Stress coupling between neighboring supraglacial lakes during rapid drainage

Abstract:

Remote sensing studies report clusters of supraglacial lakes on the Greenland Ice Sheet draining close together in space and time, leading to the hypothesis that transmission of stresses between lake basins may allow the rapid drainage of one lake to trigger others to drain. However, strain rates calculated from the highest temporal-resolution remotely sensed surface-velocity data (e.g., Landsat GoLive) cannot resolve the short-lived (<1 day duration) changes in strain rate involved in the triggering of lake-draining hydro-fractures. Here we investigate stress transmission across three adjacent Greenland supraglacial lake basins in the mid-ablation zone (1000-m ice thickness) in 2011 and 2012. Using Global Positioning System (GPS) observations of ice-sheet surface displacement, we investigate surface strain rates across the basins and use a Network Inversion Filter to estimate basal slip and uplift at the ice-bed interface to forward model surface stresses. In both years, the rapid drainage of a central lake results in concurrent, positive (extensional) surface strain rates and stresses across a lake basin 2.5 km to the south, but negative (compressional) strain rates and stresses across a lake basin 3.5 km to the north. Strain rates across all three lake basins return to background values within 12 hours of the central lake’s drainage initiation. Compressional stresses tend to inhibit crevasse formation that could lead to hydro-fracture and rapid drainage. Thus, in this set of lakes, a rapid lake drainage of one lake does not always promote drainage in a neighboring basin, but in some cases makes stress conditions less favorable for initiating hydro-fracture. We observe transient lake drainage stresses to be low in magnitude (±50 kPa) over 6 km away from the draining lake. This fall-off in transient stress magnitude suggests that the stress-coupling length scale for a single lake drainage in this region is less than 10 km. Additional field observations are required to quantify stress-coupling length scales in the mid- to upper-ablation zone. As the extent of supraglacial lakes advances inland, quantifying stresses in nascent supraglacial lake basins is necessary to determine if these lakes will create localized pathways for meltwater to access the bed and, if so, modulate ice flow in the interior.