Just before midnight one February evening, a giant hole in the earth swallowed Rachel Wicker’s brother-in-law, Jeffrey Bush. His body was never found.
Had she known what was about to happen that night, Rachel and her family would have moved out of the house years earlier, she explains in a new NOVA documentary, which is how we learned about her story.
But she had no idea that their modest Florida home was sitting on top of a ticking time bomb — a sinkhole that would change their lives forever.
While Florida has a reputation for sinkholes, they happen all over the United States and all over the world, often suddenly and without warning, the NOVA premiere (“Sinkholes—Buried Alive”) explained.
The events that precede a sinkhole are subtle, which is why they often go unnoticed.
In the case of Jeffrey Bush, what likely happened is some variation of the following:
Rainwater seeps inside a tiny crack in the ground to the sediment beneath. As more rain pools inside, the water begins to carve out hollow opening deep inside the earth underneath the ground’s surface.
Above the widening gap under the ground, sticky, clay-enriched soil will keep the earth together so that, even as the ground beneath starts to open up, the surface remains superficially strong. In these types of situations, it’s tough to notice that anything’s changed.
But the void underneath begins to swell, growing larger and larger. Suddenly, often without notice, it gives way.
This is a cover collapse — and it’s the most dangerous type of sinkhole. These kinds of sinkholes typically take place in areas where limestone or other types of water-soluble rock makeup a primary component of the underground sediment. Because liquid passes through limestone so easily, it is particularly vulnerable to getting worn away by rainwater.
What happened to the Bush family is rare, however. Most of the time, sinkholes give way gradually, and loose, clay-free soil above the widening gap begins to creep into the hole. Slowly, the ground above begins to sink, forming a bowl-shaped depression in the earth.
If the causes of sinkholes seem entirely natural, it’s important to keep in mind that there are several human activities that can turn a pending threat into disaster.
One of them is salt mining.
Although most American salt mines were built more than a century ago, we still use them to get the ingredients for everything from table and rock salt to chorine gas, a key component of plastic.
The problems start when mining companies send drilling pumps into ancient salty seabeds, pillar-like formations that form over millions of years as surrounding sediments propel them upwards. The pumps dissolve the salt into a salty brine, creating a big watery cavern around the pillar.
If the cavern gets too close to a sinkhole, soil from the sinkhole leaks into the saltwater cavity, causing the ground above to collapse.
In Bayou Corne, Louisiana, a massive sinkhole opened up when an underground gap in the earth collided with an expanding salt mine, swallowing trees and land. Residents were forced to relocate. As of Oct. 2014, the sinkhole continues to spread.
In this 2013 video, the Bayou Corne sinkhole swallows up trees in seconds:
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