ICE STREAMING IN THE SOUTHERN CHAMPLAIN AND NORTHERN HUDSON RIVER VALLEYS, VERMONT AND NEW YORK

Numerous paleo-ice streams have been identified around the periphery of the Laurentide Ice Sheet and their distribution suggests that ice streaming was an on-going process during the retreat of the ice sheet. Several observations suggest that ice streaming also occurred in the southern Champlain and northern Hudson River valleys for a limited period of time during the retreat of the Laurentide Ice Sheet. Ice streams in the Greenland and Antarctic Ice Sheets contain source areas of converging ice flow that feeds these ice streams. Converging ice flow into the southern Champlain Valley is indicated by a set of NE-SW striations along a 65 km reach of the Green Mountain ridge line between Pico Peak and Appalachian Gap that distinctly cross-cut older striations produced during regional ice flow across New England. Most current ice streams are also located in topographic troughs. The Champlain and northern Hudson River valleys form a substantial north-south trough separating the Green and Taconic Mountains to the east from the Adirondack Mountains to the west. Abundant, wide-spread N-S striations in these valleys cross-cut all older striations indicating that ice flow was funneled parallel to this trough. The low surface slopes of modern ice streams suggest very low basal shear stresses facilitated by high basal water pressure and/or weak substrates. Both the Champlain and Hudson River valleys are underlain by relatively weak Cambrian and Ordovician shales and carbonate rocks. Furthermore, bedrock in these valleys was overlain by fine-grained Illinoisan-age glacial lake sediments deposited during the retreat of the previous ice sheet which would have been incorporated into the basal till in these valleys. Highly elongate streamlined bed-forms, similar to those imaged beneath modern ice streams, are clearly visible in the Lidar imagery from these valleys where not masked by younger lake sediments. This ice-streaming event may be responsible for the Luzerne Readvance. The limited areal extent of striations showing ice flow converging into the Champlain Valley indicates that this period of fast ice flow was relatively short-lived.