Types of Sinkholes

Sinkholes have both natural and artificial causes. They tend to occur most often in places where water can dissolve the bedrock (especially limestone) below the surface, causing overlying rocks to collapse.

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.