LAURENTIDE ICE SHEET FLOW ACROSS THE CENTRAL GREEN MOUNTAINS, VERMONT

Across most of Vermont glacial striations and erratic fans indicate that the Laurentide Ice Sheet, when thick enough to bury the underlying topography, flowed from northwest to southeast obliquely across the north-south trending Green Mountains, part of the general southeasterly ice flow across New England. However, striations along a 65 km portion of the Green Mountains extending from Appalachian Gap south to Sherburne Gap, indicate that ice sheet flow abruptly changed during ice retreat and flowed from northeast to southwest across the mountains in this restricted area. Extending work originally completed by Ackerly and Larsen (1987), striations have been measured in more than 700 locations along ~100 km of the Green Mountains from Fayston to Ludlow, Vermont. Field work has shown that the southwestward ice flow across the mountains and into the Champlain valley did not extend any farther south than Sherburne Pass (a short distance north of Pico Peak at the latitude of Rutland, Vermont). The elevation of the southernmost southwestward-trending striations, occurring about 1 km south of Sherburne Pass (~43.65°N), indicates that the ice sheet was ~900 m thick in the Champlain Valley when it began flowing southwestward into the Champlain Valley. Peaks lacking southwestward-trending striations have been used to constrain the ice sheet profile to the north. Preliminary calculations indicate that the ice margin lay a few kilometers north of Glens Falls, New York when the ice sheet switched direction and began flowing into the Champlain valley. This ice margin position corresponds to or shortly after the 14.7 ka Luzerne Readvance (Ridge, 2012). The abrupt change in ice flow may be a response to a rapid drawdown of the ice surface elevation in the Champlain Valley possibly due to the Luzerne Readvance or to a rapid calving event in the northern part of Glacial Lake Albany.