FLUVIAL GEOMORPHOLOGY OF SUPRAGLACIAL STREAMS ON THE MATANUSKA GLACIER, ALASKA

This study quantifies the migration of two supraglacial meandering streams on the Matanuska Glacier, south-central Alaska. Data was collected during the months of July and August: specifically, global positioning systems (GPS) and an auto-level were used to quantify stream migration; thermistors were used to record stream temperatures; and a meteorological station recorded daily weather conditions at the ice margin. The gradient of one stream, which was located where the glacier sits in an overdeepened basin, had a gradient of 0.04. The gradient of the second stream, which was located outside of the overdeepened basin, in an area having an extensive joint system developed in the ice, had a gradient of 0.05. Therefore, we conclude the ice-surface slope within the basin is not as great as the ice-surface slope just beyond the margin of the basin. The topography of a 10 m by 50 m area around the second stream was surveyed twice, two weeks apart, to generate topographic maps of stream migration. One crest of a stream meander migrated 94 cm. The measured angle of stream incision into the ice was 26°. A comparison of mapped meanders to nearby joints in the ice show that the stream path tends to follow the joint patterns. The stream cuts through the ice in order to join up with the joints, forming a larger stream by combining with water flowing down gradient along the joints, and then eventually forming new meanders. Variations in the temperature of stream water due to changes in the air temperature are hypothesized to control the rates of stream incision. Stream temperatures showed a daily range of up to 0.2° C.