The USGS posed an article titled “The Science of Sinkholes” on March 11, 2013 that discusses various types and causes of sinkholes from a national perspective with a map highlighting areas more prone to sinkhole formation.
A devastating sinkhole occurred in Florida on February 28, 2013, raising questions and concerns about this incredible phenomenon. Around 20% of the U.S. lies in areas susceptible to sinkhole events, highlighting the need for research and to be informed about this hazard.
What is a Sinkhole?
Geologically, a sinkhole is a depression in the ground that has no natural external surface drainage. Basically this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface.
Sinkholes are most common in what geologists call, “karst terrain.” What’s that? These are regions where the type of rock below the land surface can naturally be dissolved by groundwater circulating through them. Soluble rocks include salt beds and domes, gypsum, and limestone and other carbonate rock. Florida, for instance, is an area largely underlain by limestone and is highly susceptible to sinkholes.
When water from rainfall moves down through the soil, these types of rock begin to dissolve and spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a period of time until the underground spaces just get too big. If there is not enough support for the land above the spaces, then a sudden collapse of the land surface can occur.
Keep in mind though that while collapses are more frequent after intense rainstorms, there is some evidence that droughts play a role as well. Areas where water levels have lowered suddenly are more prone to collapse formation.
Areas Most Susceptible
About 20% of our country is underlain by “karst terrain” and is susceptible to a sinkhole event. The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.
To read more from this article please visit USGS.gov
