GEOMETRY, BED TOPOGRAPHY AND DRAINAGE SYSTEM STRUCTURE OF THE HAUT GLACIER DAROLLA, SWITZERLAND

As part of an integrated study of the hydrology, meltwater quality and dynamics of the Haut Glacier d'Arolla, Switzerland, the glacier's dra inage network structure was determined from patterns of dye recovery i n 342 injection experiments conducted from 47 moulins distributed wide ly across the glacier. This structure was compared with theoretical pr edictions based upon reconstructed patterns of water flow governed by (a) the subglacial hydraulic potential surface, and (b) the subglacial bedrock surface. These reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio-echo sounding techniques. The two reconstructions si mulate the drainage system structures expected for (a) closed channels , in which water is pressurized by the overlying ice, and (b) gravity- driven, open-channel flow. The closed-channel model provides the best fit to the observed structure, even though theoretical calculations su ggest that, under summer discharge conditions, open-channel flow may b e widespread beneath the glacier. Possible reasons for this apparent d iscrepancy are discussed.