First it was a sinkhole opening under a Corvette museum with a taste for rare cars. Now, it's a sinkhole opening under an active road in Russia, gaping open to gobble commuters. What gives with the car-hungry holes? It's a combination of limestone, water, and bad luck.

Attempts to retrieve sports cars from a Winter Park, Florida sinkhole in May 1981 were unsuccessful, especially as the sinkhole grew to eat more. Image credit: AP

Sinkhole under a busy road Tyumen, Russia. Extracted from video.

Sinkholes happen when water eats away at limestone or dolomite to create a cavern that eventually collapses. What gives with this year's surge of sinkholes trying to eat cars? Bad luck, mostly.

A sinkhole that ate several rare cars under a Corvette museum may be the most expensive sinkhole per square meter of any recorded event. Image credit: National Corvette Museum

We can't currently predict exactly where a sinkhole is about to open up, but we can identify terrain susceptible to sinkholes. They happen in places riddled with caves and caverns, erosion etching through the rock until only thin layers remain. A tiny bit more erosion or a slight change in pressure is all it takes for the ceiling to collapse.

Sinkhole lakes near Winter Haven, Florida. Image credit: Spechler/Kroening

Sinkhole in Oman. Image credit: Hendrik Dacquin

Sinkholes happen in karst terrain. These are the same places we find disappearing and reappearing streams, vertical shafts, caves, flutes, limestone pavements, and poljes. Karst terrain that's been exposed to the elements long enough starts looking like an egg carton, with a few isolated karst towers in a sea of valleys. If you come across ground that seems littered with holes, where the streams seem to disappear and reappear at random, and has tourist signs for cool caves to explore, you're in karst terrain.

The entrance to Škocjan Caves is surrounded by a landscape littered with sinkholes, basins, and vertical shafts. Image credit: Dennis Tang

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Limestone is a soft sedimentary rock formed of calcium carbonate. Limestone can be classified all sorts of fancy ways, but in the over-simplified hand-wavy approach to the universe, limestone is a rock made from old seashells. Every tropical paradise with beautiful reefs and white sand beaches is loaded with carbonate grains just waiting to be lithified into a limestone. It erodes easily in water, or bubbles vigorously when exposed to even weak concentrations of acid. Acid rain is a downright nightmare, etching rock into elaborate, fragile, hazardous landforms.

Egg-carton terrain of karst mountains near Yangshuo, China. Image credit: David Spencer

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Karst terrain is often undercut by complex drainage patterns as water disappears underground, weaves around eroding caves, then suddenly pops back up to the surface. The dissolved minerals can precipitate out of the water, forming beautiful stalactites and stalagmites that will be eroded again.

Karst Spring near Ouhans, France. Image credit: RKraasch

This amazing water mobility means that karst aquifers are astonishingly productive, but also extremely vulnerable to contamination due to the interconnected fissures and fractures. Contaminated surface runoff can disappear underground, travel through well-worn passages, and reappear at the surface in a spring without ever being filtered through layers of sediment and gravel. Within the United States, roughly 40% of groundwater used for drinking water is from karst aquifers.

Carlsbad Caverns contains picturesque example of mineral precipitation features. Image credit: Daniel Mayer

So, why not just avoid building on karst? It's everywhere. A few karst terrains are famous: Florida and Kentucky have made the news with sinkhole-catastrophes, while Carlsbad Caverns and Mammoth Caves are equally well-known for their stunning beauty. But most karst terrains don't show up in the news, and might not even be familiar to the people who live on them. About 20% of the land surface within the country is classified by the US Geologic Survey as karst terrain. We aren't the only one with a sudden-sinkhole problem: China, Europe, the Caribbean, and Australia all also have large areas of karst within their borders.

Areas prone to sinkholes within the contiguous United States. Image credit: USGS

While it seems like sinkholes are everywhere, your chances of being gobbled up by a sudden hole opening below you are slim. It happens — I feel like a story comes out of Florida every year of another home disappearing into a growing hole — but by using geophysics we can actually identify voids before they collapse. Once identified, we can take some small steps to mitigate the problem. But for you, personally, preparing for a sinkhole is a bit like preparing for a landslide: once you know you're in hazardous terrain, you can't do all that much but pay attention and have quick reflexes.