EVIDENCE FOR HOLOCENE LAKE-LEVEL CHANGE FROM TWO LAKE CHAMPLAIN WETLANDS

Sixteen radiocarbon-dated cores from two lakeshore wetlands in Lake Champlain indicate that lake-level has risen in three distinct phases during the Holocene. During phase I (10,000-7,500 yr B.P.), lake level rose rapidly in response to similarly rapid isostatic rebound which increased lake volume by raising the sill controlling lake outflow. This was followed by a stillstand during phase II (7,500-5,000 yr B.P.), most likely associated with glacial forebulge collapse. Renewed isostatic rebound of the sill at a slower rate continued to cause lake-level to rise during phase III (5,000 yr B.P. - Present). It is estimated that lake level has risen approximately 8 meters in the northern end of Lake Champlain in the last 9,300 yr B.P., with a greater magnitude of lake-level rise in the central and southern end of the lake due to differential tilting of the basin. Isostatic rebound has been the long-term control on lake-level change throughout the Holocene, with climate change acting as a secondart control.