DEGLACIAL ICE MARGINS IN THE FINGER LAKES REGION OF CENTRAL NEW YORK

Abstract

Recessional positions of the Laurentide Ice Sheet (LIS) margin are generally well defined in western and eastern New York. However, ice margin positions in the intervening Finger Lakes region are less well resolved, with detailed studies in some areas unlinked or only tentatively correlated to the regional situation. This ongoing project is using LIDAR-data to map LIS marginal positions through the Finger Lakes region in a three-step process. First, all available LIDAR data have been obtained for 20 counties in central NY and processed into county-level 2m-resolution Digital Elevation Models (DEMs). Second, ice marginal landforms are being mapped for each county using the 2m-DEMs and derived products (hillshades and slope maps). Third, mapped landforms are being field-checked where possible and reconciled with published studies that include subsurface data. Preliminary results show that there are many more end moraines in this region than have hitherto been recognized. Furthermore, many of these moraines can be traced across the landscape for tens of kilometers, thereby easing the correlation of ice margins between areas. Most ice margins are marked by single crested moraine ridges, and cross-cutting ridges in one area indicate that at least one ice marginal position involved a distinct re-advance. The Valley Heads (VH) moraine system at the south end of the Finger Lakes is distinctly different to moraines farther north. In large valleys it consists of an outer position marked by subdued landforms and subsurface deposits, with higher deposits plus an outwash head generally 2-4 km inboard. The VH position across intervening uplands is either indistinct or is marked by a c.1 km-wide band of hummocky topography. Dead ice landforms are common in large valleys and the VH ice margin is much more digitate than the recessional ice margin positions farther north. Collectively, this VH landform assemblage suggests a surge re-advance to the outer position, followed by stagnation of the outer ice rim with concomitant ice margin stabilization a few kilometers inboard.