National Geographic News
A partially collapsed building in Clermont, Florida.

People stop to look at a 40- to 60-foot sinkhole that partially collapsed a building in Clermont, Florida.

Photograph by Gerardo Mora, Getty Images

Jeremy Berlin

National Geographic

Published August 12, 2013

Last night a sinkhole opened beneath a central Florida resort, collapsing one three-story building and pulling another slowly into the ground.

An estimated 35 guests escaped unharmed as the 50-foot (15-meter) wide, 15-foot (4.5-meter) deep crater broke glass, snuffed lights, and shook the ground at the Summer Bay Resort in Clermont, about ten miles west of Walt Disney World.

It's the second time this year a major sinkhole has roiled the region. In late February a mouth 20 feet (6 meters) wide swallowed 37-year-old Jeff Bush as he slept in Seffner, Florida, inhaling his entire bedroom. Five others in the house escaped without injury, including Jeremy Bush, who tried in vain to save his brother.

That tragedy left the community shaken and full of questions. To find out more about how and why sinkholes happen, National Geographic sat down earlier this year with Randall Orndorff of the U.S. Geological Survey.

What is a sinkhole?

A sinkhole is basically any collapsed or bowl-shaped feature that's formed when a void under the ground creates a depression into which everything around it drains. (Gallery: Sinkholes from around the world.)

How many types of sinkholes are there?

There are two basic kinds. One is called a cover-subsidence sinkhole. You find these in places like the Shenandoah Valley, or in sandier soils where you've got a void underground. As the soil above transports itself into that cave in the rock, the ground slowly subsides. So it's not catastrophic. It subsides over time. It could be over years; it could be over hundreds of thousands of years.

The other kind is what we call a cover-collapse sinkhole. This is the one that makes the news. It tends to occur in clay, because clay holds soil together like glue. As with cover subsidence, soil is leaching into a cave below, but it creates a void in the soil that moves upward. You can't see it on the surface. Then, all of a sudden, the bridge over top of that void can't hold anymore and it collapses—just like we saw in Florida last week.

Do any human activities induce sinkholes?

Sure. Sometimes in karst areas [irregular landscapes formed when soluble rocks like limestone dissolve], when you drill a well—looking for water or for mining purposes—as you're pulling water out of the ground, you're lowering the groundwater table. That creates almost a toilet-flushing effect. You're lowering that groundwater level, and the soil that was sitting above just falls out. That's one way.

We also induce sinkholes when we start putting up parking lots and buildings and changing what we call the hydrologic regime. Instead of the water naturally soaking into the ground, it's now running off and being concentrated—being put into the ground at one point. (See "Guatemala Sinkholes Created by Humans, Not Nature.")

Which states, areas, or regions are most vulnerable?

Well, if you're talking about limestone, you're talking about the eastern U.S. Obviously we start out with Florida; almost the entire state can be classified as karst, which means it has the potential for sinkholes.

But then you look at other limestone terrain. So the Great Valley, from Pennsylvania—even eastern New York—all the way down through Tennessee to Alabama is an area that's quite prone. So are the Ozarks of Missouri. And Indiana, and the southeastern corner of Minnesota.

Basically from Oklahoma east is where the rainfall averages about 30 inches per year. And that tends to be a dividing line for limestone. But in the arid environments to the West—like the Black Hills of South Dakota and Wyoming, areas in New Mexico, parts of Oklahoma—you have gypsum, which is another soluble rock. It's a tough rock and fine when it's dry, but it tends to dissolve quite rapidly if a lot of rain runs through it real fast.

And then there's salt, which we've dealt with in Daisetta [a town in east Texas that sits on a salt dome and was the site of a 600-foot-wide, 150-foot-deep sinkhole in 2008]. There was a similar situation last summer in Bayou Corne, in Louisiana—a salt dome that collapsed. And we all know that when you put salt in a glass and you put water in it, the salt disappears because it's soluble.

What about other countries?

Mexico and Belize is a karst area. So are parts of Italy. The term "karst" actually comes from a Slovenian [word and region] called Kras, and that whole area of old Yugoslavia—Slovenia, Croatia—is a major sinkhole zone. Huge areas of China are too. And also Russia. Basically it's all over the world. I'm part of a group that's thinking about putting together a karst map of the world. (Pictures: Sinkhole swallows truck in Beijing.)

