ICE MOTION SURVEY AND ANALYSIS FOR THE TERMINAL ZONE OF THE MATANUSKA GLACIER, ALASKA

This paper presents the results of an ice motion survey for the terminal zone of the Matanuska Glacier, Alaska, which was conducted for a three-week period from late June through early July in 2003. The terminal zone of the glacier can be divided into 4 ice zones that are characterized by variations in supraglacial debris cover and crevasse development. They include: the clean-ice zone, transitional-ice zone, debris-covered ice zone, and the vegetated-ice zone. The clean-ice is covered with little to no debris and is densely crevassed. Traversing to the east-northeast, the transitional-ice is covered with a thin layer of debris („T 0.5 cm), and has a relatively flat surface that exhibits long, narrow fractures appearing to be healed crevasses. Farther to the east, the debris-covered ice is typically covered with greater than 10 cm of coarse, angular rock fragments, has a hummocky surface due to differential melting, and is densely crevassed in areas. The northeastern most portion of the glacier consists of stagnant ice that is covered with debris thick enough to support forest growth. Williams and Ferriens (1969) assumed that the western most part of the glacier, i.e. the clean ice zone, was the most active and fastest flowing zone however, this hypothesis has never been tested. In recent years, field observations of ice margin advances have suggested the possibility that the clean ice zone is not the most active area in the terminal part of the glacier; thus this study was conducted. The vegetated ice is known to be stagnant, therefore was not included in this survey. Ice motion was measured using a total station instrument. Ice survey stakes were arranged as square strain nets (one in each ice zone) so that horizontal strain could be measured in addition to horizontal ice speed. The 12 surveying markers of the 3 strain nets were surveyed at approximately the same time each day. A horizontal speed profile was developed for each survey point and averaged to determine the mean daily speed of each ice zone. The mean daily speed for the clean, transitional and debris covered ice zones were 0.537, 0.490, 0.442 m/day respectively. Our results suggest that the clean ice zone is slightly more active than the other ice zones, with the debris-covered zone being the least active of the three. Therefore, our measurements support the hypothesis.