Landslide Soils and Geomorphology in Bridger-Teton National Forest, Northwest Wyoming

Active landslides are evident throughout Bridger-Teton National Forest (BTNF), and northwestern Wyoming has one of the highest landslide densities in the country. Land use changes and increased demands for infrastructure challenge BTNF to better understand landslide processes in order to make informed land management decisions. Despite recent population growth in the region, research on landslide phenomenon is generally lacking. In this study, soil and slope geomorphic properties related to landslide occurrence were studied at 18 landslides in the BTNF. Landslides were categorized as active or inactive based on geomorphic features. Landslide soil characteristics, including texture, shrink-swell potential, clay mineralogy and horizonation, were compared on active and inactive landslides. The results indicate that soil characteristics related to degree of soil formation, including soil organic matter content, horizonation and profile depth, were different on active and inactive landslides. Also, soil characteristics that influence slope stability, including soil plasticity, shrink-swell potential and clay mineralogy, were distinctly different on active compared to inactive landslides, especially in the C horizon of the soils examined. This study shows that certain soil characteristics may be useful tools for assessing landslide frequency. Also, our results support the hypothesis that landslide occurrence in the BTNF is related to geology, and to the weathering of slope material, which effects clay mineralogy.