The science of sinkholes: How heavy rain, drought can help trigger the dangerous phenomenon

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About 20 percent of the United States is more susceptible to sinkholes than the rest of the country.

Sinkholes can be man-induced or natural, AccuWeather Meteorologist Jim Andrews said. Weather extremes such as heavy rains or drought can lead to sinkhole development.

"Man-induced sinkholes typically involve collapse of old mine workings, drainage infrastructure or other underground workings. Naturally, such can fail over time, and rainfall can be a major factor," Andrews said. "Extremes of rainfall, both above and below normal, can be a factor in activating existing sinkholes. These can disrupt the water table, up or down, while also dislodging the loose material covering openings in the limestone."

Cars swallowed by a sinkhole that occurred after a water main break in Bladensburg, Md., Tuesday, Jan. 27, 2015. A water main break caused a sinkhole in a suburban Washington, D.C. neighborhood, swallowing up a family's car just after they escaped in Bladensburg Maryland on Tuesday morning. (AP Photo/Jose Luis Magana)

The most damage from sinkholes occurs in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania, according to the U.S. Geological Survey.

Natural sinkholes are almost always formed in limestone bedrock, Andrews said.

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"Limestone is slightly soluble in acidic groundwater [owing to organic matter as well as acidic rainfall]. Over vast spans of time, limestone bedrock can become riddled with openings dissolved out by ground water flowing to the water table," Andrews said. "Some openings become the caves, great and small, that we are all familiar with. The groundwater carries away the dissolved calcium carbonate that is the essential mineral in limestone."

An overburden of soil and other loose material normally covers the bedrock undergoing dissolution, Andrews explained.

"Inevitably, this loose material will find its way into the bedrock openings, hiding them from sight. Once the void exceeds certain limits, a significant collapse of material into the void can happen, resulting in the surface disturbance we know as a sinkhole," Andrews said. "Over geological time, landscapes on limestone bedrock develop distinctive character shaped by dissolution and collapse. This is known as Karst; there are often pits with permanent or temporary ponds/lakes."

This image made from video provided by the Hillsborough County Fire Rescue, shows the property where a sinkhole reopened, Wednesday, Aug. 19, 2015, in Seffner, Fla. The sinkhole reopened in the exact same location where one swallowed a man as he slept in his bed more than two years ago.  The new hole is 17 feet wide by 20 feet deep,according to code enforcement director Ron Spiller.  (Hillsborough County Sheriff's Office  via AP)

An engineer surveys in front of a home where sinkhole opened up on Friday, March 1, 2013, in Seffner, Fla.  A man screamed for help and disappeared as a large sinkhole opened under the bedroom of the house, his brother said Friday. The brother told rescue crews he heard a loud crash near midnight Thursday, then heard his brother screaming. The brother called police and frantically tried to help. An arriving deputy pulled him from the still-collapsing house. There's been no contact with the man since then, and neighbors on both sides of the home have been evacuated. (AP Photo/Chris O'Meara)

Warm, wet climates cause the fastest dissolution of limestone bedrock and this is where Karst, with its natural sinkholes, is best developed, Andrews said. However, Karst can even be found in deserts, where it is likely be a leftover from a "fossil" wet climate, long-ago turned dry.

Active sinkholes can be relatively small, a few feet, or they can measure many tens of feet across/deep, depending upon how big the underground void was and how much material flowed into it.

"Anything of importance above the collapse can be drawn into it. The bigger the sinkhole, the greater is the risk of property loss," Andrews said. "New sinkhole collapses usually involve existing sinkholes; these may or may not have been known to exist before collapse."

A new sinkhole collapse involving an existing sinkhole occurred in August of 2015 when a sinkhole opened up in Seffner, Florida, two-and-a-half years after the initial sinkhole swallowed up part of a house, killing one man inside.

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