Written by Kevin Jennings
Sinkholes are a naturally occurring phenomenon normally resulting from underground erosion, at least they used to be. Thanks to drilling and mining operations as well as underground pipes, the majority of sinkholes these days are manmade. A burst pipe or haphazard drilling plans can result in the creation of a sinkhole.
Their sizes can range from just a few feet to over 600 meters (2,000 feet), both in diameter and depth. They can occur anywhere in the world, and they tend to form slowly. In fact, they form so slowly that without incredibly thorough geological research, no one is likely to notice that anything is even happening.
The process takes place beneath the Earth’s surface, completely out of sight. As the ground either erodes or becomes waterlogged, weakening it, it eventually reaches a point where it can no longer support the weight on top of it. Though the process that causes sinkholes is slow, once the breaking point is reached it is not. The ground suddenly and without warning collapses in on itself, leaving a crater that may continue to grow.
Though some places are at higher risk than others, sinkholes are generally common. In Florida alone, the most sinkhole prone state in the United States, there are on average 6,500 insurance claims each year related to sinkholes. Fortunately, most of these sinkholes are small. They rarely result in death or injury, even if they may damage or destroy property. But when a sinkhole forms that is more than just a few feet wide, it can have absolutely devastating consequences.
Agrico Gypsum Stack
IMC-Agrico Company was a fertilizer producer in central Florida. One of the byproducts of fertilizer manufacturing is phosphogypsum. Unlike regular gypsum used in things like plaster, phosphogypsum is toxic, containing heavy metals and radioactive material. However, because it has very low levels of radiation, the industry standard was to simply build piles of it to store indefinitely.
In 1975, Agrico began building such a mountain of gypsum. The waste product was transported in liquid form via pipes to the pile of waste that grew and grew where it would eventually harder. By 1993, when the mountain had reached a height of 200 feet, it was decided that it was tall enough and it was time to start a second mountain. What they did not realize was that the years of liquid runoff into the ground was dissolving the limestone foundation beneath the ground’s clay surface. On top of that weakening ground sat a pile of 100 million tons of toxic waste.
On June 27, 1994, workers were conducting a routine inspection, when they saw a ledge that had not appeared to be there before. They thought better of going any closer and contacted their supervisors, who surveyed the scene via helicopter. What they saw was a massive sinkhole that had swallowed the pile of gypsum. The sinkhole was 160 feet wide and 400 feet deep (49 meters wide and 122 meters deep). Because this was central Florida, locals jokingly referred to the sinkhole as the “Journey to the Center of the World” as though it was a new Disney Word attraction.
Given the location of the sinkhole was a mountain of waste where people wouldn’t be hanging out, it would stand to reason that no one was injured by the sinkhole. Unfortunately, the waste contamination reached the massive underground body of water that supplies 90% of the drinking water in the state of Florida.
Agrico claimed that they could pump water out of the well fast enough to prevent any major contamination, and the water plant stated that the water, though contaminated, remained in compliance with the safety standards for drinking water. It’s hard to know for sure if anyone was injured as a result of this water as the contaminants were predominantly carcinogens that would not have an immediate effect, but either way Agrico was quick to try to rectify the situation.
The company utilized special drills to drill at an angle into the bottom of the sinkhole where they filled the hole with concrete. By April of 1995, ten months after the sinkhole collapsed, they had pumped nearly 3,800 cubic yards of concrete into the hole at a cost of $6.8 million. This did the trick, and the contamination levels in the water supply returned to normal levels.
May of 2010 was a rough time to be living in Guatemala City. On May 27 at 8 pm, the Pacaya Volcano erupted. The eruption only resulted in one death, a news reporter who was one of the first on the scene to cover the story, but there were thousands evacuated and the airport was shut down due to volcanic ash raining from the skies.
This would be enough of a disaster on its own, but at the time the volcano erupted, Tropical Storm Agatha was set to make landfall on the 29th. When Agatha hit Guatemala City, she brought heavy rainfall to Pacaya resulting in lahars, violent mudslides of pyroclastic materials that destroyed everything in their path. By the afternoon of the 30th, there were 15 dead and another 22 missing despite well over 100,000 people already having evacuated the city.
That’s when the sinkhole opened up. Between the volcanic eruption and resulting tectonic disturbances, the tropical storm, and leaking sewer pipes, a 65 foot wide and 300 foot deep (20 meters wide and 90 meters deep) sinkhole collapsed. The sinkhole was directly under a three story factory, which was swallowed whole. The collapse killed at least 15 people and put hundreds more in danger.
The only silver lining for a sinkhole plunging an entire factory ten stories underground is that it was the third in the series of natural disasters, and the least predictable. Since it was early afternoon, the factory would most likely have been full were it not for the volcanic eruption and tropical storm. Were that the case, the death toll of the sinkhole would almost certainly have exceeded the deaths that resulted from all three disasters combined.
What is now the Russian city of Berezniki was first settled in the 16th-17th century, and it was founded as the town of Berezniki in 1873. The city was built directly on top of a massive potash mine, which was standard practice in Russia at the time. Potash is an alkaline potassium compound primarily used as fertilizer, and Berezniki is responsible for roughly 10% of all the world’s potash. There are also huge potassium and magnesium mines beneath the city.
