LANDSLIDE IDENTIFICATION USING LIDAR, CACHE COUNTY, UTAH

Cache County, Utah, is an urbanized area on unconsolidated Lake Bonneville deposits at the base of the steep Wasatch Front. Steep topography and loose soil situated near suburban structures creates many landslide hazards. As of January 2020, a landslide hazard map of the county has not been created. This study proposes to identify previously undocumented landslides and more accurately map existing landslides in Cache County using the new 2015-2017 0.5m resolution LiDAR dataset. Slope-shade maps are made with LiDAR-based digital elevation models (DEMs) in Global Mapper. These maps are used to map landslides based on the presence of head scarps, hummocky topography, and toes. Potential landslides are compared to aerial photographs from the UGS Aerial Imagery Collection with sets from 1935-1959, 1960-1989, 1990-Present to determine if they were falsely identified from DEMs and are man-made structures or vegetation. The potential landslides are then compared to UGS geological maps and the 2007 UGS preliminary landslide inventory polygon layer, to identify previously undocumented landslides, and identify map units that are prone to mass wasting. Using these methods, 131 potential landslides have been identified that were not on published geologic maps or the UGS polygon layer. The majority of new landslides are along the Lake Bonneville shoreline in the lacustrine deposits of the Provo formation. This study is currently analyzing the data to determine the approximate age of the 131 new landslides by comparing them to aerial photographs, published geologic maps, and published reports. In addition to the new landslides, 40 previously mapped landslides have been more accurately mapped.