Preliminary results from hot-water drilling and borehole instrumentation on Store Glacier, West Greenland

Abstract:

As part of the Subglacial Access and Fast Ice Research Experiment (SAFIRE) pressurised hot water was used to drill four 603-616 m-long boreholes to the bed of the Greenland Ice Sheet at a site located 30 km from the calving front of fast-flowing, marine-terminating Store Glacier (70° N, ~1000 m elevation). Despite the boreholes freezing within hours, 4 wired sensor strings were successfully deployed in three of the boreholes. These included a thermistor string to obtain the englacial temperature profile installed in the same borehole as a string of tilt sensors to measure borehole deformation, and two sets of water pressure, electrical conductivity and turbidity sensors installed just above the bed in separate, adjacent boreholes. The boreholes made a strong hydrological connection to the bed during drilling, draining rapidly to ~80 m below the ice surface. The connection of subsequent boreholes was observed as a perturbation in water pressure and temperature recorded in neighbouring boreholes, indicating an effective hydrological sub- or en-glacial connection between them. The sensors, which were all connected to loggers at the surface by cables, operated for between ~30 and 80+ days before indications suggest that the cables stretched and then snapped – with the lowermost sensors failing first. The records obtained from these sensors reveal (i) high and increasing water pressure varying diurnally close to overburden albeit of a small magnitude (~ 0.3 m H₂O), (ii) a minimum extrapolated englacial temperature of -21°C with above-freezing temperatures at the bed, and (iv) high rates of internal deformation and strain increasing towards the bed as evinced by increasing tilt with depth. These borehole observations are complemented by GPS measurements of ice motion, meteorological data, and seismic and radar surveys.