Billings could be buried under up to 1.8 meters of ash if Yellowstone erupted

A present-day eruption of the Yellowstone supervolcano would bury Billings, Montana, under as much as 1.8 meters of volcanic ash, according to a modeling scenario detailed by two disaster researchers and published September 22, 2026. The same model puts Salt Lake City and Boise under tens of centimeters of ash, and describes an eruption column punching 30 to 50 kilometers into the sky. It is a thought experiment about the Yellowstone Caldera as it exists today, not a forecast that the volcano is about to blow.

The scenario comes from Ilan Kelman, a professor of disasters and health at University College London, and Matthew Blackett, a natural-hazards researcher at Coventry University, who built a blow-by-blow account of what a Yellowstone super-eruption would look like under today’s population and climate. Their piece treats the caldera’s last three super-eruptions, a rough 55-to-70-kilometer-wide crater carved out over roughly two million years, as the template for a fourth.

What the ash column would do to nearby states

Kelman and Blackett’s model, first published in The Conversation and reproduced by ScienceDaily, has magma reaching the surface at 650 to 800°C, hot enough, they note, to outstrip the melting points of lead and zinc. The resulting column would rise 30 to 50 kilometers, high enough to inject material into the stratosphere and spread it on prevailing winds. Billings, roughly 150 kilometers northeast of the park, sits closest to the heaviest fallout in their scenario and would take up to 1.8 meters of ash, enough to collapse roofs, choke engines and shut down the city’s water and power systems for an extended stretch. Salt Lake City and Boise, farther from the vent, would still see tens of centimeters piling up, enough to ground aviation and bury crops across the wider region.

It is a genuinely different scale of hazard than the wildfire smoke or winter storms Billings residents already plan around. Ash that heavy does not just dust a windshield; it collapses flat roofs, seizes vehicle engines and turbine intakes, and, once wet, sets like a loose concrete that snaps power lines and buries irrigation systems across the wider Yellowstone River valley.

Census figures put Billings’ population at just over 100,000 people, according to the U.S. Census Bureau’s QuickFacts for the city, which gives a sense of how many residents would face that ash load directly rather than as a downwind nuisance.

Evacuating 200,000 people around Yellowstone National Park

Before any ash falls, the scenario assumes authorities would order an evacuation extending 100 kilometers beyond the park’s boundary, a radius the researchers estimate would displace roughly 200,000 residents plus the seasonal visitors already inside the park. That is a logistics problem on a scale the region has never had to plan for outside tabletop exercises, given how much of the surrounding land in Wyoming, Montana and Idaho is rural and served by a limited highway network.

Kelman and Blackett’s model does not stop at the regional blast zone. They also modeled the climate aftermath: sulfate aerosols lofted into the stratosphere by the column would scatter sunlight and could cool the planet by about 1.5°C, a swing on the order of what volcanic winters have produced after past super-eruptions, with knock-on effects for growing seasons well outside North America.

Why USGS says Yellowstone is not overdue

The scenario is explicitly hypothetical, and the agency that actually watches the caldera is careful to say so. The U.S. Geological Survey’s own FAQ states plainly that “Yellowstone is not overdue for an eruption”, noting that its three past super-eruptions, 2.08 million, 1.3 million and 631,000 years ago, do not fall on any predictable schedule despite averaging roughly 725,000 years apart. USGS also reports that the rhyolite magma reservoir beneath the caldera is only 5 to 15 percent molten, which leaves real uncertainty about whether there is enough mobile magma to drive an eruption at all right now.

That reservoir and the ground above it are watched continuously. The Yellowstone Volcano Observatory runs a network of seismographs and GPS stations across the park specifically to catch the kind of swelling or earthquake swarms that would precede any real eruption, and the agency has reported no such signal. Kelman and Blackett’s exercise is built on that same absence of warning signs; it asks what the numbers look like if an eruption happened, not whether one is imminent.

Between the two past super-eruptions and the roughly 80 smaller, largely non-explosive eruptions USGS has documented at Yellowstone since the last big one, the caldera has stayed active in a low-grade way for hundreds of thousands of years without repeating the 631,000-year-old event. Whether it ever will again, and on what timeline, is a question the agency’s own monitoring network is built to keep asking rather than answer in advance.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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