A GLACIAL EROSION MODEL DESIGNED TO RE-CREATE PLEISTOCENE LONGITUDINAL BED PROFILES FOR THE GILKEY AND THIEL GLACIERS OF THE JUNEAU ICEFIELD, ALASKA

The Gilkey Trench penetrates the western edge of the Juneau Icefield in Southeast Alaska where it is filled by many smaller surrounding glaciers. One tributary, the Thiel Glacier, flows northeast towards the center of the Juneau Icefield before abruptly turning west to join the westward-flowing Gilkey Glacier. This intersection suggests that the Thiel Glacier could have initially flowed radially outward from the Juneau Icefield until it was later captured by the larger Gilkey Glacier.

A mathematical model was created to simulate the development of this landscape through glacial erosion. The model calculates the evolution of the longitudinal profiles of the beds of the Gilkey and Thiel glaciers and assumes that glacial erosion scales linearly with basal slip, which increases with glacier thickness and other factors. Since the current longitudinal bed profiles of the Gilkey and Thiel glaciers are unknown, bedrock elevations are estimated by fitting parabolic curves to valley cross sections using a Digital Elevation Model (DEM). Estimates of Pleistocene surface elevations of the Juneau Icefield are used to calculate past ice thicknesses and hence past erosion rates. These rates were scaled using a multiplier derived from the analysis of tributary glacier hang heights. The model adds bedrock progressively back to the longitudinal profiles of the Gilkey and Thiel glaciers through a series of iterative time steps, re-calculating ice thickness and basal sliding at each step, to recreate longitudinal profiles of the Gilkey Trench area at various times in the past going back 100,000 years or more.

If erosion rates increase with ice thickness, then it is expected that bed of the Gilkey Glacier will rise more quickly than the bed of the Thiel Glacier. The steepness of the Thiel profile as it approaches the Gilkey Glacier will decrease, perhaps until the Thiel/Gilkey confluence resembles a plateau that would indicate conditions necessary for glacier capture.