Borehole water-level variation and the structure of the subglacial hydrological system of Haut Glacier d'Arolla, Valais, Switzerland

Late-summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of Haut Glacier d'Arolla. Interpolated surfaces of minimum diurnal water pressure and diurnal water-pressure variation suggest the presence of a subglacial channel within a more widespread distributed drainage system. Water-pressure variations recorded in boreholes reflect the delivery of surface-derived meltwater to the glacier bed and result in a diurnally reversing, transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight. Fine material is flushed from basal sediments located adjacent to large, melt-season drainage channels beneath warm-based glaciers. This process may have important implications for patterns of glacier erosion, hydrochemistry and dynamics. -from Authors