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

Abstract

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 personnel to better understand landslide processes in order to make informed land management decisions. Despite recent population growth in the region, research on landslide phenomena is lacking. In this study, soil and 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 the degree of soil formation are different on active and inactive landslides. Soil characteristics such as plasticity, shrink-swell potential, and clay mineralogy influence slope stability and were distinctly different on active and inactive landslides, especially in C horizons. This study shows that soil characteristics and slope geomorphic properties may be useful for assessing landslide frequency. Our results support a hypothesis that landslide occurrence in the BTNF is related to weathering of soil and unconsolidated material, which affects clay mineralogy.