A LARGE LATE GLACIAL BREAKOUT FLOOD THROUGH THE CHAMPLAIN AND HUDSON LOWLANDS, NEW YORK

During the last deglaciation two major meltwater reservoirs formed in upstate New York.  Glacial Lake Iroquois formed in the Lake Ontario/St. Lawrence Lowlands on the western side of the Adirondack Uplands, and drained out the Mohawk Valley through the Hudson Valley and into the North Atlantic.  Glacial Lakes Albany and Vermont formed in the Hudson and Champlain Valleys and drained through the Hudson Valley into the North Atlantic.  As the ice margin retreated from the north slope of the Adirondack Uplands it exposed a lower northeastern drainage route for Lake Iroquois, causing a catastrophic discharge from Lake Iroquois into the northern end of Lake Vermont.  This discharge event formed a series of channels and scoured bedrock exposures in the Potsdam Sandstone between the two lakes.  Ice margin correlation shows that at about this same time the high (Coveville) level threshold for Lake Vermont failed resulting in a rapid lake level drop of about 30 meters to the Upper Fort Ann level, and the Ingraham esker was formed in the northern Champlain Valley.  We hypothesize that the throughflow from the catastrophic breakout of Lake Iroquois caused the failure of the Coveville level Lake Vermont threshold.   The resulting 30 meter lowering of the lake caused the sub-glacial discharge that formed the esker.  Rough calculations from the channel geometry and sediment texture at Altona Flat Rock suggest that the throughflow discharge was at least 22,000 to 37,000 m³s^-1.   We also calculate that at least 115 km³ of water was released from Lake Vermont by the change in level.  Based on an outcrop of the glacial lacustrine sequence that shows this level change was completed within one half varve year, we estimate the discharge from the level change to have been at least 11,000 to 44,000 m³s^-1.   The cumulative effect is a discharge of at least 33,000 to 81,000 m³s^-1 into the North Atlantic through the Hudson Valley.  A core obtained from a small lake that was abandoned by the 30 meter drop in Lake Vermont indicates that this event occurred before 10,900 ¹⁴C years B.P.