USING HIGH-RESOLUTION LIDAR TO IDENTIFY RELICT LANDSLIDE FEATURES IN THE BLUE RIDGE MOUNTAINS OF CENTRAL VIRGINIA

In 2018, the Virginia Department of Mines, Minerals and Energy – Division of Geology and Mineral Resources, received a 3-year FEMA Pre-Disaster Mitigation grant to conduct landslide hazard mapping in the western portions of Nelson and Albemarle Counties. Located along the eastern slopes of the Blue Ridge Mountains, these counties suffered severe landslide damage due to Hurricane Camille in 1969 and a strong rainstorm in 1995. As part of the project deliverables, our team has expanded a 1999 U.S. Geological Survey landslide inventory using 2016 1-meter resolution LIDAR. This will be the first countywide landslide hazard study completed in Virginia using high-resolution LIDAR. So far, over 850 debris flows and slides have been identified in the study area. We are also using LIDAR to identify previously unrecognized accumulations of hummocky, rocky landslide debris with no clear modern headscarp. These features only appear in areas underlain by the Catoctin Formation, a Neoproterozoic-aged metabasalt unit that forms steep ridges and slopes with thin soils. We have termed these features relict or weathered landslides depending on their geomorphic shape and degree of weathering. The contact between these features and the residual slope is abrupt; the features are recognized in the field by their irregular surface and buried cobble-to-boulder sized debris. These features are of particular interest as they are unconsolidated masses of bouldery material on steep slopes and pose a potential slope movement hazard to structures if they reactivate. Hazard maps developed for this project will identify these relict landslide areas and locations will be made available to local planning agencies, emergency management, property owners and other stakeholders.