Abstract

Western North Carolina is prone to landslides under normal rainfall conditions due to the steep topography of the mountains and underlying bedrock structures. However, when a large rain event occurs, it exacerbates this likelihood of landslides. Hurricane Helene impacted the region as one of the deadliest landslide events in recorded history of WNC. At least 2,015 landslides were identified as of March 2025. This study evaluated a section of the Swannanoa Lineament from Asheville to Old Fort, NC to constrain its contribution to landslide occurrences during Helene. This lineament is defined by numerous joints and faults that are part of this brittle fault system. Landslides in this section were identified from the USGS Helene landslide database, from NOAA high resolution imagery collected following the storm, and from field observations. The orientation of the joints, faults, and foliation in the bedrock was then evaluated to see if there was a correlation between their orientations and landslide occurrences. This data was collected in the field and added to existing data provided by the NCGS. The foliation dominantly strikes NE-SW and dips SE whereas the joints dominantly strike NW-SE with a near vertical dip. Of the 129 landslides identified in the field area, a significant number of them were on south-facing slopes. The orientation of the foliation and joints could create wedge slope failures on south-facing slopes which would explain the preference for that direction. The wedge failures can also occur on E-NE facing slopes, which accounts for the second highest occurrences in these directions. The North Carolina Geological Survey has an existing landslide susceptibility map for Buncombe County. This study shows that bedrock failure planes should be considered in susceptibility evaluation.

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