Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages

Abstract

Surface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we infer drainage system transmissivity based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity (from 0.8 ± 0.3 $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 to 215 ± 90.2 $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 ) as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes driven by seasonal meltwater input.

Growth of a fluid-infused patch from droplet drainage into a thin porous layer

“…2021; Lai et al. 2021). These observations are more consistent with the assumption of a pinned contact line during the drainage process, as made in Case (ii) of the droplet drainage model.…”

“…It is also of interest to note that in the analogue problem of fluid drainage from beneath an elastic sheet, it is also observed that the location of the contact line remains approximately pinned, as the fluid gradually drains into the thin porous layer underneath (Chase, Lai & Stone 2021; Lai et al. 2021).…”

“…Lai et al. 2016, 2021; Chase et al. 2021), where simple models were derived based on experimentally observable evolution of the contact-line location and without fitting parameters.…”

“…O(10 −2 ) s. While the time evolution of the apparent contact angle was not reported in this study for us to impose a comparison between the theoretical prediction and experimental measurements, these experiments demonstrate that the regime of Case (ii) of the current model indeed exists. It is also of interest to note that in the analogue problem of fluid drainage from beneath an elastic sheet, it is also observed that the location of the contact line remains approximately pinned, as the fluid gradually drains into the thin porous layer underneath Lai et al 2021).…”

Controls on Greenland moulin geometry and evolution from the Moulin Shape model

“…On length scales considerably larger than ∼ 1 m moulins, as well as in problems where elastic flexure is more central to the geometry, elastic deformation remains important. These applications include ice shelves (e.g., Reeh et al, 2003;, large marine-terminating glaciers (Christmann et al, 2021), crevasse opening (Poinar et al, 2017), and rapid supra-and subglacial lake drainage (Dow et al, 2016(Dow et al, , 2015Lai et al, 2021).…”