Yellowstone supervolcano is only lukewarm

By Catherine Brahic (Image: US National Parks Service) How hot is the Yellowstone hotspot? At 80 kilometres beneath the Earth’s surface it’s about 1450 °C, say researchers – which, for a supervolcano, is only lukewarm. That doesn’t mean we won’t get another eruption. The last explosion, some 642,000 years ago, created the Yellowstone caldera and blanketed half of the present day US in ash. But Derek Schutt of Colorado State University believes the relatively tepid temperature means the supervolcano could be on its last legs. Yellowstone National Park in the US is one of a few dozen volcanic hotspots around the world, along with the likes of Hawaii and Iceland. What causes it to periodically erupt is not clear. Some researchers think it is disturbances in the top 200 kilometres of the Earth’s interior, but increasingly the evidence is pointing to a large plume of hot mantle rising up from much deeper, melting its way through the crust. Schutt has just added to that evidence. He and his colleague Ken Dueker of the University of Wyoming have estimated the temperature of the plume beneath the Snake River Plain, south-west of the Yellowstone caldera, using the knowledge that temperature affects how seismic waves travel through rocks. “80 km beneath the Snake River Plain, seismic waves travel slower than just about anywhere on Earth at this depth,” says Schutt. The team determined that the temperature at this depth was likely to be between 50 °C and 200 °C hotter than the surrounding rock – at least 1450 °C. According to Schutt, there is no way to reach these temperatures without a plume of magma rising up from deep inside the Earth. Yet, “this is much colder than other presumed mantle plumes, such as Hawaii,” he says. This adds to suggestions that the plume has disconnected from its heat source in the Earth’s core. If this is true, it means the plume could be dying – and that the sequence of mega-eruptions could come to an end. “If it doesn’t have clear source, as it rises eventually the plume will die out,” says Schutt. That doesn’t mean there won’t be another eruption, however, says Jacob Lowenstern of the US Geological Survey’s Yellowstone Volcano Observatory. “Regardless of the ultimate origin of the plume, the volcanic hazard remains about the same,” he told New Scientist. Rhodri Davies of Imperial College London agrees. If Schutt and Dueker’s temperature estimates are correct, he says, there is still enough heat there to trigger eruptions. “I would suspect there is life in the Yellowstone hotspot. To me, ruling out a future catastrophic eruption would be foolish,” he says. Journal references: Geology (DOI: 10.1130/G24809A.1) Journal of Geophysical Research (DOI:
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