RESPONSES TO LANDSLIDES AND LANDSLIDE MAPPING ON THE BLUE RIDGE ESCARPMENT, POLK COUNTY, NORTH CAROLINA, USA (Invited Presentation)

In Polk County, southwestern North Carolina, landslides occur along the Blue Ridge Escarpment, with 400 m of topographic relief and slopes typically >20°. Bedrock is characterized by Late Proterozoic to Early Paleozoic metamorphic rocks stacked in Paleozoic thrust sheets. The North Pacolet and the Green Rivers exploit post-orogenic brittle fractures to form reentrants intersecting the escarpment. On May 18, 2018, ~200 mm of rainfall in three hours along the escarpment triggered >240 debris flows and slides, resulting in one fatality and damage to homes and roads. The State Emergency Operations Center tasked the North Carolina Geological Survey to assess slope stability ahead of search and rescue operations. Experience-based response procedures and uncrewed aerial systems (“drones”) facilitated a rapid hazard assessment, coordinated search procedures, recovery of the fatality; and initial damage assessments from debris flows along a 1 km-long, EW-trending, fracture-controlled Pacolet River Valley. Given the loss of life and destruction from the May 2018 storm and threats to infrastructure, we began mapping in Polk County in 2019. Our iterative use of remote sensing and fieldwork resulted in the field verification of 55% of landslide features. To remotely identify landslides, we used quality-level 1 lidar (>8 points/m²), relative vegetation difference maps derived from Sentinel-2 satellite imagery, orthophotography, and drone-derived orthomosaics and digital terrain models. We identified debris flows, active and dormant and composite debris slides, rockslides and rock falls, and deposits from past landslide activity in a 21.6 km² area concentrated on the escarpment and the reentrants.