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A hole lot scarier than they look

Sinkholes can appear any time, anywhere, without warning - a particularly dangerous natural disaster that can't be avoided easily.

Poked by a cosmic finger: the gigantic sinkhole in Guatemala City. Photo: Rex/Keystone USA-Zuma.

As Zoe Smith was getting ready for work in High Wycombe, a Buckinghamshire commuter town north-east of London, she noticed, looking through the glass window of the front door, that her car wasn’t where she had left it. “Oh my, that’s a bit strange,” she said to herself.

“So I went back inside, looked out of the window thinking someone has stolen my car,” she told the BBC. “There was just a crater – at which point I screamed the house down.”

A 4.5-metre-wide sinkhole had opened up in the middle of the night, swallowing her car whole. According to reports, the hole is so deep that the car couldn’t be seen from the edge (at least, from as close to the edge as anyone is willing to go). Zoe and her family are now living at a hotel while surveyors determine if their home is at risk of sinking further.

Sinkholes can make for eye-catching and surreal photos. In Guatemala City in 2010, an 18-metre-wide, 30-metre-deep sinkhole opened up and enveloped a three-storey factory; it looked as if a giant space worm had tunnelled right down through the centre of town. But they are also one of nature’s most frightening surprises.

Sinkholes are caused by slow, inevitable erosion. High Wycombe sits on a stretch of chalk bedrock that dissolves readily in water, causing small holes and caverns to appear underground and into which the surface can, sometimes, fall. Sinkholes usually appear around the world in places that have chalk, limestone or other soluble rock strata, and areas subject to extreme weather events such as hurricanes, which can cause flooding, are especially vulnerable.

A less dramatic, but still deadly, frequent cause is bad plumbing – leaking sewers can erode the soil, causing roads or homes to collapse. This compounds the problem in nations with limited budgets for civic maintenance.

Florida suffers particularly badly from sinkholes. According to the financial intelligence firm CoreLogic, 15,000 holes formed in 2013 across the state. The problem seems to be getting worse, too; half of the sinkholes recorded since 1964 occurred in the past three years – and it is believed Florida’s limestone geology is the cause. Last year in Tampa, 36-year-old Jeffrey Bush was swallowed by a sinkhole while lying in bed at home, making headlines across the world. His body was never recovered.

Some commentators have taken to calling Florida “the Swiss Cheese State”. With residents filing over 6,500 sinkhole claims a year, insurance premiums for homeowners can run to hundreds of thousands of dollars. This in turn has caused a notable slowdown in the recovery of the state’s housing market post-2010.

Not every sinkhole is sinister, however. On the seabed, they can cause “blue holes”, which make for superb underwater diving amphitheatres in the Bahamas. The 352-metre-wide Venezuelan sinkhole Sima Humboldt is so vast, it contains its own forest ecosystem at the bottom separate from the wider jungle above.

In Mexico, one legacy of the asteroid that hit the present-day Yucatán Peninsula and killed off the dinosaurs is the geological features known locally as cenotes – sinkholes in the limestone bedrock that can be over a hundred metres deep, exposing groundwater aquifers below and providing challenging, beautiful locations for cave diving and spelunking.

In the time of the Mayans, cenotes were sometimes dedicated places of sacrifice. Today, Nasa uses the 318-metre-deep, water-filled, thermally heated El Zacatón as a testing ground for robots that will one day explore Jupiter’s icy moon Europa.

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Now listen to Ian discussing sinkholes on the NS podcast: