Larderello masqueraded as a volcano for many years.VINCENZO PINTO / Getty Images

Janine Krippner was the first to notice something amiss with the volcano.

A volcanologist at the Smithsonian Institution’s Global Volcanism Program, Krippner was doing a routine fact-check in the program’s volcano registry, scrolling through photos of all kinds of volcanoes—from sleeping geological giants to actively raging mountains—while checking the accuracy of their captions. When she stumbled across the page for Larderello, a volcano in Italy’s picturesque Tuscany region, she was naturally expecting to see a volcano. Instead, she was presented with a bizarre shot of several industrial cooling towers associated with a geothermal power plant.

The Smithsonian’s online registry catalogs thousands of volcanoes that were active at some point in the past 2.5 million years. Larderello was just one unremarkable volcano in a huge crowd; once the site of an eruption, it was now home to a sizable geothermal power plant. It is well-established that the area’s groundwater is heated from below by a 4-million-year-old magmatic intrusion. Geothermal activity alone, however, doesn’t make something a volcano.

Though the site was supposedly active in the past 10,000 years or so, in truth no eruptions had occurred there at any point in history. “There’s just no evidence we can see that this was ever a volcano,” Krippner says.

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.

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.

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.

A handful of other imaginary volcanoes have also made it into the database based on unverified reports of volcanic activity. For example, a suspected submarine eruption was reported off the coast of Baja, California, in 1953, when fishing boats saw huge quantities of dead fish and mud appear at the surface of a bubbling sea. It isn’t clear what caused this event, but scientists are now cognizant that no volcano is present in that location.

As part of a recent auditing process, about 50 volcanic charlatans have been removed in the past five years from the list of Holocene volcanoes, those that have erupted at least once during the past 10,000 years. Although spotting impostors was never a common occurrence, Venzke explains that finding any more from this point onward should be relatively rare.

Real volcanoes don’t always have to be frauds to be nixed. Back in 2016, the Pleistocene list, featuring volcanoes active at some point between 10,000 and 2.5 million years ago, was uploaded to the website. The following year, about 45 volcanoes that had been placed onto the Holocene list due to their more contemporary unrest were bumped onto the Pleistocene list, because their activity in the past 10,000 years didn’t include any true eruptions.

Whether volcanoes are full-blown fakes or aging wannabes that have long since flamed out, identifying and purging them is a vital task. “Knowing where volcanoes are and what they produced in the past is key to knowing what they might do in the future or who they might effect,” Krippner says. Finding out that a supposedly active volcano is actually extinct—or, in Larderello’s case, nonexistent—helps volcanologists better prioritize their resources.

Krippner, for one, certainly seems to relish finding volcanic frauds. Larderello was her first confirmed kill, and a few days after it was axed, she contacted me to gleefully report that she had “killed another one”—this time in Eritrea.

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