Borehole drainage and its implications for the investigation of glacier hydrology: experiences from Haut Glacier d'Arolla, Switzerland

Studies of glacier hydrology rely increasingly on measurements made in bore holes as a basis for reconstructing the character and behaviour of subglaci al drainage systems. In temperate glaciers, in which boreholes remain open to the atmosphere following drilling, the interpretation of such data map b e complicated by supraglacial or englacial water flows to and from borehole s. We report on a suite of techniques used to identify borehole water sources and to reconstruct patterns of water circulation within boreholes at Haut G lacier d'Arolla, Switzerland. Results are used to define a number of boreho le 'drainage' types. Examples of each drainage type are presented, along wi th the manner in which they influence interpretations of borehole water-lev els, borehole water-quality data, and borehole dye Lr aces. The analysis in dicates that a full understanding of possible borehole drainage modes is re quired for the correct interpretation of many borehole observations, and th at those observations provide an accurate indication of subglacial conditio ns only under relatively restricted circumstances. Copyright (C) 2001 John Wiley & Sons, Ltd.