Abstract

Distribution of drumlins on the Ontario Lowlands and the northern Appalachian Plateau of New York State are utilized in a glaciological model that estimates thicknesses of the Late Wisconsin Ice Sheet along five glacial flowlines over the central section of the Finger Lakes. Dynamics of the model are based upon a force balance approach that incorporates variable width of a flowband, bedslope, radius of curvature, and center of outflow location. Drumlin axes along five hydrostatic isograms were projected northward. Points of axes convergence define the center of outflow in the eastern Ontario Basin. Flowlines along the axial trace of the major Seneca and Cayuga Troughs and bordering interfluves were constructed southward to the Valley Heads Moraine System. Calculation of flowline geometry for any assumed basal shear stress requires neither information on ice temperature nor the flow law of ice. Ice thicknesses for each flow line were calculated for τb values of .5, 1.0, and 1.5 bar. Ice thicknesses at 1 bar range from a minimum of 1,932 m for the Seneca Trough flowline to a maximum of 2,093 m at the Keuka-Seneca interfluve flowline. Raising or lowering τb by .5 bar results in maximum thickness differences of +21% and -26%, respectively.

Simulating ice recession, a series of ice-marginal, terminal positions were plotted for a basal shear stress of 1 bar. These predicted terminal positions agree well with locations of mapped moraine deposits. These probable values of basal shear stress support the presence of glacial flow representative of internal deformation rather than basal sliding. Although recent interpretations of the formation of the Finger Lakes focus on ice streams facilitated by large volumes of subglacial meltwater, our evidence discounts the presence of ice streams and supports the existence of outlet glaciers in the troughs of the Finger Lakes.

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