How far away can a rapidly draining supraglacial lake induce a crevasse?
Abstract
When a crevasse opens beneath a supraglacial lake, water can hydrofracture through the ice to the glacier bed, rapidly draining the lake and creating a moulin. The drained lake water moves along the contact between the glacier and its bed, altering the local basal slipperiness as it goes. This temporarily changes the velocity and strain rate fields at the ice sheet surface, which has been hypothesized to lead to the formation of new crevasses and possibly a chain reaction of lake drainages. Currently, lake-drainage-induced changes in basal slipperiness and how far from the draining lake these strain-rate perturbations may produce new crevasses are both underconstrained. To better constrain these factors, we investigate rapid lake drainage events recorded during the summer of 2011 by 11 global positioning system (GPS) stations along the flow path of the Sermeq Avannarleg catchment in the Paakitsoq region of western Greenland. We difference velocities recorded at the GPS stations to generate strain rates at 22 points with a spatial resolution of 4 km or more. However, crevasses may open in response to higher-magnitude, hyperlocal strain rates that are not captured by the GPS data. To increase spatial resolution to 150 m, we apply an analytical ice-flow model (Gudmundsson, 2003) to calculate surface strain rates induced by hypothetical basal slipperiness perturbations. We calibrate the basal slipperiness parameter in this model using the GPS data, local surface and bed digital elevation models, and surface ice-flow fields. We then systematically place basal slipperiness perturbations of varying dimensions and sliding coefficients into the model beneath the observed lake drainage locations and advect them along likely subglacial hydrologic pathways. This allows us to determine how far from the initial lake drainage, and in which directions, crevassing may occur over the ice sheet surface. This research is a step toward understanding how the Greenland Ice Sheet may respond to future warming, increased surface melt volumes, and the anticipated inland migration of supraglacial lakes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.C13C1314S
- Keywords:
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- 0720 Glaciers;
- CRYOSPHERE;
- 0726 Ice sheets;
- CRYOSPHERE;
- 0730 Ice streams;
- CRYOSPHERE;
- 0776 Glaciology;
- CRYOSPHERE