Using lidar-derived imagery to reevaluate the landscape of the Appalachian Valley and Ridge

In the mid-1980s, Art Schultz (USGS, ret.) drew on experiences in the Colorado Front Range to identify numerous large, stratigraphically intact, kilometer-scale bedrock landslides on interbedded sandstone-shale dip slopes in the Virginia Valley and Ridge. The physical scale of the slides, along with the thick forest cover, made slide identification challenging, as slides could easily be mistaken for compressional fold-thrust features detached in shale horizons. As a result, the distribution and extent of blocksliding could not be fully evaluated at the time. Revisiting Valley and Ridge slopes with newly available 1-meter lidar datasets highlights the ubiquity of dip slope failure in the central and southern Appalachian Valley and Ridge, with many slides showing morphological features that imply relative youth. In addition to translational blockslides, lidar-derived imagery reveals numerous sackungen in rugged topography developed on gently dipping, interbedded sandstone-shale ridges. Abandoned late 19th and early 20th century iron mines on intact slopes in the vicinity of large blockslides show deep-seated slope movement almost certainly related to mine excavations. The extent of these movements relative to excavation size suggests that caprock-supported rugged topography in the Valley and Ridge may exist at or near the mechanical limit of weaker strata interbedded within the caprock interval. Lidar-supported investigation of Valley and Ridge bedrock slope movements invites reflection on the interpretive skill of Schultz and collaborators and a reconsideration of how potential slope behavior may impact infrastructure in the region.” Prince (2023) Blockslides, summit grabens, and collapsing highwalls of the Appalachian Valley and Ridge: Using lidar-derived imagery to reevaluate a thoroughly studied landscape, USGS Landslide Hazards Seminar, 18 January 2023. USGS Video: https://cms.usgs.gov/media/videos/blo...