MASS MOVMENT VULNERABILITY IN THE SAN JUAN MOUNTAINS, COLORADO: A PILOT 3-D MAPPING APPROACH

Mass movement impacts lives of humans and their infrastructure. Human endeavors in mountainous areas are at risk to mass movement. Thus, the identification and quantification of risk via assigning mass movement vulnerability probabilities are central in guarding lives, resources and confirming proper land-use regulation and planning. Specific mass-movement processes ranging from debris flows, rock falls, snow avalanches to landslides constantly alter the landscape of the San Juan Mountains. Large-magnitude slope failures have historically occurred in the region. Ordinary triggers comprise intense, long-duration precipitation, freeze-thaw processes, human activity and volcanic lithologies overlying weaker sedimentary formations. Forecasting mass movement is a challenge facing geomorphologists because of its episodic and spatially discontinuous occurrences. Mountain landslides are differentiated as mobile and extensive. We developed a 3-D model for landslide vulnerability employing Geographic Information Systems Technology (GIST).

The study area is eight USGS quadrangles: Ridgway, Dallas, Mount Sneffels, Ouray, Telluride, Ironton, Ophir and Silverton. Fieldwork comprised field-reconnaissance mapping at 1:5,000 concentrating on surficial geomorphology. Potential locations were identified while mapping. Additional onsite investigation and photographic documentation was focused on the identified sites. A GIS module was developed to map risk via employing seven terrain spatial databases: geology, surficial geomorphology, slope aspect, slope angle, vegetation, soils and distance to infrastructure. The GIS 3-D model will help clarify risk zonation and provide a spatial perspective of the landscape to improve landslide prediction in the San Juan Mountains.