RESPONDER boreholes shed new light on hydrological systems at the ice-bed interface

Subglacial hydrological systems lubricate the basal motion of glaciers. In Greenland, few observations exists and it is our core mission in RESPONDER to address this paucity of observations by drilling boreholes to the base of Store Glacier (Sermeq Kujalleq). In a new study, 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 beneath the glacier, and the forcing of water pressure in hydraulically-isolated cavities by elastic 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 gap or conduit and the progressive decrease in hydraulic transmissivity as the closure of a narrow (< 1.5 mm) gap which opened at the ice-sediment interface when our borehole connected with the sedimentary glacier bed. The findings 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 though other mechanisms, including lakes that drain and deep fractures that propagate all the way to the bed from the surface.

Doyle, S., Hubbard, B., Christoffersen, P., et al. (2021). Water flow through sediments and at the ice-sediment interface beneath Sermeq Kujalleq (Store Glacier), Greenland. Journal of Glaciology, 1-20. doi:10.1017/jog.2021.121