After the Parking Lot Collapse: What Happens When the Earth Opens its Mouth?

About eight years ago, a horrifying and exceptional incident occurred in Florida, when a man disappeared into a sinkhole that opened beneath his bedroom. The man, a 34-year-old American, was considered missing for many days until the search for his body was eventually called off.

His brother told the rescue forces about the terrifying moments: "Around 11 PM, there was a loud noise, and then I heard my brother shouting for help. By the time I reached his room, there was no bed, no furniture, and all I saw was a big hole and the top part of the bed. I tried to rescue him, but I couldn't, and I kept hearing him scream."

Rescue forces arrived at the scene, but they were unable to establish contact with the missing brother. They estimated that the sinkhole was at least 10 meters deep and that, essentially, the entire house was within the sinkhole.

Why do we now recall the Florida incident? Precisely because of the exceptional event that occurred this week at the Shaare Zedek Hospital parking lot in Jerusalem when part of the open parking lot collapsed due to a sinkhole opening in the ground, damaging several cars that fell in. Hours later, it was speculated that this was due to the collapse of a part of Highway 16, which had been dug there about six months earlier, but there is still no clear explanation for it.

So what are sinkholes, how do they form, and could such a sinkhole appear in your backyard?

The collapse site (Photo: Olivier Fitoussi, Flash 90)

When the Earth Opens its Mouth

We posed the question "How does a sinkhole form?" to Prof. Michael Tsessarsky, a faculty member in the Department of Earth and Environmental Sciences and the Department of Civil and Environmental Engineering at Ben-Gurion University. "It's a complex story," claims Tsessarsky. "By dictionary definition, a sinkhole is essentially a cavity that forms underground until at some point it collapses inward into itself, swallowing everything above it. In other words, part of the sinkhole formation is an unseen phenomenon where a hole develops underground. Today, it is possible to identify this development through monitoring by geologists or satellite tracking, but externally it cannot be seen."

"If we try to describe it in simple terms," he adds, "think of it like a cave underground that at some point can no longer support the cover above it, and then everything collapses inward and is swallowed. Anyone who saw the images of the Shaare Zedek parking lot this week likely noticed exactly this description – under the ground, there's a huge pit that was only revealed when the cover wasn't strong enough, collapsing inward."

How long does it take for a sinkhole to form?

"It varies from one sinkhole to another. It depends on the underground structure and the groundwater present. In general, it's essential to understand that typically several combined processes lead to sinkhole formation. It's not that a single process can be singled out as the cause."

Dead Sea Sinkholes

It's no secret that the most known and dangerous sinkholes in the country are in the Dead Sea region. "There, specifically, the reason for their formation is known," notes Tsessarsky, "they develop due to the dissolution of a thick salt layer formed with the retreat of the Dead Sea in the past. Groundwater dissolves the salt, resulting in the mud clay following the flow into the cavity formed beneath it. Thus, a cavity forms above the mud clay layer. For now, it isn't visible from the outside because above the clay is a dry clay layer whose particles are tightly bound together, thus remaining intact above the cavity beneath it. Over the years, collapse cracks form in this dry layer, which gradually expands until it ultimately collapses into the mud clay beneath it."

(Photo: Shutterstock)

Let me hazard a guess: the cause of the sinkholes in the Dead Sea area is not the same as what led to the sinkhole formation this week at the Shaare Zedek parking lot...

"Regarding Shaare Zedek, it's still too early to know what really happened, especially since there isn't a formal investigation yet. In my opinion, and this is just a personal assumption, it might be related somehow to the dissolution of limestone formed underground. Perhaps the area was initially stable, but since it was dug as part of the roadworks and underwent engineering development, it created the cavity leading to the ground collapse. It's very possible that the work done in the past year was the trigger, but the process itself developed over years prior. Of course, only a formal investigation could confirm such a theory."

Detecting the Sinkholes

Prof. Tsessarsky claims there's a very clear distinction between sinkholes that form due to ground conditions and those where the ground collapses for other reasons. "When discussing sinkholes, many recall an event that happened about twenty years ago in Be'er Sheva, when a hole opened in the ground, and a person fell in and died," he notes, "What not everyone knows is that in that case, it wasn't a natural sinkhole at all, but apparently an ancient water cistern. Such an event isn't related to the geological conditions of the soil and can happen in various locations because it isn't connected to the sinkhole phenomenon. In contrast, when it comes to sinkholes created over cavities, as I described earlier – it's very rare to encounter them in populated areas. It requires a combination of many factors for the cavities to form."

Prof. Tsessarsky

Is there a way to pre-identify high-risk areas?

"Currently, in the Dead Sea area, work by the Geological Institute is underway, through which high-risk areas are identified in advance of potential sinkhole formation, ensuring they're fenced off, and people are kept away. Of course, in built areas, such as within cities, it's more complex to do this. On the other hand, in these territories, sinkholes might potentially pose more danger. Imagine, for instance, that the sinkhole at Shaare Zedek had opened a few meters to the right or left; it could have swallowed parts of the hospital building, possibly leading to its collapse. It's not simple at all."

Are you worried about the occurrence of similar incidents?

"I'm not worried because, in general, the formation of sinkholes is rare. However, it's crucial for professionals involved in construction to be aware of the issue and take precautions. Although buildings today are generally constructed stably and according to all standards, including those designed to maintain buildings during earthquakes, which also partially help protect against sinkholes, buildings constructed before 1980 are not built in such a way, potentially endangering their occupants if the earth, Heaven forbid, opens its mouth."