LIDAR-BASED LANDSLIDE INVENTORY MAPPING FOR THE NORTHERN PORTION OF THE JORDAN NARROWS 7.5-MINUTE QUADRANGLE, UTAH

Landslide inventories form an essential basis for landslide hazard and risk analysis. Landslides are a recurring hazard on hillslopes throughout Utah, but can be difficult to map accurately in urban areas and densely vegetated terrain. However, digital elevation models of the bare-earth surface derived from Light Detection and Ranging (LiDAR) data express topographic details sufficiently well to map landslides. Landslides were mapped at a scale of 1:4,000 and a landslide inventory was prepared using ArcGIS for the northern portion of the Jordan Narrows quadrangle near Bluffdale, Utah. Landslides and main scarps were mapped using 2-meter LiDAR imagery and checked by conventional aerial photogrammetric methods. High-resolution orthophotographs, in addition to LiDAR derivatives including several variations of hill-shade relief maps having different sun illumination angles, topographic contour maps, and slope gradient maps were used in the mapping process. Each mapped landslide was characterized as to type of movement, slope gradient, movement direction, estimated failure depth, geologic unit, relative age, and mapping confidence. Preliminary results suggest that previous geologic mapping at a scale of 1:24,000 that relied solely on field and photogrammetric methods identified only 19 percent of the landslides mapped using LiDAR. Current mapping indicates that oversteepened slopes above the Jordan River in late Pleistocene Lake Bonneville gravel and sand deposits are prone to landsliding. Results of this landslide inventory will be published as part of a Jordan Narrows quadrangle geologic hazards folio.