The untold truth of sinkholes

There are plenty of things to be afraid of, like your family getting a good, long look at your internet history or sitting in an Alabama jail for illegal use of confetti. If there's anything we'd like to think we can count on to be not terrifying, it's the sky above our heads and the ground beneath our feet. Unfortunately, there are plenty of things to be scared of there, too. Not only does a weird amount of freaky stuff tend to fall from the sky, but it's entirely possible the ground could open up and swallow you. It could literally happen any minute now. Not kidding.

What causes them?

Sinkholes are terrifying, but the process that creates them is simple. They happen when groundwater wears away at rock enough to cause a collapse. That's all it takes. Feeling nervous yet?

Most sinkholes happen in areas built on limestone, salt beds, carbonate rock, or any other easily eroded type of rock. Sounds specific, but according to the U.S. Geological Survey, that includes huge sections of Florida, Missouri, Texas, Arizona, Oklahoma, and New Mexico, along with scattered sections of pretty much every U.S. state. When they happen, they can be one or hundreds of feet deep. They can be a few feet in diameter or hundreds of acres.

There are a few types of sinkholes; the one you're probably thinking of is called a cover-collapse sinkhole and is usually pretty catastrophic. There are also dissolution sinkholes, which form gradual depressions that usually turn into ponds, and cover-subsidence sinkholes, which form caves beneath surface depressions. This isn't all doom and gloom; EarthTech says there are some warning signs. Some are weird — doors and windows not closing right, creepy-crawlies suddenly showing up in your house, new cracks in floors or walls, inexplicably wilted foliage, and dead patches of grass. There's also "rapid appearance of a hole in the ground," but seriously, you should already be on your way out of town at that point.

Humans can cause them, too

If there's one thing you have to give the human race, it's the ability to make a big problem even worse. In August 2012, the 350 residents of Bayou Corne, Louisiana, were evacuated when a sinkhole started swallowing their town and everything around it. The entire event was catastrophic, according to Mother Jones. A year later, it covered 24 acres and was around 750 feet deep. Its location means that crude oil and explosive gases were also released, bubbling up through the bayou. Needless to say, no one's moving home anytime soon.

There was a ton of finger-pointing, but most of the fingers were pointed at Texas Brine. The company was drilling in a mine called Oxy3, and Oxy3 was what collapsed. While it has admitted at least partial fault, plenty of other companies are drilling and hollowing out these massive caverns. They're all over, usually used for storing things like toxic waste and petroleum, and they sometimes cause sinkholes. In 1980, another sinkhole opened up in Louisiana's Lake Peigneur. That one happened when Texaco punched through the walls of a salt mine drilled beneath a lake, and the sinkhole's vortex was so massive it sucked in 11 barges. Mother Jones talked to a resident who saw the whole thing unfold; she said it looked like "a little ducky in a bathtub going down the drain."

Sinkholes are swallowing the Dead Sea

The Dead Sea is dying. Haaretz says the Dead Sea was 398 meters below sea level in 1976, and by 2016, it had dropped to 428 meters below sea level. It dropped 11 meters in a single decade, more than any prior decade. There's another problem, too — the sinkholes. They first started happening in the 1980s, and by 1996, there were 220 of them that had popped up along the shoreline. In 2006, there were 1,808. In 2016, there were 5,548, and it doesn't take a math genius to figure out that's a heck of a lot of sinkholes in just a few years.

No one's 100 percent sure what's going on, but it may have something to do with the disappearance of the Dead Sea's saltwater, possibly being replaced with fresh water underground and wearing away underground caves to create the sinkholes. We also know sinkholes are happening in creepily straight lines and are keeping floodwaters from reaching the sea. The more sinkholes there are, the more water is being channeled underground, the more salt is being dissolved, and the more new sinkholes are created — at a rate of at least one a day. Beaches have already been abandoned, and geologists are scratching their heads for a solution. One idea involves opening a "Sinkhole Park" tourist attraction, because of course it does.

Saturn's moon has sinkholes filled with liquid gas

When the Cassini spacecraft found lakes on one of Saturn's moons, it seems like the stuff ancient astronaut theorists should love. Titan's surface is a chilly -292 Fahrenheit, though, and according to NASA's Jet Propulsion Laboratory, the lakes and seas aren't filled with water at all. Instead, it's liquid methane and ethane, and even stranger, the lakes seemed to drain and fill without any rivers or precipitation to fill them. Since Titan's seasonal cycle is longer than Earth's, the mechanics of the lakes were a little hazy ... until 2015, when JPL revealed the lakes weren't so much lakes but sinkholes of the very same kind we have on Earth. Studies done by the European Space Agency took into account things like the makeup of Titan's surface, the weird weather patterns, and the properties of liquid hydrocarbons, and ultimately found the same weathering processes and sinkhole formations happening right here on Earth are also happening a billion kilometers away. It's a small universe after all.

