Characterization and Analysis of the Cedar Pass Landslide Complex, Badlands National Park

Abstract

ABSTRACT The Cedar Pass Landslide Complex is located in Badlands National Park, South Dakota, and has created the need for regular maintenance and repair of Badlands Loop Road (South Dakota State Highway 240), the main highway traversing the park. Although there have been previous studies done in small portions of the complex, there has not been a comprehensive study to evaluate the interactions between smaller landslides and the sensitivity of the landslides within the complex to changing conditions. This study used extensive field mapping and slope stability modeling to delineate the boundaries of landslides within the complex, assess the stability, and investigate the sensitivity to fluctuations in groundwater, reduction in material strength, and erosion within the landslide mass. Results show that highway surface damage in the complex is related to the interaction of movement in both smaller and larger landslides. For instance, damage to the Cliff Shelf parking lot is related to small, destabilized blocks above the head scarp of the larger Prairie Island Landslide located to the southeast. In the Upper and Lower Wedge areas, previously mapped landslides were not confirmed, but highway damage may relate to settlement and erosion of an embankment fill and continued deformation of the massive Cliff Shelf paleo-landslide, which was thought to be dormant until the late 1990s. The overall slow and episodic movement of the landslides observed over the past 30 years may be attributed to dilatant strengthening.