A LARGE LATE GLACIAL MELTWATER FLOOD THROUGH THE HUDSON VALLEY, NEW YORK, USA

Two large proglacial meltwater reservoirs, one on either side of the Adirondack Uplands of New York State, discharged into the North Atlantic through the Hudson River during the last deglaciation. Glacial Lakes Albany and Vermont formed in the Hudson and Champlain Valleys on the eastern side of the Adirondacks and drained directly into the Hudson River Valley, while Glacial Lake Iroquois formed in the Lake Ontario/St. Lawrence lowlands on the western side of the Adirondacks, and drained into the Hudson Valley along the southern flank of the Adirondacks through the Mohawk Valley. When the ice marginal retreat exposed a low elevation threshold at Covey Hill, Quebec on the northern flank of the Adirondacks, Lake Iroquois meltwater catastrophically discharged along the ice margin and into Lake Vermont at Altona, New York. This resulted in a series of events. First, the level of Lake Iroquois dropped, abandoning the Mohawk Valley threshold. Second, the catastrophic flood across the northern flank of the Adirondack Uplands scoured a series of channels in the sandstone bedrock and deposited bars of boulders at the distal end where it entered Lake Vermont. Third, while these boulder bars were being deposited, the level of Lake Vermont dropped rapidly, probably from a breach of its threshold in the Hudson Valley. We estimate the drop in Lake Iroquois to be 20 m, resulting in a volume loss of about 550 km³. Cross-section measurements of the catastrophic discharge channel at Altona along with velocity estimates derived from the size of the boulders in the bars suggest that discharge along the ice margin reached 41,000 - 82,000 m³/s. This event would therefore have had a duration of 75 - 150 days. We estimate volume loss from the drop in Lake Vermont to be an additional 115 km³, with a discharge of 9,000 - 18,000 m³/s over 75 - 150 days. The cumulative series of events would have therefore sent a discharge of 50,000 - 100,000 m³/s through the Hudson River Valley and into the North Atlantic. The higher end of this discharge estimate is within the range suggested by models to affect production of NADW and alter regional climate. Radiocarbon ages in the Lake Champlain Valley indicate this event occurred between 11,280 and 10,900 ¹⁴C years BP.