The world's deepest sinkhole has an ecosystem

There are tons of sinkholes dotting China's landscape, thanks to its high proportion of karst rock and the underground rivers that formed in the southwest. One of the deepest is Xiaozhai Tiankeng, and it's nearly 2,000 feet from the surface to the river at the bottom. It was only discovered in 1994 — well, "discovered" by people who didn't live there. Locals have known about it forever, and it's named after a now-abandoned village nearby. According to The Earth Story, the sinkhole was formed about 10,000 years ago, and even though the river at the bottom is around 5 miles long, that's the only place you can actually see it.

It's tough to imagine just how deep it is, so here's a fun fact: the Empire State Building has 103 floors and is around 1,500 feet tall. If you don't include the antenna, you could almost fit two of them inside the Xiaozhai Tiankeng sinkhole, one on top of the other.

That's huge, and it's almost as wide as it is deep. It's so huge it has its own ecosystem, and scientists have identified more than 1,285 plants and animals living in the sinkhole. There are even some clouded leopards that have been spotted prowling about in the trees at the bottom. Someone needs to explain how they got there.

What happened to those Corvettes?

On February 12, 2014, car enthusiasts across the globe suffered a case of collective heartbreak when a sinkhole opened beneath the National Corvette Museum in Bowling Green, Kentucky. Eight cars were swallowed. By August 2015, The Guardian reported the worst of the damage had been fixed ... to the building, at least. The cars were another story. Even when they were rescued from the bottom of the pit, it wasn't pretty. The crushed pieces of metal that were salvaged even went on display for a while. Five were well beyond repair, one was restored within a year, and two others were deemed worth restoring.

The 30-foot-deep sinkhole was 60 feet wide and 45 feet long, and Atlas Obscura says the cars the earth ate included a 1992 White 1 Millionth Corvette worth about $750,000 and a 1993 ZR-1 Spyder prototype worth around $250,000. It's never been said just how much the cars were worth in total, but repairing the damage to the building alone cost a whopping $5 million. On the plus side, the museum was able sell thousands of jars of sinkhole dirt and they made an entire exhibit dedicated to the sinkhole, so hey, it wasn't a complete loss. It definitely put them on the map.

They happen underwater, too

Sure, sinkholes are terrifying, but how about sinkholes that happen underwater? In July 2016, Chinese researchers from the Sansha Ship Course Research Institute for Coral Protection (via the Independent) announced the results of their year-long study of the Paracel Islands sinkhole. It's called Dragon Hole, and it's probably the deepest in the world — that we've found so far, at least. Researchers think it's 987 feet deep, a full 300 feet deeper than the previous record holder in the Bahamas. It's also got an epic place in Chinese lore: local fisherman say it's the place the Monkey King got his golden cudgel.

Researchers obviously couldn't dive that deep to explore, but they used an underwater robot to probe the hole and discover 20 new species of fish living in the upper 300 feet. Beyond that, there's no oxygen — and no life — which makes for some seriously surreal footage. The government officially issued protection orders with the discovery and renamed it the Sansha Yongle Blue Hole. Dragon Hole is definitely catchier.

The deadliest dive spot in the world is in a sinkhole

Tarek Omar is a rescue diver at the Blue Hole of Dahab, and when Spiegel asked him how many bodies he'd brought to the surface, he simply said, "I stopped counting at some point." The Guardian reported he's recovered the remains of at least 20 people, enough to earn him the nickname "the bone collector," and the cliff along the bay is lined with memorials to those who died there. What makes this place so dangerous?

Locals say it's the dead girl that lurks in the murky waters of the blue hole, unable to rest and looking for revenge on her father, who forced her to drown herself there. According to Omar, he hasn't seen this mythical soul, but he has seen what is so disorienting to divers. About 150 feet deep, past the layers of warm surface water, yellow and orange light, and finally into the blue, the sunlight returns. It's a tunnel, and it opens into the Red Sea. Most people die trying to swim (intentionally or not) through the tunnel. Such deep conditions are disorienting the same way a few drinks are disorienting, and Omar says the other big problem is divers are often completely unprepared for what they're going to face. Even the most experienced, most skilled divers have died there, too — like Irish rescue diver Stephen Keenan. He died rescuing another diver trying to free-dive (i.e., without an oxygen tank) through the arch, and that might be the very definition of insanity.

