DEVELOPMENT OF LANDSLIDE SUSCEPTIBILITY MAPS IN COLORADO

The Colorado Geological Survey is developing detailed landslide susceptibility and inventory maps for landslide-prone areas in Colorado. A landslide inventory was created by analyzing 1-m LiDAR, contours derived from DEMs, existing geologic maps, and 1-m digital stereo pairs using photogrammetric GIS software. A confidence value of low, moderate, or high was assigned to each mapped landslide using criteria modified from Burns and Madin (2009). Mapped landslides were field-validated where accessible. Landslide susceptibility maps were developed using criteria modified from Ponti and others (2008) and Wilson and Keefer (1985) in conjunction with slope maps derived from 10-m DEMs and published geologic maps ranging in scale from 24,000 and 500,000. The largest scale available was used as the primary source for mapped geology; data gaps were infilled with successive smaller scale maps. The slope map was divided into 7 slope groups: <5°, 5-10°, 10-15°, 15-20°, 20-30°, 30-40°, and >40°. Each geologic unit was assigned to one of three relative rock strength groups: “A” being the most competent rock types, “B” being moderately competent, and “C” being the least competent and unconsolidated deposits. Intersections between one of the seven slope classes and one of the three geology groups were identified using raster math tools in GIS and assigned a susceptibility from 0-10; 0-5 is low susceptibility, 6-7 moderate, and 8-10 high. The aim of these maps is to increase awareness of landslide hazards in Colorado by providing information to the public, local governments, planners, emergency officials, and the engineering community to ensure Colorado citizens are aware of the risks posed by landslides in this dynamic geologic environment.