Investigations of Glacier Hydrological Systems using Dye Tracer Techniques: Observations at Pasterzengletscher, Austria

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Abstract
A comprehensive series of dye tracer tests was undertaken over two summers at Pasterzengletscher, Austria, and from these a number of important conclusions can be drawn. A lateral division of drainage on the lower tongue was proved, but this was not determined by the direction of oblique crevasses. Water from many moulins passed into two or more drainage courses, as shown by repeated patterns of multiple peaks on the time/concentration curves. The spatial pattern of travel times from different moulins on the tongue was complex, although it remained stable over time. Repeated tracer tests showed that throughflow velocities varied by up to an order of magnitude during a single day. Maximum velocities occurred at the time of peak discharge, and probably the large diurnal velocity variations are caused by changes in the proportion of the length which has channel-full pressure flow. However, seasonal velocity variations were much smaller, although changes in outflow discharge were larger than in the diurnal case. This gives strong support to the concept that channels adjust in size to the average water discharge passing through, and that these changes occur over a matter of days or a few weeks.