ANALYSIS OF SUBGLACIAL MELTWATER EROSION IN THE HUDSON VALLEY, NEW YORK

The Hudson Valley of New York was an important glacial throughway from the Great Lakes and the St. Lawrence Valley to the Atlantic Ocean. During deglaciation, large meltwater floods from the drainage of ice-dammed lakes swept through the topographically lowest portions of the valley. The role of earlier subglacial meltwater flows, however, has not been closely investigated. This study approached Hudson Valley subglacial flows through GIS-based modeling of subglacial hydraulic heads, using a DEM base (uncorrected for postglacial changes or bathymetry below lakes and rivers), and superimposing planar ice sheets with systematically varying slopes and flow directions. Results show that subglacial meltwater flow was substantially constrained by major topographic features including the Catskill and Taconic Mountains and largely restricted to the Hudson trough. Modeled meltwater pathways are locally corroborated by field evidence, such as a boulder-strewn channel within the uplands of Harriman State Park. Large crescentic forms, up to several km across and hundreds of meters high, eroded into subhorizontal sandstone and shale of the Devonian Hamilton Group near Alcove Reservoir, are similar to ‘mega-sichelwannen’ described from other glaciated areas. These forms have been interpreted by some workers to be created by meltwater erosion in subglacial megafloods. Associated field evidence for large-scale subglacial meltwater erosion is not obvious, however, and the origin of these features remains unclear. Overall, the subglacial landscape of the Hudson Valley is strongly controlled by bedrock structure and lithology, as eroded both directly by ice and by meltwater.