What Causes Sinkholes?

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Yesterday, just a few miles away from The Happiest Place on Earth, inhabitants of a luxury resort in central Florida were uprooted from their idyllic vacations when their plush condominiums collapsed into a sinkhole. In place of the three-story villa, residents were left with a 60-foot crater, 15 feet deep—and a lot of questions. Sinkholes have gulped down suburban homes, cars, and entire fields in the past, but how does the ground just swallow up a building like that?

Some sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can’t take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is notorious for such spontaneous natural disasters. The state has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren’t left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

Sinkholes aren’t uncommon, as about 10 percent of the world’s landscape is composed of karst regions. They are, however, no less dangerous for unsuspecting victims. Even knowing exactly what causes sinkholes, their unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

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August 13, 2013 - 8:30am
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