ponded crevasses can drain episodically and rapidly, likely through
hydrofracture. We therefore propose that the surface stress regime
informs a spatially heterogeneous transfer of meltwater through
crevasses to the bed of ice sheets, with potential consequences for
processes such as subglacial drainage and the heating of ice via latent
heat release by refreezing meltwater.