UTILIZING LANDSLIDES IN LAKE CHAMPLAIN AS PALEOSEISMIC AND PALEOHAZARD INDICATORS

Lacustrine landslides have been identified in Lake Champlain via Multibeam and CHIRP (compressed high intensity radar pulse) seismic profile imagery. Previous studies have shown that several of these landslides are coeval and occurred ~4500 – 5500 cal yr BP. This study focuses on a series of four overlapping landslide deposits in an area between the Bouquet River Delta and Essex, NY on the western side of the main section of Lake Champlain, where nearly the entire slope has failed, with the exception of a few locations where blocks of slope sediment remain intact. Utilizing Pb²¹⁰, Cs¹³⁷, and C¹⁴ dating on cores from the unfailed slopes, sedimentation rates were determined and showed a higher rate in this region of the lake than the Main Lake, most likely due to sediment flux from the Bouquet River. Using sedimentation rate range of 0.13-0.17 cm/yr and the thickness of sediment accumulation above failed material in seismic imagery, approximate failure ages have been calculated for each of the identified regions on the west side of the study area.

The northernmost failure occurred about 950-1200 cal yr BP, and was the first mass wasting event of this age to be recorded on Lake Champlain. All three of the other regions experienced slope failure about 4500-5200 cal yr BP, and these failures appear coeval with previously studied landslides within Lake Champlain. In the nearby Western Quebec Seismic Zone (WQSZ), clusters of terrestrial landslides have occurred about 1000 and 5000 cal yr BP, and have been associated with seismic events around the date of failure. In particular the 5000 cal yr BP event has been attributed to a M 6.4 or greater earthquake within the WQSZ. The landslides observed in Lake Champlain occurred along the same regional sediment interface, and were likely triggered by these same earthquakes.

Using COMCAT modeling, a lake tsunami model was generated for the 5000 cal yr BP event having 6 failures occurring simultaneously. Depending on proximity to the landslide, results show that portions of the Lake Champlain shoreline could be inundated by waves as high as 5m within minutes of failure.