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Sinkhole

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.

Various geophysical investigation techniques can be used in karst terrains including ground penetrating radar, electrical conductivity, electrical resistivity, magnetic field, very low frequency measurement (ELF), gravity field recording and seismic velocity measurements.  Electrical resistivity is a versatile tool that offers the ability to obtain high-density subsurface data quickly and cost-effectively. 

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.