Statewide Landslide Program in Colorado

Landslides are a common geologic hazard in the State of Colorado and development in the state is increasingly encroaching upon steeper slopes where risk of such hazards is greater. Colorado's main physiographic provinces include the High Plains, the Southern Rocky Mountains, and the Colorado Plateau, which has resulted in world-class scenery but also highly variable geology, topography, and climate. Such variable conditions can commonly create terrain that is susceptible to slope instability. The Colorado Geologic Survey (CGS) is currently conducting a project to inventory all mapped landslides in a GIS framework. The second phase of this project will be the creation of a statewide map of landslide susceptibility from this inventory and other GIS data sets including mapped geology, classifications of slope and terrain aspect from DEMs, and NRCS soil surveys. This program will update and improve earlier preliminary maps of landslide deposits that were published at a 1:250K scale in 1975. As the CGS is compiling this data, a concern is that a “one-size-fits-all” statewide approach using typical GIS spatial analytical techniques may be too coarse or simplistic to determine all aspects of a terrain's landslide susceptibility at a useful scale. For example, susceptibility judgments must be made for landslide areas in normally non-susceptible crystalline hard-rock terrains that have been locally weakened by Laramide faulting and/or hydrothermal alteration, as well as the Late Pleistocene to Early Holocene climate shift when alpine glaciers melted and left oversteepened and unsupported valley walls. This poster presentation will display the current progress of the Colorado landslide program.