Electrical Resistivity Imaging of Recent Landslides in Colorado Springs, Colorado, USA

Abstract

Abstract Landslides can cause significant infrastructure damage and thousands of deaths around the world. Colorado Springs has experienced numerous damaging landslides that have not been previously geophysically investigated due to its geological and climatic conditions as well as increased urban development into landslide-prone areas. In 2015, heavy rainfall caused the Skyway and Broadmoor Bluffs landslides that destroyed 30 homes. In this study, these two landslides were studied using the electrical resistivity method to evaluate the nature of the landslides. Two-dimensional inverse models constrained by geological and borehole data indicate that both landslides occurred within the weathered portion of the Cretaceous Pierre Shale. The depth to the landslide failure surface ranged between 3 to 6 m and 6 to 8 m for the Skyway and the Broadmoor landslides, respectively. Both landslides have characteristics of a rotational-type landslide, but three models (two for Skyway, one for Broadmoor) do not have smooth failure surfaces. The Pierre Shale is characterized by significantly lower resistivity than the overlying clay. This suggests the landslide failure was promoted by high moisture content within the Pierre Shale. Therefore, the Skyway and Broadmoor areas need to be monitored for future landslides during high-precipitation events. Additional geophysical data are needed to fully determine the nature and extent of the landslides in Colorado Springs. Our results present the first subsurface models of the Skyway and Broadmoor landslides. City planners can use these models as critical data for mitigating future landslides, which can be used for future urban development.