Earth Provides Little Warning Before 'Catastrophic' Sinkholes

Melissa Block talks to Anthony Randazzo, professor emeritus at the University of Florida's Geology department, about the science of sinkholes.

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AUDIE CORNISH, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Audie Cornish.

MELISSA BLOCK, HOST:

And I'm Melissa Block. Late last night in Sefner, Florida, near Tampa, a giant sinkhole opened up suddenly under the home of Jeffrey Bush. The hole measures some 30 feet across. It's at least 20 feet deep. Five people escaped the home, but Mr. Bush was plunged into the sinkhole and is feared dead.

For more on the science of what causes sinkholes, we turn to Anthony Randazzo, who has studied them for more than 40 years. He's professor emeritus of geological sciences at the University of Florida and co-owner of a sinkhole consulting business.

ANTHONY RANDAZZO: Sinkholes are caused by the action of water on rock that is vulnerable to dissolving, like limestone. And so, groundwater in Florida is slightly acidic. It will attack the limestone and dissolve it. The dissolution process is a very, very long process. It takes literally millions of years to result in the dissolution of the limestone to the extent that you create cavities and voids large enough to eventually develop into a sinkhole.

BLOCK: And are sinkholes especially common there in Florida, where you are?

RANDAZZO: Yes, they are very common. Literally thousands of sinkholes form every year.

BLOCK: Typically, with sinkholes, is it a sudden collapse, or is this something that happens more gradually over time?

RANDAZZO: Well, there are two basic kinds of sinkholes in Florida: a subsidence sinkhole that takes a long time to develop. It's a very gradual, relentless process that takes tens, if not hundreds, of years to finally manifest itself into a big hole in the ground. And these are very common and they are the most typical type of sinkhole that people experience in Florida.

The other type of sinkhole is a catastrophic type, a collapse type of sinkhole where you are given very little warning. It can take place over the course of minutes or hours or a few days and the house or anything at the surface will be swallowed up. And those are far less common.

BLOCK: When you heard about this collapse in Seffner, Florida, last night, was there anything distinctive about that situation? Is that an area where sinkholes would typically be known to happen?

RANDAZZO: Well, it happened in an area where there's a high probability of sinkhole formation to begin with, of both types: the subsidence sinkhole, as well as the collapse sinkhole. So it's not at all surprising that this hole opened up.

BLOCK: Are you able to detect sinkholes or the likelihood of a sinkhole in advance? In other words, would there be warning signs for people to look for?

RANDAZZO: There are. In most cases for the subsidence sinkholes, you begin to develop cracks in masonry structures. The ground floor might show some slight tilting. But the catastrophic sinkholes will produce more extreme effects of cracking and ground-tilting or floor-tilting, doors won't open or will get stuck, windows will not be able to open properly. And this occurs very, very quickly, as I said, over a course of just a few hours or a day or two.

BLOCK: And where else besides Florida are places that are especially prone to sinkholes?

RANDAZZO: Well, in the United States it would be places where there is very old limestone near the ground surface. And they would include places like Georgia, Alabama, Tennessee, Pennsylvania, Indiana, parts of Texas and New Mexico just come to mind, Kentucky would be another.

BLOCK: Anthony Randazzo, it's good of you to talk with us. Thank you.

RANDAZZO: You're most welcome.

BLOCK: Anthony Randazzo is professor emeritus of geological sciences at the University of Florida and co-owner of a sinkhole consulting business. He was speaking with us from St. Augustine, Florida.

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