Sinkholes

Sinkholes

Sinkholes develop from both manmade and natural causes. The illustrations below show us how both occur. Areas with a limestone layer above an impervious igneous or metamorphic rock bed stone layer have a greater tendency to have sinkholes because the sedimentary limestone is susceptible to the acidic erosion of rain water which has absorbed carbon dioxide. 

Naturally Occurring Sinkholes

http://dnr.mo.gov/geology/geosrv/envgeo/sinkholes.htm

Human-Made Sinkholes

http://www.canadiangeographic.ca/magazine/jun14/how-sinkholes-form.asp

Silverman, Jacob.  "How Sinkholes Work"  19 November 2008.  HowStuffWorks.com. <http://science.howstuffworks.com/nature/natural-disasters/sinkhole.htm>  02 May 2015.