LONGITUDINAL RIVER PROFILES IN THE CHAMPLAIN VALLEY: WHAT ARE THEY TELLING US?

Channel profiles of rivers in the Champlain Valley may provide clues to understanding the origin of topography in the Green Mountains and Adirondacks. The key goal of this work is to determine whether the location of knickpoints in major rivers draining into Lake Champlain is related either to changes in rock strength or base level changes. The eight rivers compared in this study are Otter Creek, Winooski, Lamoille, and Missisquoi Rivers on the Vermont side of Lake Champlain, and the Ausable, Salmon, Saranac, and Bouquet Rivers on the New York side of Lake Champlain. These large rivers drain directly into Lake Champlain, the regional base level. Knickpoints in these rivers could be indicative of a change in base level due to post-glacial fluctuations in lake-level or to localized glacial erosion in the Champlain Valley. Profiles of the eight rivers were extracted using Digital Elevation Models. Knickpoints in the river channels are identified by the profiles and compared to the local bedrock geology. From this comparison and correlations of knickpoint elevation changes across different profiles, knickpoints are categorized as transient or static. Transient knickpoints move upstream by eroding away the channel, perhaps in response to a lowering of the base level caused by tectonic changes or glaciation. Static knickpoints remain in place over time, perhaps due to changes in lithology from competent to less competent rocks, such as quartzite to limestone. Preliminary results suggest that some knickpoints may be caused by recent diversion of river courses by glacial deposition and erosion. The ultimate goal of our work is to place constraints on the rate of knickpoint retreat and use these rates to better understand the long term erosion of the Adirondack and Green Mountain regions.