A PALEOLIMNOLOGIC PERSPECTIVE ON RECENT CATASTROPHIC DRAINAGE OF A (POST)GLACIAL LAKE IN THE CLYDE RIVER VALLEY, NORTHEASTERN VERMONT

Numerous glacial lakes temporarily occupied topographic lows during and immediately following deglaciation of the northeastern United States. These lakes typically drained as a result of continued ice-retreat opening up alternative drainage pathways or in response to isostatic rebound and adjustment of drainage divides. The nearly flat valley-bottom of the north-flowing Clyde River in northeastern Vermont is consistent with the past existence of a glacial lake. In contrast to the history of most glacial lakes in New England which drained shortly after deglaciation, Native American accounts suggest that the lake filling the Clyde River Valley may have persisted into the late 18^th century before draining catastrophically. A paleo drainage channel exists above the location where the Clyde River passes through a narrow gorge at the Great Falls, the likely location of the natural dam that impounded the proposed paleo lake. The elevation of this alternative drainage would have established a lake filling the Clyde River Valley from the Great Falls in Charleston south to the Oswegatchie Brook in Brighton and extending west to the drainage divide into the Willoughby River, all of which are consistent with historical accounts of the lake’s existence. To shed light on the suspected existence of this long-lived glacial lake and its recent drainage we collected sediment cores from two in-stream lakes along the course of the Clyde River. Pensioner Pond is located just upstream from the site of the suspected natural dam and would have represented a bathymetric depression within the larger lake filling the Clyde River valley. Salem Lake located is located downstream from Pensioner Pond and the suspected site of the natural dam and would have received input from the drainage of an upstream paleo lake. The sedimentary records from both lakes show a marked transition in the characteristics of recent sediments that is consistent with the recent drainage of the proposed paleo lake and a permanent adjustment to the upstream drainage pattern and depositional processes within each lake.