It was an unexpected sinkhole-in-one for a claustrophobic Missouri man who was swallowed up while walking on the fairway of an Illinois golf course...
- New York Daily News, 12 March, 2013

The earth opened up behind a one-story home in Florida late last night, swallowing an entire bedroom into a sinkhole - now 100 feet wide - and likely killing one.
- gawker.com, 1 March, 2013

Among the dangers of urban and suburban living, one usually thinks of crime, traffic, and - depending on locale - environmental hazards such as fire, flood, tsunami or volcanic eruption. But people who don't live in seismic zones usually don't think the ground is about to open up and swallow them. That is, unless they live in an area known for its sinkholes.

Location, Location, Location

Sinkhole: also known as a sink, snake hole, swallow hole, swallet, doline, or cenote. What causes a sinkhole? Something called a karst process. A karst process happens when an underground layer dissolves. In other words, there might be acid down there, eating away the ground. If it does so, and a funnel opens suddenly, whatever is on the surface - be it parking lot, house, the 14th golf hole, or a sleeping innocent - can be suddenly dropped an enormous distance.

Sinkholes are found in some places more than others. Florida is infamous for the things. The Florida Geological Survey provides a map of known sinkholes and insists that, although human habitation is accelerating the appearance of these fissures, and 'despite the problems they pose for urban centers, sinkholes are a natural part of Florida's ecosystems'¹. In Florida, the phenomenon is of such antiquity that these depressions sometimes provide such amenities as state parks. Unfortunately, the emergence of a gaping hole in the earth is also hard to predict: the house whose bedroom was swallowed up by a 100-foot (30m) sinkhole in March 2013 had passed insurance inspection five months before. Sinkholes are perfidious.

Sinkholes are a global phenomenon. In 1988 one opened in Norwich, UK, and swallowed a public bus. The disappearing bus uncovered a chalk mine that dated back to the 11th Century. In Guatemala, two huge dolines have opened in the 21st Century, both about 300 feet (91m) deep. Sinkholes can open underwater, as in the Blue Reef Sinkhole in Belize. Mining subsidence can be responsible for sinkholes, as it has been in Oklahoma, Missouri, and Pennsylvania.

Sinkholes can open suddenly and suck down objects, buildings, and people. In 2003, a sinkhole in Lisbon, Portugal, consumed a parked bus. The 2013 Florida event swallowed a sleeping man, who was never found. The filled-in hole became this unfortunate victim's grave.

Epidemic?

The number of sinkhole occurrences appears to be growing, or at least reports of sinkholes seem to be more common. This may have a number of causes, including ecosystem change and land development, but are sinkholes, as some Internet writers claim, signs of looming apocalypse? Those of us who fail to recall anything about sinkholes in the Book of Revelation might prefer to turn to the US Geological Survey for non-tinfoil hat explanations.

According to the US Geological Survey, sinkholes are most common in karst terrain. As the agency's scientists explain, in karst terrain, the rock below the land surface can be dissolved by groundwater in a natural process. Karst terrain is most often limestone, but it can involve other types of soluble rock. Rock types that are soluble include salt beds and dunes, gypsum, limestone, and other carbonate rock. Which explains why Florida gets so many sinkholes.

About 20% of the US consists of karst terrain, which has a lot to do with the frequent reports of outbreaks in Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania, as well.

Can humans cause sinkholes? Yes, say the scientists. Mining can contribute to sinkhole formation. So can leaky faucets². Anything that causes changes in drainage patterns can add to the problem.

An Ounce of Prevention

What can you do about sinkholes? If one suddenly opens under your feet, probably nothing. The golfer in Illinois reported that he had no time to react before he found himself at the bottom of an 18-foot (5.5m) hole. It took his friends 20 minutes to extract him. But there might be something that could be done to avoid finding oneself in the situation in the first place.

The USGS suggest that you:

• Check with local authorities to determine the type of terrain your property is located on. If it's karst terrain, observe any changes in your property over time. If you spot subsidence, call in an expert.
• Note any changes in the community that would affect groundwater levels or aquifers.
• Consult regional maps supplied by your country's geological survey, such as the ones provided by the USGS. The British Geological Survey also has lots of information on this subject.

Will the problem of sinkholes go away if we pass legislation against them? Er, no. Will getting excited and protesting stop the earth from making inconvenient gaps in itself? Not at all. Among the things to worry about at night, this is probably one that isn't worth losing sleep over. Unless you live in a karst terrain, or the factory down the road is messing with your aquifer.

Best to look up the geologists in the morning.