Larderello was a fraud.

Diving into the literature, Krippner found records of phreatic explosions, created when trapped water is suddenly warmed by an underlying heat source. These blasts did carve out some craters, but explosions alone also don’t make a volcano. To earn that accolade, magma needed to have breached the surface. But when Krippner looked through older reports about the geothermal wells in the area, she didn’t find any evidence of volcanic deposits.

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Krippner took her suspicions to Ed Venzke, the program’s database manager and a sort of superintendent for the world’s volcanoes. He investigated and also found Larderello wanting. A volcano might have formed if an injection of magma made it higher up in the crust, but this geothermal hot spot just wasn’t meant to be more than that. “It tried really hard to be a volcano,” Krippner says.

It might sound improbable that an impostor ended up sneaking into the volcanological equivalent of the Library of Alexandria, particularly when, on an intuitive level, the characteristics of a volcano can seem pretty obvious. (Was there a fountain of lava here at some point? Et voilà—it’s a volcano.) Definitions weren’t always so strict, though.

Venzke explains that the GVP’s database was jump-started by a series of massive preexisting volcano compilations. Several were put together by the International Association of Volcanology and Chemistry of the Earth’s Interior, or IAVCEI, from the 1950s to the 1970s. Another compilation used extensively by the GVP was published back in 1917. These lists didn’t just include genuine volcanoes; several instances of geothermal fields and other magmatically powered but noneruptive entities made the cut, too.

As those older compilations had rather broad definitions of what constituted a “volcano,” plenty of sites we now know aren’t volcanoes made it onto the lists. That included Larderello, whose craters and steamy earth were enough to let it sneak into those catalogs and, ultimately, onto the GVP’s database.

Its surroundings may have lent a helping hand, says Boris Behncke, a volcanologist at Italy’s National Institute of Geophysics and Volcanology. Aside from the area’s geothermal activity, a couple of bona fide youthful volcanoes sit just down the road and may have provided Larderello with some accidental legitimacy.

Larderello isn’t the only fraud that’s been spotted by the GVP. In fact, Venzke recalls deleting another impostor just this January. Viedma, a suspected Antarctic volcanic area covered by ice, is instead something akin to a mudflow.

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Venzke also mentions what he calls a particularly egregious example: the Pretoria Saltpan crater in South Africa. Back in 2014, he saw it listed on the database as being volcanic in origin, but he knew that the regional geology made that impossible. The crater was thought to be volcanic since the mid-1800s, but by the 1990s scientists had definitively concluded that it was a 220,000-year-old impact crater. As this revelation wasn’t published in a volcano-oriented scientific journal, volcanologists hadn’t seemed to notice the change in its origin story, and the crater had lingered in the GVP’s catalog.