NATURE AND ORIGIN OF BURIED ICE WITHIN A RECESSIONAL MORAINE, MATANUSKA GLACIER, ALASKA

A recessional moraine near the terminus of the Matanuska Glacier, Alaska displays characteristics of being ice-cored. Data collected by ground penetrating radar (GPR) revealed a continuous layer of buried ice within a portion of the recessional moraine. The stagnant ice is overlain by two to six meters of reworked sediment, initially deposited as the melt-out from the basal zone. A combination of a geomorphologic map of the area and the 3-D topographical surface of the top of the buried ice created with the GPR data provides a detailed picture of the nature of this ice-cored moraine. Field observations of the nearby active ice-margin indicate that deposition of sediment is occurring on the surface of the stagnating ice. The local topography is such that the ice margin is at a lower elevation than the older moraine due to the overdeepening of the glacier. The backwasting of the older, ice-cored moraine produces the sediment flows that run downslope towards the active ice-margin, covering the surface of the stagnating ice. The continual deposition of these sediment flows will significantly reduce the melting rate of the underlying ice. As the ice-margin recedes, the buried ice will be abandoned and stagnant, producing an ice-cored moraine. This study provides a model of ice-cored moraine genesis that could be applied to similar recessional moraines, and demonstrates that GPR can be an important tool to study shallow buried ice.