Every now and then a horrifying news story reaches the airwaves, detailing a gaping chasm that’s appeared seemingly without warning beneath our very feet. These sinkholes can be deadly, growing large enough to swallow entire buildings – but where do they go?

What’s waiting at the bottom of a sinkhole depends on how it was formed, but in the worst cases, they can plunge hundreds of meters into the ground. Erosion is a key driving force, but human activity can increase the risk of them forming.

Human-made “sinkholes”

One incredibly deep sinkhole is the Guatemala City Sinkhole, which swallowed a three-story building during Tropical Storm Agatha back in 2010. The resulting chasm was 20 meters (66 feet) wide and 91 meters (300 feet) deep, but geologist at Dartmouth College Sam Bonis told National Geographic that it should fall under the category of a “piping feature” as true sinkholes are formed by natural processes, not human activity. However, the US Geological Survey states that sinkholes can be human-induced.

This region of Guatemala sits on hundreds of meters of pumice that was laid down during past volcanic eruptions. Combined with weaknesses in the sewer system, this may have led to the formation of an enormous cavity that then collapsed.

A similarly human-made disaster unfolded in 1980 when Lake Peigneur in Louisiana disappeared, swallowing most of an island and reversing a canal. It was the consequence of a drilling disaster that struck a salt mine, resulting in a sinkhole that created a vast whirlpool and drained the lake.

Types of sinkhole

Sinkholes can also appear without humans interfering with the landscape, as a result of natural processes that create depressions or holes in the ground and lead to a collapse of the surface layer. This occurs in three main ways:

Dissolution sinkhole: Chemical weathering can erode soluble bedrock like chalk, gypsum, or limestone, as acidic rainfall saturates land and drains away. This creates depressions or cavities as the rock dissolves, creating sinkholes that form gradually.

Cover-Subsidence Sinkholes: These sinkholes form like gradually deepening depressions as the loose surface layer of sediment trickles down into gaps in the underlying rock below.

Cover-Collapse Sinkholes: The most dangerous sinkholes form when a void starts to form underground, often due to erosion from a water source (natural or human-made). Eventually, the roof of the void can no longer be supported, and it suddenly collapses. These can be deadly.

Where do sinkholes go?

In the instance of a cover-collapse sinkhole, any physical objects that fall inside will plummet into the cavern that caused the sinkhole in the first place. That cavern can be anything from a couple to hundreds of meters, and large objects may have to be left to decay at the bottom if a rescue mission is too dangerous or expensive.

Any liquids that fall in may be carried away to the nearest spring, as demonstrated by a sinkhole in Florida that sat above the aquifer that feeds Wakulla Springs. The region is particularly vulnerable to cover-collapse sinkholes because of a network of underground caves in the limestone bedrock that’s been carved out by millions of years’ worth of rain.

Can we predict when a sinkhole is about to appear?

The voids that result in cover-collapse sinkholes can develop slowly and do so underground, making it hard for geologists to predict when and where sinkholes are likely to appear. In the cases of human-driven sinkholes, we can be aware of the processes or faulty sewer systems that may increase the chance of sinkhole formation, but vast areas of land can be predisposed simply due to the nature of the bedrock they sit on.

The good news is that NASA has reported on radar technologies that may make it easier to spot where huge sinkholes are likely to appear. Analyses of radar data from before a sinkhole formed along the Louisiana Gulf Coast found that the ground surface layer deformed significantly at least one month before collapse.

“While horizontal surface deformations had not previously been considered a signature of sinkholes, the new study shows they can precede sinkhole formation well in advance,” said Cathleen Jones of NASA’s Jet Propulsion Laboratory in a release. “This kind of movement may be more common than previously thought, particularly in areas with loose soil near the surface.”

As well as causing the ground to crumble beneath our feet, sinkholes can cause whirlpool formation when they happen underwater. If you’ve ever wondered what happens if you get sucked into one of those, boy do we have the article for you.

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.