THE SUSCEPTIBILITY OF MASS MOVEMENT IN THE WESTERN SAN JUAN MOUNTAINS, COLORADO: A 3-D MAPPING APPROACH

Mass movement contributes to the evolution of hillslope morphology characterized by the downward displacement of rock, vegetation and/or debris, which poses a potential hazard to human activity in mountainous terrain. Hence, the identification and quantification of risk from mass movement are vital to saving lives, protecting infrastructure and implementing best possible land use practices. The complex-geologic setting and rugged topography of the San Juan Mountains have facilitated the propagation of mass movement in the area. Exceeding failure thresholds for various mass-movement types, can result in potential threats to human life and infrastructure. Climate change and increased human activities are altering equilibrium conditions of remnant ice-contact slope deposits, which potentially can lead to greater frequencies of mass movement in the area. As a result of more people expected in the San Juan Mountains as permanent residents or tourists, a comprehensive contemporary mass movement susceptibility study, addressing risks was needed.

The study area encompasses an area of ~ 1,210 km² as mapped on the Ridgway, Dallas, Mount Sneffels, Ouray, Telluride, Ironton, Silverton and Ophir USGS quadrangles. We have developed a GIS-based virtual 3-D model, which highlights the susceptibility of mass movement in the area. We applied a weighted-overlay method integrating six terrain variables of slope angle, slope length, aspect, geology, vegetation, and soil drainage. This 3-D model was enhanced with a surficial-landform map constructed at a scale of 1:5,000, displaying the occurrence of mass-movement features in the area. Our findings suggest that roads and real property situated in areas highly susceptible to mass movement may experience, damage, closure and destruction. Proposed expansion of towns in the area will increase potential liability. Susceptibility analysis of the 3-D model indicates that slope angle and geology have the greatest extent of relative influence on slope failure. We have implemented a combination of emerging geospatial and visualization techniques to improve landslide prediction in mountain regions. An added benefit of the 3-D model is that it is very beneficial in helping the layperson to visualize spatial location and the extent of potential mass movement in the area.