RISK ASSESSMENT OF A ROCK SLIDE ON THE SOUTHERN SLOPE OF THE SHICKSHINNY MOUNTAIN, LUZERNE COUNTY, PENNSYLVANIA

The southern slope of the Shickshinny Mountain located in Luzerne County, PA, hosts at least thirteen distinct rock slides. One, mostly within State Game Lands Number 224, is approximately 920,000 m² in size and has already interfered with the flow pathway of the Susquehanna River. Last studied in 1989, this slide requires further research to better assess risk to motorists on State Route 11 and impact of subsequent failure on the Susquehanna River. This research looks to concisely characterize the volume of the moved mass by coupling surficial terrain data from Light Detection and Ranging (LiDAR) data with a slip surface determined using geophysical methods, as well as estimate continued activity and movement using dendrochronological studies. Geophysical methods used included two electrical resistivity surveys using a 48-electrode Syscal Pro, and both 1D and 2D multi-channel attenuation of surface waves (MASW) surveys using a 24-channel Geometrics Geode seismograph with 4.5 Hz geophones. MASW techniques were preferred for the site given the seismic noise that came from vehicles on State Route 11 and from training activities at the State Penitentiary across the river from the site. Electrical resistivity tomographic data was processed using ResIPy and the end results had less than 3% normalized error. Both 1D and 2D MASW data were processed using Geometrics MASW software. Based on the geophysical results, the slip surface was inferred to be 20-60 m in depth, exceeding prior estimates of 20-27 m. The total estimated volume is in excess of 20 million m³, exceeding prior estimates of 14-15.5 million m³ from the 1989 study. Unfortunately, the entirety of the Shickshinny southern slope was heavily logged in 1940 after four years of controlled burns, so dendrochronological studies can only explain recent activity. Dendrochronological studies were performed on Black and White Oaks likely deformed by slide activity on the moved mass itself, and of Sweet Birch in exposed scarp areas (Sweet Birch are quick to populate newly exposed areas). Ages of deformation of Oaks revealed localized movements, typically following storm events. By plotting ages of Sweet Birch in exposed scarps against their distance from the moved mass, a modern motion of 10s of cm per year was inferred.