MULTITOOL GEOPHYSICAL ANALYSIS OF GLACIER MARGIN DYNAMICS, MATANUSKA GLACIER, ALASKA

Understanding the dynamic processes at glacier termini is important in developing models of landform genesis. In addition, a better understanding of today’s processes may improve our ability to use glaciers to monitor climate change and to model sedimentation in glaciated landscapes for environmental site characterization and ground-water resource management. The processes resulting in pitted outwash plains remain poorly understood, particularly those of ice burial and melting. This study employed seismic reflection & refraction, ground-penetrating radar, and resistivity techniques to image the extent of buried ice within the proximal outwash plain of the Matanuska Glacier, a temperate valley glacier located approximately 160 km northeast of Anchorage, Alaska. Prior geophysical work has focused on the thickness and geometry of active ice near the terminus; however, very little has been done to determine the subsurface geometry of sediment and the extent of buried ice adjacent to the terminus. Data were acquired in October and December 2000, on the outwash plain proximal to the most active section of the glacier terminus. Thermokarst sinkholes and mid-stream discharge fountains located tens of meters in front of the active margin indicate substantial buried stagnant ice with a persistent conduit system acting as part of the larger subglacial system. Geophysical data reveal relatively continuous sheets of buried, stagnant ice up to 30-m thick within the outwash that are organized as a series of upglacier-dipping imbricated "thrust sheets."

Figure 1. A Typical seismic shot gather showing complex reflections (left) and a stacked section showing the interpreted stacked sheets of buried ice within the outwash (right).