Basal Ice in High Arctic Snowpacks

In late May or June, meltwater percolating through cold arctic snowpacks often refreezes as ice layers. In the presence of a cold substrate, such layers form at the base of the snowpack. This basal ice continues to grow so long as meltwater supply is sustained and the substrate remains below 0?C. Upon exposure, the ice is destroyed by sublimation and surface melting or by thermal and mechanical erosion by water which runs on, in or under the ice. Multiyear ice is preserved when the incompletely melted basal ice is buried by subsequent snowfall or by a layer of earth materials. Multiple freezing and melting of water in basal ice layers complicate the snowmelt-runoff relationship in three principal ways. Where basal ice is abundant, the melt is prolonged and contributes to streamflow during the drier summer months. During breakup, the basal ice in stream beds tends to increase flow velocity and, consequently, the capacity for sediment transport. However, a basal ice layer in the channel will reduce opportunities for erosion.