As the mines were excavated over the decades, a large empty void was forming beneath the city. Realizing that this could be structurally unsafe, they had the good sense to build walls and support pillars to keep the ground from collapsing. However, they made the odd decision to build these structures out of salt. This was likely Soviet-era cost cutting, but it is a decision that the city has come to regret.
In 1986, the first sinkhole collapsed. For a long time, nobody really thought anything of it. After all, sinkholes occur all the time all over the world. Then, in 2006, a freshwater spring deep beneath the Earth’s surface began flooding into the mine. A flooding mine is obviously never a good thing, but it becomes far worse when the only things keeping the mine from collapsing are pillars made out of water soluble salt. That’s when the sinkholes really began, and they were numerous.
The largest of the sinkholes opened in 2007, and it is known locally as “The Grandfather”. While most sinkholes tend to be very circular, The Grandfather is much more like a rectangle or oval. When it first opened, it was 130 feet long, 260 feet wide, and over 650 feet deep (80 x 40 x 200 meters). Every year, the sinkhole kept expanding and it is now truly massive. It is now almost five times longer and eight times wider, slowly growing into a more circular shape. The good news, if we can even call it that, is that despite its massive outward expansion, it has only gotten about 25% deeper.
But that’s hardly good news compared to the devastating effects of this sinkhole. What was once just a really big hole is now larger than eight football fields placed side by side. It has destroyed much of the city, and threatens to destroy the only rail line that leads to and from the potash mines.
Shockingly, no one was injured when these sinkholes first opened, but the devastation to the city of Berezniki is undeniable. There are talks to simply relocate the entire city as the sinkhole problem is only getting worse, and it’s made life both scary and depressing for the citizens that have yet to evacuate. After all, what’s the point in bothering to clean your house when the entire thing could just be swallowed whole by the Earth at any moment?
Xiaozhai Heavenly Pit
Not all sinkholes are dangerous, at least as long as you watch where you’re going. Sometimes, they can be a fun tourist destination. To be fair, this sinkhole would absolutely have been dangerous when it first formed, but that was thousands of years ago so with no records going back that far, we’ll just assume everyone was fine.
The sinkhole is in the Fengjie County of Chongqing Municipality in China. It is named Xiaozhai Tiankeng, and it is the world’s largest sinkhole by a sizeable margin. Tiankeng literally means “Heavenly Pit”, and Xiaozhai, which means “little village”, is the name of an abandoned village nearby.
The Xiaozhai Tiankeng is over 2,054 feet long, 1,762 feet wide, and an astonishing 2,172 feet deep (626 x 537 x 662 meters). It is likely the result of a powerful underground river. Locals have known about the sinkhole since ancient times, and a 2,800 step staircase was constructed so tourists can venture deep into the sinkhole. While many modern sinkholes are often pits of dirt, mud, and collapsed buildings, the Xiaozhai Tiankeng is different.
Because it was formed so long ago and is so massive, there has been time for an entire ecosystem to be created within the steep walls of the sinkhole. There are almost 1,300 different species of plants inside the sinkhole, and many rare animals can be found there on occasion as well, such as the clouded leopard or the Chinese giant salamander.
On the night of October 17, 2010, the entire Amazonian port of Chibatao in Manaus, Brazil disappeared. The official response was that a massive wave crashed into the port and pulled everything out to sea, and a ship’s captain confirmed seeing what he thought was a tsunami. We actually know very little about this event, despite much of what happened being caught on video, but we know it was not caused by a wave.
A local happened to have a camcorder handy once the sinkhole began to swallow up the port. In a matter of minutes, a 300 foot (91 meter) sinkhole collapsed beneath the port, pulling cranes, storage containers, shipping trucks, and everything else directly into the water. The wave that was reported came after, likely the result of all of this material crashing into the river.
Unfortunately, six workers were also swept away during the sinkhole’s collapse and their bodies have never been found. To this day we have no idea what caused this sinkhole. Beyond the loss of life, the city of Manaus also lost the port responsible for 40% of all cargo shipments to and from the city.
Atlantis of the Sands
Sinkholes can be so dangerous that they can make an entire city disappear. That’s what happened roughly 1,700 years ago when the city of Ubar on the Arabian Peninsula disappeared without a trace. It was later named the Atlantis of the Sands, both because it disappeared into the sand rather than disappearing into the sea, and because there was no consensus on whether or not the city ever existed in the first place.
Many searches were conducted, and a series of investigations beginning in 1930 finally led to the location of a crumbling fortress in Shisr, Oman. Beneath it was a massive fortress that had collapsed into a sinkhole. Researchers were able to date the octagonal fortress back 2,000 years. The location was named Ubar, though it is still a matter of debate whether or not this was actually the fabled city.
Whether it is or not, the story of this long forgotten city remain the same. It was a massive and prosperous city built on top of a cavern through which water flowed freely. Some amount of moisture is important for the structural stability of the ground, so once the water receded the weight of the city facilitated the opening of a sinkhole. In an instant, the entire city was destroyed as it was swallowed up by the sand. There’s no way to estimate how many people died as a direct result of the sinkhole, but given the size of the fortress it’s probably fair to say a lot.
Of course, there is still the debate over whether or not this was the real Ubar of legend, which does leave us with an interesting question. If this was not the location of Ubar, exactly how many cities are there that were swallowed whole by sinkholes and still remain buried deep in the desert?