The Maya believed they led to the underworld

Underwater sinkholes have an unmistakeable air of otherworldliness about them. Regardless of your views on the afterlife, it's easy to see why the ancient Maya believed the next life was at the bottom of a cenote. In 2014, National Geographic reported on an archaeological investigation into a cenote that's still got such a reputation that locals presented offerings to the gods before the divers went in. Sacrifices have been made at cenotes for hundreds of years, with many made in hopes of appeasing the gods and getting their helping during droughts.

Local belief says the cenote has a guardian spirit that will grab anyone disrespectful enough to come near. Might be worth looking into — the team found human remains, including skulls flattened in the traditional Mayan way, on the first dive. This sinkhole isn't a straight shot down, either. Exploring the farthest chambers of the ancient burial ground is defying death, with diver Bradley Russell describing it as "crawling on your belly with your tanks against the ceiling." So much nope.

It's unclear why that particular cenote became the final resting place for these people, but they may have been plague victims buried in a cenote isolated from others. And don't worry — Archaeology magazine says the cenotes used for ritual sacrifices were different sinkholes than the ones used for domestic purposes. No one wants to find a bit of human sacrifice in their drinking water.

Sometimes, sinkholes just happen

Imagine you're spending a day at the beach, just walking along enjoying the sun, the sand, and possibly a travel mug filled with something alcoholic. Suddenly, the ground opens up and swallows you. You're gone, and you'd better hope someone's up there looking for you. Terrifying, right? That's exactly what happened to Nathan Woessner on July 12, 2013 (but without the alcohol, as he was only 6).

He and his family were visiting the Indiana Dunes National Lakeshore when the sinkhole swallowed him. He spent three and a half hours at the bottom of the 11-foot hole, but this has a happy ending. According to the Chicago Tribune, he made a full recovery.

It wasn't as happy an ending for the park, though, which closed while researchers tried to figure out what the heck was going on and why there were suddenly sinkholes eating children. One theory is that trees long buried beneath the dunes are rotting and causing the whole thing to shift, but others think there's more to it than that. Michigan Live reported the beach was going to reopen in 2017, except for a section prone to sinkholes. Sounds like a pretty good reason to stay home and play video games, doesn't it?

Incredible archaeological discoveries have been made in them

It's not just Corvettes you'll find at the bottom of a sinkhole. Archaeological digs done in sinkholes around the world have found some pretty incredible things. In 2013, a team from Kingston University investigating a sinkhole in Hampshire, England, found remains of a Neolithic society. The location — only a few miles from Stonehenge — seemed to yield evidence that Neolithic people had also come across the sinkhole and excavated it for building materials. On the other side of the ocean, sediment samples taken from the Great Blue Hole off the coast of Belize seem to show prolonged periods of drought between 800 and 1000, another clue to the long-standing mystery of what happened to the Mayan civilization (via The Guardian).

The Guardian also reported on an excavation in Florida that seems to change everything we thought we knew about how people spread to North America. The long-standing theory was that a migration took place across the Bering Strait 13,000 years ago, but stone tools and bones found in a sinkhole near Tallahassee push that date back 1,500 years. That's a huge deal, because if our time frame is off, it means the Bering Strait theory is completely wrong. The land bridge was only open for travel for a relatively short time, which might mean it's back to the drawing board on the whole thing.

We can predict them (probably)

So sinkholes are equal parts fascinating and brown-trousers-time scary, but is there anything you can do to make sure your dream house isn't about to be 40 feet underground? Science says, "Maybe."

In 2014, CBS News reported on a new NASA project trying to map sinkholes. Essentially, a plane would transmit electronic pulses and use the data that returned to map shifts in the Earth's crust — one of the precursors of a sinkhole. Since the Dead Sea is already a hotbed of sinkhole activity, Scientific American says it's a great place to perfect technology. That's exactly what researchers from Tel Aviv University are doing, using satellites and aircraft equipped with radar and lasers.

But the BBC says all those efforts aren't without their naysayers ... you know, the people who apparently don't want to know if the ground beneath them might just decide to disappear. In 2013, researchers with the Florida Geological Survey assembled data into a sinkhole vulnerability map, much to the chagrin of property owners in places with a high chance of sinkholes. Those people don't necessarily want to know, especially those looking to sell.