Sinkhole Risks: 40% of the Continental U.S. Is Prone to Sinkholes

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If you are visiting this page, you probably want to learn where you are most likely to be swallowed by a sinkhole.

Well, around 40% of the U.S. lie in areas prone to sinkholes.

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Homes destroyed by a giant sinkhole in Florida. Picture via CNN

Imagine your are walking in the street and the ground suddenly collapses under your feet and you fall underground. Or imagine a crater opens up beneath your home or car and you just disappear in it. Just too frightening, isn’t it?

Although sinkholes rarely happen, they will make the headlines as mostly tragedy occurs. So you better know them to avoid them.

What Is A Sinkhole?

Sinkholes are underground cavities or craters that form when water erodes an underlying rock layer.

There are three types of sinkholes:

  • One forms when the roof of a cave collapses and exposes the underground cavern.
  • The second type forms when water dissolves the rock underneath soil and creates an underground chasm.
  • The thrid type are man-made sinkholes, i.e. water main break, poor construction.

How and Where Do Sinkholes Form?

Sinkholes takes place where the underground rock is water-soluble such as, for example, in karst, limestone, carbonate rock and salt beds areas.

Dissolution of this ground creates caverns that will collapse when the underground spaces become too large and cannot support the land surface anymore.

Map of Sinkholes in the U.S.

As shown in this map from the U.S. Geological Survey, U.S. sinkhole risks are the highest in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.

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Karst makes up to 20% of the U.S. geology, meaning those areas are prone to sinkholes in the U.S.. Map via USGS

As shown in the map above, it’s not only Florida that needs to worry about sudden cave-ins and sinkholes. More than 20% of the continental U.S. is built on karst, a water-soluble rock, and is thus prone to sinkhole.

Now if you add salt and gypsum, two other water eroding rocks, more than 40% of the continental U.S. is prone to sinkholes as shown in the map below:

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More than 40% of the U.S. ground is made of water soluble rocks like karst, salt and gypsum and thus prone to sinkholes. Map via USGS

This is completely crazy, isn’t it? 40% of the U.S. underground is susceptible to dissolve in water to form catastrophic sinkholes.

These rock types are evaporites (salt, gypsum, and anhydrite) and carbonates (limestone and dolomite).

Evaporite rocks underlie about 35 to 40 percent of the United States, though in many areas they are buried at great depths.

How To Protect Against Sinkholes?

In Florida and Tennessee insurers are required to offer sinkhole coverage with home policies. If they don’t just ask.

In other states, you have to ask for it to get it. And keep in mind, if you do not have this insurance you are not covered. So if you want such a sinkhole coverage policy ask your insurer.

Lessons to take home: More than 40% of the U.S. is prone to sinkholes, not just Florida! The highest risks for sinkholes are in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. And if you want to get covered against sinkhole damage, ask you insurer. Have a great time and don’t get swallowed by an underground crater.

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22 Comments

  3. What if I know of a place that is about 2 inches round, deep and drinks water? At one time I tried to fill it with dirt but it opened back up and now I think its a little bigger. I noticed it about 30 – 40 years ago.

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  8. I’m thinking of buying property near Granbury, Texas. I’m concerned about the likeliness of a sinkhole in that area.

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