STRAIN NET ANALYSIS OF THE WESTERN TERMINUS REGION, MATANUSKA GLACIER, ALASKA

The Matanuska Glacier's ice surface in the western terminus region is characterized by varying thicknesses of supraglacial debris. The thickness of supraglacial debris can be categorized into four distinct “zones.” The clean ice zone is characterized by 0-1mm of debris cover. The semi-debris-covered zone has 1 mm to 5 cm of debris cover. The debris-covered ice zone has 5 cm- 25 cm of sediment on the surface. The forested ice zone has debris-cover in excess of 25 cm and supports a spruce forest. The thickness of debris-cover has been hypothesized to reflect the ice surface velocity (Williams and Ferrians, 1962) and the stability of the ice surface, as it relates to vegetation succession (Gilcrist et al., 2002). To further test these hypotheses, we examined the deformation of the ice surface within the clean, semi-debris-covered and debris-covered zones. Three strain nets were constructed approximately 500 meters from the margin of the glacier. The strain nets were 50 meters by 50 meters and located approximately 300 meters from each other within each respective zone. Measurements during June and July of 2004 were taken with a Total Station and prism to accurately measure changes in distances across each strain net.

Analysis of these measurements showed that the ice margin is currently advancing about 3 meters per year, but little to no change in horizontal or vertical distance across any of the strain-nets was detected. Compounding factors that may have influenced this result include: the close proximity of the strain nets to the ice margin lessened the amount of surface strain, human error during surveying obscured a strain record, the size of area covered by individual strain nets inhibited our ability to detect strain, and the duration of the survey period was insufficient. Further research using aerial photographs to construct structural maps of the crevasse patterns near the terminus is ongoing. We anticipate that this approach will be more effective at determining stress fields because it will increase the duration of the study (photographs from 1997 and 1999 will be compared) and increase the scale of observation.