Cover-Collapse Sinkholes. A geologic hazard is a naturally occurring geologic condition that may result in property damage or may be a threat to the safety of people. The geologic hazards associated with karst are: sinkhole flooding, groundwater vulnerability, radon, and cover-collapse sinkholes described on this page.
Cover-subsidence sinkholes Cover-subsidence sinkholes tend to develop gradually where the covering sediments are permeable and contain sand. In areas where cover material is thicker or sediments contain more clay, cover-subsidence sinkholes are relatively uncommon, are smaller, and may go undetected for long periods.
Dissolution sinkholes happen slowly and are generally not dangerous, but one that becomes a pond can drain suddenly if water makes it through the protective bottom layer. The second type of sinkhole is a cover-subsidence sinkhole. These sinkholes happen in areas where sand covers the bedrock.