DIURNAL FLUCTUATIONS IN SURFACE WATER INPUT, SUBGLACIAL WATER PRESSURE, STREAM DISCHARGE, AND GLACIER SURFACE VELOCITY, BENCH GLACIER, ALASKA

Observations of melt water input, subglacial water pressure, stream discharge, and surface velocity along the length of Bench Glacier, Alaska all show a season of distinct diurnal fluctuations. Measurements of subglacial water pressure were taken during three melt seasons at 43 different boreholes spanning the entire length of the glacier. Over the final two seasons, surface velocities were recorded with differential GPS at four locations and a surface energy balance model was constructed to determine the hourly melt water input. Glacier surface velocities were typically low, roughly 0.03m/day, though often ranged daily between 0.05m/day and 0.01m/day. Diurnal water pressure fluctuations were commonly large, up to 80% of overburden pressure. Preliminary analysis suggests that diurnal fluctuations in surface velocity and subglacial water pressure did not have a simple correlation. The timing of the daily peak subglacial water pressure steadily migrated earlier in the day throughout the first half of the melt season, from around mid-night (0:00-2:00AM) to late afternoon (16:00-18:00PM). The timing of peak water pressure also tended to occur slightly earlier in the day at boreholes located lower on the glacier. A comparison of the peak times in water pressure, stream discharge and surface water input can be used to help determine the transmissivity of the glacier drainage system and the dominant drainage pathways.