EEPS Colloquium: Grace Barcheck

Response of the basal hydrologic network to spring melt onset, Greenland Ice Sheet

How the Greenland Ice Sheet ablation zone responds to basal meltwater input depends partly on the shape and evolution of the subglacial drainage network, which is difficult to observe. This network is thought to be a patchwork of water-filled cavities, saturated till, and efficient conduits, with variable connectivity among patches and to moulins, and with variable effects on basal friction. To document the structure of this connectivity in West Greenland during the onset of melt in 2018, we recorded changes in dozens of families of high frequency repeating basal icequakes, which have stick-slip, basal crevassing, or ambiguous mechanisms. Repeating basal stick-slip and crevassing events can respond to changes in basal hydrology, and we evaluate each family for continuity across melt onset. We interpret repeaters that don’t change in response to melt onset as indicating  bed regions that are hydraulically isolated from moulins, while events that disappear or change indicate more-connected bed regions. Geodetic data show limited local sliding acceleration until several weeks later, implying that basal seismicity changes result primarily from changes in basal hydrology, not sliding. Repeaters affected and unaffected by melt onset are interspersed at sub-km scales, indicating that connected versus isolated regions of the hydrologic network are likewise interspersed. Interestingly, basal seismicity patterns appear unrelated to formation of a subglacial channel also recorded by the network. These results suggest that subglacial hydraulic connectedness can vary over short distances, and that seismic observations of icequakes are a useful way to observe hydrologic evolution.

Host: Dougal Hansen

 EEPS Colloquia are made possible by the William C. Ferguson Fund