CHARACTERIZING RECENT LANDSLIDES IN COLORADO SPRINGS, COLORADO, USING 2-D ELECTRICAL RESISTIVITY IMAGING

Active landslides damage the natural environment and result in hundreds of deaths across the world every year. In the USA, annual landslide activities cause 25-50 deaths and $2-4 billion of damage to the valuable infrastructures and homes. The State of Colorado has been highly affected recently by landslides due to the significant urban development in mountainous areas. In the 2018 Colorado hazard mitigation plan, active landslides in El Paso County were ranked as an extreme risk, and Colorado Springs was identified as the most affected city by active landslides in the county. The western side of the city was established on hillslope areas dominated by unstable shale and landslide deposits, which affected the ground stability and made it vulnerable to landslides. In 2015, a heavy rainfall created three active landslides: Skyway, Broadmoor Bluffs, and Cheyenne Mountain landslides, which destroyed about 30 homes. In this study, the electrical resistivity (ER) method was used to investigate the Skyway and the Broadmoor Bluffs landslides in Colorado Springs to characterize the failure zone and geometry of each landslide, as well as to investigate the moisture content and the interface between the different rock types. Two resistivity profiles were conducted across each landslide revealing that the claystone and the shale layers have a larger thickness and a higher moisture content in the western side of the city which are expected to be the main contributing factors to the recent landslide activity in this area. Hopefully, the created ER models can guide the future land use planning and help mitigate the landslide hazards in Colorado Springs.