Late Wisconsinan ice sheet flow across northern and central Vermont, USA

A compilation of over 2000 glacial striation azimuths across northern and central Vermont, northeastern USA, provides the basis for interpreting a sequence of ice flow directions across this area. The oldest striations indicate widespread ice flow to the southeast, obliquely across the mountains. Similarly oriented striations between northern Vermont and the ice sheet's terminus in the Gulf of Maine suggest that a broad area of southeast ice flow existed at the Last Glacial Maximum. Younger striations with more southerly azimuths on both the mountain ridgelines and within adjacent valleys indicate that ice sheet flow trajectories in most areas rotated from southeast to south, parallel to the North-South alignment of the mountains, as the ice sheet thinned. This transition in ice flow direction was time transgressive from south to north with the Green Mountains eventually separating a thick south-flowing lobe of ice in the Champlain Valley from a much thinner lobe of south-flowing ice east of the mountains. While this transition was taking place yet ice was still thick enough to flow across the mountains, ice flow along a narrow ∼65 km long section of the Green Mountains shifted to the southwest such that ice was flowing into the Champlain Valley. The most likely process driving this change was a limited period of fast ice flow in the Champlain Valley, a short-lived ice streaming event, that drew down the ice surface in the valley. The advancing ice front during this period of fast ice flow may be responsible for the Luzerne Readvance south of Glens Falls, New York. Valley-parallel striations across the area indicate strong topographic control on ice flow as the ice sheet thinned.