Don't Call The Guatemala Sinkhole a Sinkhole

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Click on the photo to see more images of the aftermath of tropical storm Agatha.

The giant sinkhole that opened beneath downtown Guatemala City over the weekend is all the rage right now. There's just one problem: it isn't a sinkhole.

"Sure, it looks a lot like a sinkhole," geologist Sam Bonis told Discovery News from his home in Guatemala. "And a whale looks a lot like a fish, but calling it one would be very misleading."

Instead, Bonis prefers the term "piping feature" — a decidedly less sexy label for the 100-foot deep, 66-foot wide circular chasm. But it's an important distinction, he maintains, because "sinkholes" refer to areas where bedrock is solid but has been eaten away by groundwater, forming a geological Swiss cheese whose contours are nearly impossible to predict.

The situation beneath the country's capital is far different, and more dangerous.

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The lion's share of the city is built on pumice fill — ash flows made up of loose, gravel-like particles deposited during ancient volcanic eruptions. In places, the debris is piled over 600 feet thick, filling up what would otherwise be a v-shaped valley of faulted bedrock. For those peering into the deep dark depths wondering what might be at the bottom, it's either more pumice fill or bedrock. Mixed with a healthy dose of wreckage from the swallowed-up clothing factory.

In 2007, a similar hole opened after a sewage pipe broke pipe just a few blocks from this weekend's disaster. Bonis was part of a team of geologists and engineers brought in to investigate and advise officials on what went wrong.

"Our recommendation was that this could happen again," he recalled. "When you have water flowing from storm water runoff, a sewage pipe, or any kind of strong flow, it eats away at the loose material. We don't know how long it has to go on before it collapses. But once it starts collapsing, God help us."

The Guatemala City metro area is home to nearly 3 million people. Not all of them live on the fill — Bonis estimates around 1-1.5 million, with the rest perched on the valley walls — but by mislabeling the feature a sinkhole, it distracts from a dangerous situation that could be mitigated, if not neutralized, by better handling of the city's runoff and waste water.

"I'd hate to have to be in the government right now," Bonis, who worked for the Guatemalan government's Instituto Geografico Nacional for sixteen years, said. "There is an excellent potential for this to happen again. It could happen almost anywhere in the city."

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