THE 2011 KEENE VALLEY LANDSLIDE: A COMPLEX, DEEP, ROTATIONAL FAILURE IN THE ADIRONDACK MOUNTAINS OF NEW YORK STATE
The spectacular scenery of the high peaks in the Adirondack Mountains occurs as a result of the erosional resistance of the Precambrian Anorthosite bodies that comprises the bedrock. These mountain peaks and adjacent valleys have experienced multiple glaciations and thin glacial soils less than a few meters thick were previously thought to cover the mountain side as discontinuous patches resulting from the Adirondack Lobe of the Laurentide Ice Sheet during the Late Wisconsin.
Preliminary assessment of the trigger mechanism for the landslide is excessive groundwater combined from melting of extremely heavy snowpack combined with excessive April precipitation. The final tipping point came from heavy rains that spanned the last week of April into the first week of May. The excessive groundwater combined with complex glacial soils consisting of interbedded glacial lacustrine clay and silt deposits in excess of 25 meters thick draped on steeply dipping buried bedrock surfaces at high elevation. These glacial deposits were previously unmapped or unrecognized in this region.
The New York State Geological Survey (NYSGS) has monitored movement, mapped the landslide extent, conducted geophysical surveys and exploration drilling to characterize the geology and to evaluate additional hazards. While far from complete the rapid response and near constant monitoring of the still active landslide indicates that due to the geology a continued threat is very possible. Further, our characterization efforts combined with additional field time in the region has made it clear to us that that a continued risk of large landslides in the region is a very real threat to citizens, municipalities and infrastructure.