Abstract
AbstractSurface crevasses on the Greenland Ice Sheet (GrIS) capture nearly half of the seasonal runoff, yet their role in transferring meltwater to the bed has received little attention relative to that of supraglacial lakes and moulins. Here, we present observations of crevasse ponding and investigate controls on their hydrological behavior at a fast‐moving, marine‐terminating sector of the GrIS. 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 to 2019 an average of 26% of the crevassed area exhibited ponding at locations that remained persistent between years despite rapid advection. We find that the spatial distribution of ponded crevasses does not relate to previously proposed controls on 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. This contrasts with unponded crevasse fields, which we suggest are readily able to transport meltwater 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 influences a spatially heterogeneous transfer of meltwater through crevasses to the bed of ice sheets, with consequences for processes, such as subglacial drainage and the heating of ice via latent heat release by refreezing meltwater.
Highlights
Surface crevasses are open fractures in glaciers and ice sheets ranging in width from millimeters to tens of meters and in length from tens of meters to kilometers
Crevasses are a visible expression of a glacier’s surface stress regimes; the size and orientation of crevasses are intrinsic to glacier dynamics as they are formed by extensional flow and deformation of ice through compression or shear (Colgan et al, 2016)
Our analysis of regional satellite data and local uncrewed aerial vehicle (UAV) surveys has demonstrated that crevasses instead exhibit spatially variable but inter-annually persistent hydrology across a ∼2,700 km2 marine-terminating sector of the western Greenland Ice Sheet (GrIS)
Summary
Surface crevasses are open fractures in glaciers and ice sheets ranging in width from millimeters to tens of meters and in length from tens of meters to kilometers. Studying crevasses provides insight into glacier flow (Dell et al, 2019; Phillips et al, 2013) and it is important for the development of fracturing criteria for supraglacial lake drainage Supraglacial lakes deliver less total meltwater volume to the ice sheet bed than do crevasse fields, which may capture as much as half of seasonal surface runoff (Koziol et al, 2017; McGrath et al, 2011). Other studies suggest crevasse fields continuously, but inefficiently, transmit a low water flux to the subglacial system without the need for fulldepth hydrofracture (Colgan et al, 2011; McGrath et al, 2011). No studies account for the full spectrum of observations and assumptions surrounding the routing of water through crevasse fields
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