Paha Sapa Grotto

Sinkhole Search Reveals Neighborhood Was Built Over Unstable Gypsum Mine

Updated September 8, 2021

Sometimes things can seem normal and even idyllic, but are actually just barely propped up by a rapidly failing foundation.

This is a phenomenon that's well-known to building and structural inspectors who likely see deceptively pleasant homes with dangerous structural issues on a daily basis. However, it turns out that this happy façade can apply to entire neighborhoods and even larger systems.

While there could very well be many parts of our lives we can identify as seeming ideal despite the unstable foundation holding it up, this became unfortunately obvious for the residents of one South Dakota neighborhood.

And we'd never know why that is if it weren't for some adventurous cavers.

On April 27, a sinkhole suddenly ripped a massive hole in the Hideaway Hills subdivision of Black Hawk, South Dakota.

Facebook | Meade County Emergency Management

As The Rapid City Journal reported, this hole widened to about 50 feet after it broke water and sewer mains in the area.

As a resident named Albert Reitz said, "I felt suction behind me and a little bit of movement under my feet. I looked behind me and I was only a foot away from it."

Unfortunately, this sinkhole and a smaller one that formed across the street has left 12 families stranded and losing money.

Facebook | Meade County Emergency Management

According to the Rapid City Journal, all have been displaced after the area around the sinkhole was evacuated and many of them are spending weeks covering their own hotel expenses without any idea of when or even if they can return to their homes.

Soon after the hole formed, three members of the Paha Sapa Grotto offered their expertise as cavers and explored it.

Facebook | Meade County Emergency Management

As Meade County Emergency Management wrote on Facebook, this was a potentially dangerous job for them because, as they put it, "Think of a mine field where the mines pull you down instead of blowing up. The fall may be a thrill but the sudden stop 30 feet below will not be."

Instead of a natural mine field, however, the cavers found an old gypsum mine that turned out to be at least 600 feet long.

Paha Sapa Grotto

As The Rapid City Journal [reported]((https://rapidcityjournal.com/news/local/12-blackhawk-families-displaced-after-sinkhole-exposes-abandoned-gypsum-mine/article_c48e901e-9ba9-546c-a1ac-c6d66af9e6b8.html), the drilling holes were unmistakable, as was this plank of wood that had been placed here decades ago.

Although the mine could be even longer, the cavers found collapsed areas that were too dangerous to explore.

Although the mine was owned by the Dakota Plaster company and opened as early as 1910, it's unclear when exactly it closed.

Paha Sapa Grotto

As Adam Weaver–one on the cavers–said, building on gypsum is a bad idea at the best of times because it's very water soluble and sinkholes can form when enough ground and surface-level waters eat away at it.

Considering that issue gets even worse when you build over a mine like this, the sinkholes seemed almost inevitable.

And so, the question that seems to remain unanswered concerns whether those involved in planning the subdivision knew what exactly they were building on.

Paha Sapa Grotto

Although The Rapid City Journal were able to find out the developer's name and that they had built the community in 1992, any other information about them seems to be unavailable.

So not only are residents left to wonder whether they'll be compensated for the potential loss of their homes, but also whether both the developers and government overseers failed to examine what they were building on. And if they did know, why they proceeded anyway.

h/t: The Rapid City Journal

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