HR: 0830h
AN: C31B-0397    [PDF]
TI: Time-lapse monitoring of subglacial drainage conditions using borehole electrical surveying
AU: * Kulessa, B
EM: b.kulessa@qub.ac.uk
AF: Queen's University Belfast, School of Civil Engineering, Belfast, BT9 5AG United Kingdom
AU: Hubbard, B
EM: byh@aber.ac.uk
AF: University of Wales Aberystwyth, Institute of Geography and Earth Sciences, Aberystwyth, SY23 3DB United Kingdom
AU: Brown, G H
EM: g.h.brown@bris.ac.uk
AF: University of Bristol, School of Geographical Sciences, Bristol, BS8 1SS United Kingdom
AB: Subglacial electrical surveying has so far been poorly documented, although existing case studies at warm-based glaciers are encouraging. The particular advantage of such methods over other common techniques is their ability to produce multi-dimensional images especially of subglacial hydrological phenomena. This supports interpolation between measurements in single boreholes, which is otherwise often insufficient or error-prone in characterising such typically highly heterogeneous conditions. We present electrical resistivity data recorded at the base of four boreholes drilled through Haut Glacier d'Arolla, Valais, Switzerland. The resistivity data, acquired repetitively every hour over two diurnal hydrological cycles in the late melt season, were inverted in 3-D. The resulting repeat images reflect time-lapse resistivity changes in the subglacial sediment layer, and were correlated with water resistivity data recorded between the boreholes using a modified version of Archie's law. The correlation matrices reflect preferential subglacial water flow in the eastern part of the study area, and more distributed flow in the western part. Application of the modified law allows estimation of the true intrinsic formation factor by plotting the apparent formation factor (bulk sediment resistivity divided by water resistivity) against water resistivity. Use of Archie's law and the Kozeny-Carman equation then allows estimation of the porosity and hydraulic conductivity of the subglacial sediments, respectively. These results complement earlier findings from electrical self-potential modelling, which are briefly reviewed. We conclude that subglacial electrical surveying has the capacity to support interpolation of single-borehole hydrological data across the glacier bed.
DE: 0915 Downhole methods
DE: 0925 Magnetic and electrical methods
DE: 1827 Glaciology (1863)
DE: 1836 Hydrologic budget (1655)
DE: 5114 Permeability and porosity
SC: Cryosphere [C]
MN: 2003 Fall Meeting