A sinkhole is the result of erosion of the subsurface. When underground water dissolves carbonate bedrock such as limestone, dolomite, or other soluble rock it creates subterranean passages, cavities and caves. This irregular, subsurface rock topography is known as karst. These voids in the bedrock are inclined to sudden surface collapses (sinkholes). Sinkholes can also occur in areas with soft soil, in mining areas, or where some other subsurface disturbance has occurred.
Human activities which accelerate sinkhole formation
New development demands for ground-water resources
Lowering the water table
Changes in surface water flow
Increased weight from structures upon the cavernous bedrock.
Locating sinkholes and subsidence without digging, probing, or drilling can be accomplished using non-destructive field surveys. The two main methods for detecting sinkholes are aerial photography and geophysical procedures.
Electrical Resistivity mapping is a useful tool in many geotechnical and groundwater investigations in karst areas. It is used to locate subsurface depressions in the limestone/soil interface which can indicate the existence of enlarged channels in the bedrock. Enlarged fractures and conduits provide pathways for the preferential movement of groundwater and contaminants. If the channels draining a depression in the limestone surface are capable of transmitting water and soil particles into the underlying karst aquifer, there is also a potential for the development of a sinkhole collapse. Resistivity has also been used to locate subsurface voids (caves), which can play a significant role in the transport of karst groundwater contaminants and in the development of sinkhole collapses.
