There’s a 4-foot-wide sinkhole outside President Trump’s private Mar-a-Lago club in Florida, apparently caused by a recently installed water main, according to a Palm Beach traffic alert issue Monday.
The news prompted an inevitable flurry of wisecracks, from Vox’s own Matt Yglesias among others.
Trump starts fucking with mystical orbs and the next day a sinkhole opens in front of Mar-a-Lago. He has no idea what he's unleashed.— Matthew Yglesias (@mattyglesias) May 22, 2017
But sinkholes aren’t all that funny when they happen in your backyard. The US Geological Service estimates that sinkhole damages average at least $300 million a year. And Florida leads the nation in sinkhole damage, reporting some of the most shocking incidents in recent years.
There was the sinkhole in 2013 near Tampa that swallowed an entire bedroom in a house, killing one of the residents. And later that same year there was a 60-foot-wide sinkhole outside Walt Disney World amusement park in Orlando that destroyed a resort (luckily none of the guests were injured).
We’re still really bad at predicting when sinkholes might occur, as there are few warning signs. As a result, sinkholes can often be catastrophic.
What’s more, we could be seeing more sinkholes as our population grows and climate change triggers more extreme events like tropical storms and flooding (although the science here is tenuous and more research is needed).
Sinkholes happen when water erodes the soil, making deep, unstable holes under ground
A sinkhole is formed when water pools underground because it doesn’t have a way to drain naturally and instead slowly erodes the underlying rock. Over time, this process weakens the subterranean structure and creates a cavernous hole that eventually causes the ground to collapse.
Generally speaking, sinkholes are most prevalent where the bedrock is made up of rock like limestone, dolomite, and gypsum that dissolve over time from water — particularly acidic water, or most rainwater in the US. This type of soil structure is referred to as “karst” and can be thought of as a block of Swiss cheese — with holes beneath the earth’s surface formed by groundwater eroding the rock.
Below is a map of regions in the US where this type of soil structure is most common. The USGS estimates that anywhere from 35 to 40 percent of soil in the US is composed of karst.
And as you can see, large swaths of Florida are at risk of sinkholes:
In Florida, nearly all sinkholes are the result of rocks beneath the surface gradually dissolving from rainfall and groundwater.
There are two other sinkhole types. One is known as “cover subsidence” and is most common in sandier soils. The process of soil leaching into a hole below ground is usually very slow — taking years or even hundreds of thousands of years — and is most common in areas like the Shenandoah Valley where there are many naturally occurring caves.
And then there are “cover-collapse” sinkholes, which can happen in a matter of hours and are far more dramatic and headline-grabbing. They usually occur in areas with large amounts of clay in the soil; as soil is deposited into a hole below, an arched cavity is created just beneath the surface that moves upward as more soil is eroded.
According to the Florida Office of Insurance Regulation, reported claims from sinkhole damages nearly tripled over four years, from 2,300 in 2006 to 6,700 in 2010, and cost Florida insurers $1.4 billion in damages over this time period. The office also found an increase in reported sinkholes in parts of South Florida where they traditionally had not been an issue.
(State insurance officials told Weather.com there’s no geological explanation driving this spike and it’s instead a reflection of better reporting practices and, in some instances, dubious claims.)
Climate change might make sinkholes happen more frequently, but remote sensing could let us detect them sooner
Sinkholes occur naturally, but can also be triggered by extreme weather events like flooding and tropical storms, and other kinds of human activity. (It’s thought that the installation of a new water main on South Boulevard triggered the sinkhole in front of Mar-a-Lago.)
Now some scientists are trying to better understand the relationship between sinkholes and climate change. It’s a relatively new question in climate science, and at this stage, researchers haven’t definitively established a relationship. But Harley Means, a geologist at the Florida Geological Survey (FGS), told New Scientist in 2013 that studies that examined periods of high sinkhole activity with corresponding climatic conditions could potentially provide evidence of a cause-and-effect relationship.
The USGS doesn’t currently collect national data on sinkholes, which makes it incredibly difficult for scientists to determine if sinkholes are increasing in frequency or severity — let alone what is driving these changes.
But there is hope that a new remote sensing technology that NASA developed might make detecting sinkholes earlier. It's called interferometric synthetic aperture radar (InSAR), and it works through having satellites and drones capture changes in ground elevation. The thought is that because sinkholes often show signs of gradually caving downward (though not always), InSAR can be used to detect when a sinkhole has reached a critical point and collapse is imminent.
Ronald Blom, a geologist with the Jet Propulsion Laboratory, cautioned the Atlantic that “InSAR is not a magic bullet” and won’t capture every sinkhole, but it could be useful for detecting sinkholes earlier.