Thursday, 12 November 2009
Glaciers along the Gulf of Alaska are thinning and retreating rapidly and over the last century this loss of ice has contributed measurably to global sea level rise. An important control on the rate at which ice is being lost is basal motion because higher glacier velocities increase the rate at which ice is delivered to ablation zones. Recent research has focused on understanding the effects of a sub-glacial water storage system in conjunction with glacier basal motion. In this study, we examined how water inputs from large rainfall events as well as a glacier lake outburst flood affected the velocity of the Lemon Creek Glacier in southeastern Alaska. Lemon Creek Glacier is a moderately sized (14 km2) temperate glacier at the margin of the Juneau Icefield. An ice- marginal lake forms at the head of the glacier and catastrophically drains at least once every melt season. We have instrumented the glacier with two meteorological stations: one at the head of the glacier near the ice-marginal lake and another several kilometers below the terminus. These stations measure temperature, relative humidity, precipitation, incoming solar radiation, wind speed and direction. Lake stage in the supraglacial lake was monitored with a pressure transducer. In addition, Lemon Creek was instrumented with a water quality sonde at the location of a USGS gauging station approximately 3 km downstream from the glacier terminus. The sonde provides continuous measurements of water temperature, dissolved oxygen, turbidity and conductivity. Finally, three Trimble NetRS dual frequency, differential GPS units were deployed on the glacier center line at top, mid, and bottom portions of the glacier. All of the instruments were run continuously therefore we captured the outburst flood associated with the ice-marginal lake drainage as well as several large (>3~cm) rainfall events associated with frontal storms off of the Gulf of Alaska in late summer. With this combined data it allows us to test the hypothesis that water inputs which overwhelm subglacial drainage networks result in increased velocity rates of basal motion.
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