WATER STORAGE AND SUBGLACIAL DRAINAGE CONDITIONS INFERRED FROM BOREHOLE MEASUREMENTS ON GORNERGLETSCHER, VALAIS, SWITZERLAND

Measurements of change in length of a borehole, or displacements of po les and of subglacial water pressure were combined with drainage tests and electrode tests in boreholes. in experiments near the northern ma rgin of Gornergletscher, Valais, Switzerland, at the upstream side of an overdeepening. The measurements suggest that the subglacial drainag e system consisted of discrete conduits at that location, presumably l inked cavities on ''clean'' bedrock. Changes in subglacial water press ure were followed by variations in subglacial water storage, together with similar variations in elevation of a pole. The variations in subg lacial water storage caused changes in cross-sections of subglacial pa ssageways and thereby changed the frequencies of slug-test oscillation s. Similar experiments conducted near the center line of the glacier r evealed different subglacial conditions: impeded drainage through a se diment layer, and different depths of water levels in different boreho les. These results are discussed in relation to previous studies.