What are the warning signs of a sinkhole? Is there any way to prevent one from occurring?

Sometimes there may not be any warning signs. But sometimes there are. Keep your eyes open for fresh cracks in the foundations of houses and buildings. Or if suddenly a door frame is skewed and your door doesn't shut the way it used to. Anytime you see something like that inside the building itself, that can be a warning sign.

Outside around the house or building, on the ground surface, you might start seeing cracks in the ground or little depressions. The soil basically pipes down into that cave. And if there's a small area that starts that way, that may be the beginning of a collapse. Or a tree will all of a sudden start leaning. Don't go right up to it, but see if the tree is leaning because the root system is gone or because the ground around it is subsiding.

As far as prevention, if you're lucky enough to see that there's a void beneath a structure, there has been limited success digging out all the soil and getting down to the bedrock, then grouting it with concrete and putting in a lot of bric-a-brac—large pieces of rock, then smaller pieces on that—to try to mitigate it. But if it's under a building [as was the case in Florida last week), then I don't think you'll have much luck.

What is the biggest sinkhole on record? The deadliest? The costliest in terms of property or infrastructure damage?

As far as collapses, loss of life has tended to be minimal, thank goodness. That's because sinkholes are localized. A lot of the fatal ones I've seen have happened on highways, where people were driving down the road and drove right into them. A lot of people who have died in sinkholes were just standing right there when [the collapse occurred].

The one in Guatemala in 2010—that was just an incredible, incredible hole that looked like it was bottomless. To [geologists], that one is probably one of the more spectacular. Of course, that wasn't in a karst area. That was because a big sewage line, or a big storm drain, was buried quite deeply.

Probably the most spectacular one in the U.S. was the one in Winter Park, Florida, in 1981, where the Porsches [at a local dealership] fell into it and it took up a whole city block. When we scientists talk about spectacular sinkholes, that one usually tops the list. And the Daisetta one in Texas, because that was one of the first ones caught on video—you could watch it happen.

What happens after a sinkhole is done collapsing?

Generally, if you don't do anything with it, the hole will plug itself with soil. But then it's a natural drain, so as it rains water flows into it, and it becomes a natural inlet into the groundwater. Sometimes it'll become what we call an "open throat," where you can see the rock at the bottom, which can be an entrance into the cave system. Depending on the depth of the water table, it can also fill up with water. And then you have yourself a pond.

Is the frequency of sinkholes increasing these days?

The answer is we don't know, because we just don't have enough data. Sinkholes aren't widespread events like hurricanes or earthquakes. They're very localized. A lot of karst areas are agricultural, because they tend to have very good farming soil. And sinkholes happen all the time in farmers' fields.

But there's no national or international sinkhole database. Still, as our population grows and we develop more areas that are susceptible, we seem to be seeing more sinkholes—and more stories about humans being impacted by them.

Fay Berry
Fay Berry

Think man has covered the planet with concrete, drilled for all the stuff we feel is precious or required to run vehicles, taken from the water table because money has stopped many countries from recycling bathing water (desalination should be a must given the circumstances) and now we are amazed at mother nature interfering with what we see as our homes, roads and land. It belongs to the Earth and the Earth has it's own life cycle. We are renting for as long as the Earth lets us, if it has many secret caverns/moving plates and waterways beneath our tiny little existence then there is very little people can do about it. I have always said rocks and stones are one of the most important things in the world and my children laugh at my fascination with them. :)  

Mary Gideon
Mary Gideon

I believe sinkholes have probably been occurring more and more frequently,  in the past century, but we are just now  becoming more aware of what is really happening, in our world,   because technology allows us to see it all,  without government interference.  If you really think about it  not that long  ago  television  was controlled more by people  who  stated  what could be shown to the public. Nowadays, we are more and more able to  discover for ourselves and therefore  we realize and learn things  much more quickly than ever before.

