(WHTM) — Pennsylvania is one of the states most prone to sinkholes, according to the American Geosciences Institute, but where do sinkholes occur most in the Keystone State?

According to the Pennsylvania Department of Conservation and Natural Resources (DCNR), a sinkhole is a depression in the ground caused by the collapse of the surface layer. Sinkholes typically occur naturally due to the physical and chemical weathering of specific types of bedrock.

Still, underground mining and other human activities can speed up the sinkhole process.

The DCNR says sinkholes and caves are a definitive part of Pennsylvania's landscape underlain by limestone or dolostone, also known as karst. While it took millions of years for the landscape to form, these rocks easily dissolved when in contact with natural acids created by mixing water and carbon dioxide.

This dissolving process is enhanced by fractures in the rock, which act as a natural plumbing network. According to the DCNR, acid sometimes acts as a de-clogging agent for said fractures, causing the ground to sink in.

Where there are sinkholes, there is karst. While humans can cause sinkholes in areas without karst, the areas of Pennsylvania with the highest karst features are more susceptible to sinkholes.

According to the DCNR's GEOlogic Data map, the areas with the highest karst features include much of the Midstate. Lancaster, Chambersburg, Lancaster, Lebanon, Altoona, State College, and Allentown have some of the highest levels of surface depression and sinkholes.