DIFFERENTIAL ISOSTATIC REBOUND ACROSS NORTHERN NEW YORK STATE IMMEDIATELY FOLLOWING DEGLACIATION

Before the ice margin retreated from the northern flank of the Adirondack uplands during the last deglaciation, two large pro-glacial lakes were trapped in front of it covering a large region of northern New York State.  Lake Iroquois covered about 43,600 km² of the Ontario and St. Lawrence lowlands west of the Adirondacks and drained through the Mohawk and Hudson River Valleys into the North Atlantic.  Lake Vermont covered about 6,550 km² of the Champlain Valley along the eastern flank of the Adirondacks and drained directly through the Hudson River Valley into the North Atlantic.  Ice retreat from the Adirondack uplands caused the confluence of these two lakes to create a single large meltwater reservoir which discharged through the Hudson River Valley before it was finally drained through the Gulf of St. Lawrence with the onset of the Champlain Sea.  High precision three-dimensional measurements were taken on strandline features from the major levels of these lakes, as well as the initial level of the Champlain Sea.  Rebound curves and isobases were derived from these data for three time periods; 1) the early separate pro-glacial lake phases, 2) the confluent phase, and 3) the initial Champlain Sea phase.  The rebound curves have linear slopes, similar to that reported in the glacial Lake Hitchcock basin (Koteff and Larsen, 1989).  The temporal trend of the isobases suggests that the Adirondack uplands were initially rebounding at a faster rate than the St. Lawrence or Champlain Valleys.  The volume of meltwater trapped in the valleys immediately following deglaciation may have been a significant controlling factor on the initial isostatic rebound rates.