PRESERVING THE LEGACY OF LATE WISCONSINAN BREAKOUT FLOODS IN THE CHAMPLAIN VALLEY, NORTHEASTERN NEW YORK

Late Wisconsinan deglaciation of northern New York and adjacent Canada created deep proglacial lakes in the St. Lawrence and Champlain lowlands. Glacial Lake Iroquois occupied the Ontario and St. Lawrence lowlands and drained to the North Atlantic through the Mohawk and Hudson lowlands. Retreat of the Laurentide ice margin from the northern flank of the Adirondack Mountains uncovered a lower threshold near Covey Hill, PQ and Lake Iroquois catastrophically discharged southeastward along the ice margin to Lake Vermont in the Champlain Valley. The proglacial lake in the St. Lawrence Lowland temporarily stabilized at the glacial Lake Frontenac level until further ice recession resulted in its drainage around the northern flank of Covey Hill. The breakout floods stripped large areas of their surficial cover and cut deep bedrock channels and plunge pools into the Late Cambrian Potsdam Sandstone bedrock. The exposed sandstone pavements, known locally as Flat Rocks, occur in a discontinuous, 5 km wide belt that extends more than 30 km southeastward into the Champlain Valley from Covey Hill. Cobblestone Hill, an elongate ridge of large, angular, imbricate sandstone boulders, was deposited along the ice margin where the floodwater entered Lake Vermont. Presently, many of the sandstone pavements are covered by jack pine barrens, a globally rare ecological community.

Preservation of the Late Wisconsinan breakout flood deposits and landforms presents many challenges because the Flat Rocks cross traditional land management boundaries such as watershed divides and local, state and federal political boundaries. Some portions of this landscape have been protected by four separate entities. The New York State Department of Environmental Conservation manages The Gulf State Unique Area as a part of the constitutionally protected New York State Forest Preserve. This site provides public access to The Gulf, a deep channel and plunge pool that straddle the international border. The Nature Conservancy of Canada provides protection and public access to portions of The Gulf on the northern side of the border. The Adirondack Nature Conservancy protects and provides public access to portions of the Gadway Preserve, a jack pine barrens on Blackman Rock. Finally, the William H. Miner Agricultural Research Institute protects more than 1,000 ha of jack pine barrens at Altona Flat Rock.