MULTISPECTRAL IMAGE ANALYSIS AS A GUIDE TO IDENTIFYING POTENTIAL SOIL – BEDROCK KARST COLLAPSE HAZARDS IN URBAN SETTINGS; FARMINGTON, MISSOURI

Catastrophic soil collapses into karst joints have occurred in Farmington, Missouri, sporadically since the late 1960’s. These collapses have caused municipal and residential damage and heighten the potential to pollute groundwater. There are few active, small sinkholes, no known caves, and few bedrock exposures in this low-relief area. Therefore, surface geology and landforms are not good guides to evaluate collapse hazard potential. The circular collapses appear to be centered over solution-enlarged joints in dolomite bedrock, and are generally from 1.5 to 5 meters deep and up to 10 m wide. One collapse centered on a joint overlain by 4 meters of soil, had an open joint 2 meters wide, and was more than 18 meters deep. Soils above open joints are piped from the surface as groundwater is drained at the vertical bedrock joint interface. Shallow groundwater conditions are also thought to be lower near the joints, particular during dry seasons, leading to excessive drying of overlying soils. Dry soils and stressed vegetation therefore, may have a direct relationship to joints that are actively draining shallow groundwater. The vegetation and soil moisture relationships can be observed in temporally appropriate multispectral imagery. Landsat 4 imagery was used to analyze moisture stress in vegetation as a tool for locating potential collapse locations. The imagery provided many areas of moisture stress of which three were chosen for field analysis with electrical resistivity. Two of the three areas proved to have deep joints underlying the areas of moisture stress, however conclusive results are hampered due to spatial resolution of the satellite imagery, size of collapses and the current understanding of the geology in this area.