THE ROLE OF BEDROCK STRUCTURES IN LARGE SCALE WEDGE FAILURE IN ANDY COVE, PISGAH NATIONAL FOREST, NC

Recent landslides, since 1990, in the Blue Ridge Mountains of western North Carolina have been responsible for the destruction of over 27 homes, the damaging of over 42 houses and 79 roads and the death of six people. According to field investigations conducted by the North Carolina Geological Survey (NCGS), most of these coincided with periods of heavy rainfall associated with tropical storms Frances and Ivan (2004) and Cindy and Ernesto (2005). Andy’s Cove in Pisgah National Forest, North Carolina, is an area of particular significance as it contains three major scale landslides, one of which is one of the larger landslides documented in western North Carolina. Geologic mapping in the field and from high-resolution LiDAR data combined with slope stability analysis was used to determine which structural features contributed to these failures and identify other locations in the cove that are at risk. We found that the dominant foliation (S1) strikes NE and dips SE, consistent with previous studies. S1 is overprinted by S2 which also strikes NE but dips steeper toward the SE than S1. Joints that cut through the foliations have a wide range of orientations but dominantly strike NW/SE. These data suggest that the landslides were produced by wedge failure along S1 and S2, with movement parallel to the strike of the joints. One of the landslides had a significant amount of weathering along the joints, exposed at the head scarp suggesting that weathering along fractures contributed to its large scale. Offset crustose lichen and hockey stick trees suggest movement is ongoing. This study shows the importance of bedrock mapping in assessing the risk of bedrock rooted mass movements in western North Carolina.