Water flow through sediments and at the ice-sediment interface beneath Sermeq Kujalleq (Store Glacier), Greenland

• Main Authors: Doyle, S, Hubbard, B, Christoffersen, P, Law, R, Hewitt, D, Neufeld, J, Schoonman, C, Chudley, T, Bougamont, M
• Format: Article in Journal/Newspaper
• Language: English
• Published: International Glaciological Society 2021
• Subjects: Greenland; Kujalleq; glacier; greenlandic; Journal of Glaciology; Sermeq Kujalleq
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10139201/8/Hewitt_water-flow-through-sediments-and-at-the-ice-sediment-interface-beneath-sermeq-kujalleq-store-glacier-greenland.pdf; https://discovery.ucl.ac.uk/id/eprint/10139201/

Subglacial hydrology modulates basal motion but remains poorly constrained, particularly for soft-bedded Greenlandic outlet glaciers. Here, we report detailed measurements of the response of subglacial water pressure to the connection and drainage of adjacent water-filled boreholes drilled through kilometre-thick ice on Sermeq Kujalleq (Store Glacier). These measurements provide evidence for gap opening at the ice-sediment interface, Darcian flow through the sediment layer, and the forcing of water pressure in hydraulically-isolated cavities by stress transfer. We observed a small pressure drop followed by a large pressure rise in response to the connection of an adjacent borehole, consistent with the propagation of a flexural wave within the ice and underlying deformable sediment. We interpret the delayed pressure rise as evidence of no pre-existing conduit and the progressive decrease in hydraulic transmissivity as the closure of a narrow (< 1.5 mm) gap opened at the ice-sediment interface, and a reversion to Darcian flow through the sediment layer with a hydraulic conductivity of ≤ 10−6 m s−1. We suggest that gap opening at the ice-sediment interface deserves further attention as it will occur naturally in response to the rapid pressurisation of water at the bed.