Keene Valley Landslide

Laura Sherrod - 2011

The largest landslide in New York State history began in early May 2011.  Melting of heavy winter snowpack followed with abnormally high amounts of April rain saturated the subsurface glacial stratigraphy and initiated the 82-acre slide landslide on Porter Mountain in the High-Peaks region of the Adirondack MountainsDownslope soil movement rates between 15 and 60 cm per day have shown their destructive capacity as the shifting soils have caused one house to be condemned due to the unstable ground under the foundation. At the same time, three other houses were in immediate danger. Dr. Andrew Kozlowski and Dr. Brian Bird of the New York State Geologic Mapping Program, invited a group from Kutztown University (Dr. Laura Sherrod and two undergraduate researchers - Kenneth Schlosser and Jarred Swiontek) to participate in the examination of this landslide.  Geophysical methods were employed to map the glacial deposits in three dimensions to better understand the mechanisms driving this landslide.

Keene Valley

View of the landslide from across the valley - note the small scarp to the right of the pine tree at the left

Condemned House

Condemned house with foundation on the developing scarp with Jarred Swiontek (left) and Brian Bird (right).

The bedrock in this area is believed to be anorthosite which underlies a surficial lithology of glacial sediments. Depth to the bedrock was measured at 76 m in a borehole at the base of the slide. However, in a well near the top of the slide, depth to bedrock was measured at 6 m, with some exposures of bedrock visible at the surface.  Several homeowners are considering moving their homes from their current foundations to alternate foundations.  The topography of the bedrock is particularly important for such an expensive move. 

To delineate three-dimensional trends of the bedrock in the subsurface, several of the geophysical surveys followed the surface exposures of bedrock to a depth where these features were no longer detectable. Nineteen resistivity surveys were implemented to map the subsurface glacial features and depth to bedrock using a MPT DAS-1 Electrical Impedance Tomography System. GPR profiles, using a SIR 3000 GSSI radar system with 100MHz antennae, were collected along many of the resistivity lines and through reconnaissance lines in several other locations (e.g. along roads). Surveys identified features such as the surface of the bedrock, clay and sand layers, and depth to the water table.

GPR Survey
GPR survey with Andrew Kozlowski (left), Kenneth Schlosser (center), and Jarred Swiontek (right)
Resistivity Survey

Resistivity survey line with Jarred Swiontek.

The results of the geophysical surveys are currently being analyzed to develop a three-dimensional image of the subsurface glacial stratigraphy.  Preliminary analysis indicates that there is good correlation between the data sets (well borings, GPR, and resistivity).  Additional geophysical data from seismic surveys and geophysical well logs will be incorporated into the final analysis.  More to come as results are analyzed . . .
Results published in Journal of Environmental and Engineering Geophysics, September 2014
Keene Valley Landslide Results
Geologic Mapping Ground Penetrating Radar
Sherrod Home Page Environmental Geophysics and Hydrogeology Resistivity