A FIELD EXPERIMENT TO EXPLORE DRAINAGE PROCESSES THROUGH SUBGLACIAL SEDIMENTS AND THEIR INFLUENCE ON SEDIMENT DEFORMATION

The upper part of a sedimentary sequence consisting of till overlying a thick sand and gravel aquifer was instrumented with water pressure transducers before an impending advance of the glacier Breidamerkurjökull overrode the site. Transducers continued to function for up to 180 days after glacier advance over the site, and water pressures increased as the advance proceeded. Water pressures fluctuated diurnally, very strongly within the till and less strongly within the underlying aquifer, because of the high transmissibility of the latter. Water movement was predominantly down through the till, but in areas where the ice base was unfractured, upward movement occurred during diurnal period of high melt rate.

Relationships are inferred between the patterns of water pressure change and patterns of deformation within the till, and the extent to which sustained undrained loading can occur. The three dimensional distribution of hydrogeological properties may account for the patterns of till deformation and distribution. The geotechnical behaviour of the subglacial sediment mass, and its role in influencing basal movement were fundamentally influenced by groundwater flow.