Two disaster researchers have laid out, step by step, what a worst-case Yellowstone supereruption might look like for Denver and beyond, describing a hypothetical evacuation of roughly 200,000 residents, ash plumes rising dozens of kilometers into the sky, and a scenario in which Denver ends up under an average of nearly four inches of ash. It is not a forecast. It is a thought experiment, and the scientists behind it, along with federal geologists, are careful to say the supervolcano beneath Yellowstone National Park shows no signs of waking up anytime soon.
The scenario comes from professors Ilan Kelman and Matthew Blackett, published Tuesday in Westword, which framed the exercise as an analytical model rather than an active hazard alert, according to The Conversation. Kelman, a professor of disasters and health at the UCL Institute for Risk and Disaster Reduction and professor II at the University of Agder in Norway, and Blackett walked through a fictional timeline: an earthquake swarm, a caldera uplift exceeding 15 centimeters per year during 2013 and 2014, a magnitude 4.8 quake, and eventually a Yellowstone Volcano Observatory alert level climbing from normal to advisory and then to watch as eruption probability estimates in their model jumped from single digits to as high as 85 to 92 percent within three weeks. In their hypothetical, the Federal Emergency Management Agency plans a large-scale evacuation and the U.S. Geological Survey raises the aviation color code to orange.
A Hypothetical Eruption Column Tens of Kilometers High
In the scenario, the eruption column reaches 30 to 50 kilometers into the atmosphere; the scenario describes magma temperatures of 650 to 800 degrees Celsius. Westword's account describes a Volcanic Explosivity Index rating of 8 in this modeled event, with the fictional evacuation zone extending 100 kilometers beyond Yellowstone National Park and affecting roughly 200,000 residents, alongside up to 1,000 immediate human deaths in the scenario.
In the hypothetical ashfall pattern described by the researchers, Denver along with the Canadian border would fall within the ash zone, with farmland across at least eight states devastated. That regional picture lines up with a separate 2014 computer simulation using the Ash3D transport model, in which U.S. Geological Survey researchers estimated a supereruption dispersing 330 cubic kilometers of ash would leave an average of 98 millimeters, or about 3.8 inches, on Denver, according to World Atlas. The same modeling put Billings, Montana closer to the source at 1,430 millimeters, or 4.7 feet, of ash, with estimates of 248 millimeters for Salt Lake City and 145 millimeters for Boise. In the professors' scenario, Billings could see up to three feet of ash.
Why Even a Few Inches of Ash Is a Serious Problem
The stakes of an ashfall like that are not trivial. Geological impact assessments show agricultural crop yields and livestock grazing become severely impaired once ash depth reaches 100 to 150 millimeters, with total plant burial at greater depths, per World Atlas — putting Denver's modeled 98 millimeters right at the edge of that threshold. Infrastructure is vulnerable too: technical studies cited by INMR show that as little as 5 millimeters of wet volcanic ash can conduct electricity and trigger short-circuit flashovers on high-voltage power lines and substation transformers, meaning even a modest ash layer could threaten a regional power grid.
The professors' scenario extends the consequences well past Colorado. Volcanic aerosols could influence global climate for several years, though a volcanic cooling episode is unlikely to push the global average down by more than about 1.5 degrees Celsius, per the researchers' modeling described in Westword's report. Their hypothetical decade-after outlook describes a shift to an agrarian lifestyle. The scenario estimates 0.7 to 1.3 billion premature deaths overall — a staggering hypothetical toll, though the researchers are explicit that even this scenario would not end humanity.
What the Actual Science Says About Yellowstone Right Now
None of this describes what is currently happening at Yellowstone. Geophysical imaging indicates the combined Yellowstone magmatic system is estimated at less than 10% melt, according to World Atlas. The U.S. Geological Survey's own probability estimate for a caldera-forming supereruption in any given year is about 1 in 730,000, or roughly 0.00014 percent, as reported by Discover Magazine.
History backs up that caution. USGS records show Yellowstone's three caldera-forming supereruptions occurred roughly 2.1 million years ago, 1.3 million years ago, and 640,000 years ago in northwestern Wyoming, an eruption that dispersed ash across much of North America and affected worldwide climate. But since that last major event, Yellowstone has produced numerous lava flows, most recently the Pitchstone Plateau rhyolite flow roughly 70,000 years ago — meaning gentler lava flows, not supereruptions, are the volcano's normal behavior. USGS scientists also reject the popular notion that Yellowstone is “overdue,” stating that calculating a future eruption date from the intervals between past eruptions is mathematically invalid, per Discover Magazine.
Yellowstone's caldera spans roughly 55 to 70 kilometers across and produces thousands of earthquakes every year, but an earthquake swarm on its own does not indicate the volcano is preparing to erupt, according to Westword's reporting. The 2013-2014 unrest that inspired part of the researchers' fictional timeline was tied to hydrothermal fluid movements rather than magma, the same account notes. Real-world monitoring today includes the University of Utah Seismograph Stations tracking earthquakes beneath the park, alongside the Yellowstone Volcano Observatory's broader watch over volcanic activity. That observatory uses a monitoring network and satellite observations to track volcanic activity, according to the U.S. Geological Survey.