Merrita Lyons
Merrita Lyons

I can see how man's drilling/digging etc. could be a major factor in these sinkholes, but we've only been capable of doing so to such an extent for the past 2-300 years or so. I can't help but wonder then, if social media partnered with modern newscasting could be making them SEEM more prevalent than what has always occurred naturally. I'd be really interested in knowing the story on these major sinkholes way back BEFORE 7 billion people began to watch the 6 0'clock news and surf Youtube!

morgan cadle
morgan cadle

the fact is the dirt goes somewhere wouldn't be worth tracking the locations as there may be under ground caverns or tunnels maybe with different species they could be fractures maybe there is still spaces -isn't it worth exploring not all will just be voids and if they are what gas escapes if it's a question of displacement also maybe underground streams Miami used to have fresh water spring what makes us so sure they don't run from silver spring national park under florida

also an idea i put on the pages of the guardian uk edition yesterday from the time at least i know that it was posted immediately

panofom commented on Communities near energy projects need higher incentives, says Tory MP. 16 Aug 2013 3:58pm

wind turbines would work the fact is if you placed the turbines in a fan or clam shape and just powered the first few rows to create a wind flow that wind generated would power each row creating a domino affect that would turn all the other fans create power to store you wouldn't need to rely on constant wind -just power the first few and the rest will turn creating natural wind power now you could combine this with water cycle replicating by having in front of the fans retention ponds as they are called in the states which you heat so causing more pure water evaporation of slightly saline(the reason for this is that you could use the retention ponds then for fish farming increasing fish stock for consumption and it would ease the need to fish in the ocean also you could grow clams and such) so as you heat the water its evaporated into the atmosphere which is then blown by the fans into a cooling atmosphere -you could also use heaters on the ground to make the water molecules rise faster the faster they rise the faster they condense because of the sudden change in temperature or you could artificially cool them using larger air cooling systems much like the new Dyson house coolers on sale in America -by doing this you would create clouds that could then condense and drop pure water onto the surface of the earth aiding in crop growth so more crops can be grown so food prices drop by increasing foliage growth you can also farm more cows on the land so by increasing all of this a sudden drop in food prices so benefits the whole population and these could be used in areas where there is little rain like africa- haiti and others it would also help cool the planets surface and also create more rivers -the importance of this is the fact that by using purer water it can was excess fertilizers into the oceans that help grow algae and food for small creatures that feed the larger creatures up the food chain it woulds also help the big problem we have with the oceans saline levels (funnily enough NASA was doing saline level tests in the lake worth lagoon last year by where i live in Florida- why is a space agency doing the work in the ocean when surly it would be under a different agency)the excess salt in the oceans sinks to the bottom because it is heavier so settle on the bottom and it's well known that this changes the environment that clams and other plants and animals v=breed in and it is the algae that oxygenates the oceans if you kill the algae much like if you kill plants on the surface o2 levels produced would be less so less o2 means less sea life and the environment they grow in changes -if this happens rapidly then then life does not have the ability to adapt or evolve so species die out also bear in mind that the animals often use electromagnets for guidance this would be disrupted because a change to the oceans would change the way electromagnetic occurs -all living creatures use them including humans we have a great deal of copper and minerals in our bodies ) like i suggested on the USA air force collaboration site you could actually use this to detect life forms in search and rescue if you could find the range of electromagnetic s of humans you could locate them using this even though every bodies is unique because of the effect of mass and formation -no two humans are alike even if clones existed would be different because it would depend on the diet weight and environment.
an interesting problem was suggested in the palm beach post article about waste being pumped in the ocean and then in a torchwood(love dr who and torch wood)-my families from wales and i went to Cardiff university there-didn't complete but had great time show on BBC that there are high levels of contraception and estrogen in the oceans now what affect would these have on fish because they would start to produce female attributes now also could this make creatures a sexual and produce with out mating also if this is evaporated along with water molecules into the air and fall as rain what effect would that have on humans and land animals and insects -it has to have an affect if you change the basic environment the species evolve in a different way

just some thoughts for 10.58am in the morning(friday 16th august)

Amber Petry
Amber Petry

@Mary Gideon The more you look at something the more noticeable it becomes. I agree with Mary. 


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