Scientists estimate a worst-case Yellowstone super-eruption could eventually kill up to 1.3 billion people through famine, disease and collapsed infrastructure, according to a detailed hypothetical timeline published by disaster and volcano experts.
The scenario, published in The Conversation, was developed by researchers who modeled what would happen if the Wyoming supervolcano dormant for roughly 631,000 years were to awaken. It is not a prediction but a scientific thought experiment built on existing research and historical disaster responses.
The first sign would appear almost routine: a swarm of small earthquakes beneath Yellowstone’s caldera, spotted by an analyst at the University of Utah Seismograph Stations. These facilities monitor the area round the clock via seismometers, GPS stations and gas sensors. Initially dismissed as unremarkable, the swarm would migrate upward over the following month with accelerating ground uplift, prompting Yellowstone’s Volcano Alert Level to rise from “normal” to “advisory.”
Within weeks, the probability of a major eruption within three months would jump from 6-9% to 21-27%, triggering quiet evacuation planning from FEMA. Two weeks before eruption, scientists would put the odds of a cataclysmic blast within three weeks at 85-92%, prompting a 100-kilometre evacuation zone around the park affecting roughly 200,000 residents.
When the eruption hits, magma reaching 650-800°C would fragment into ash and pumice, hurling an eruption column 30 to 50 kilometres into the sky. The column would be visible from Denver, some 800 kilometres away. Pyroclastic density currents would flatten and incinerate everything for tens of kilometres, with researchers estimating up to 1,000 immediate deaths from the blast itself.
The immediate casualties would only be the beginning. Within days, Billings, Montana could be buried under up to 1.8 metres of ash, while Salt Lake City and Boise would receive tens of centimetres. Ash contaminating power lines would cause widespread electrocution and fire risks, and collapsing infrastructure would knock out water treatment, sewage and communications across multiple states.
The longer-term toll is where the numbers become staggering. Sulphur dioxide pumped into the stratosphere would trigger a global cooling episode of up to 1.5°C, devastating crops across North America and driving global food prices sharply upward. A decade on, researchers estimate the eruption’s ripple effects could push global freshwater shortages from 4.4 billion to 4.8 billion people, while the world’s population could fall from 8.3 billion to 7.9 billion. Scientists behind the analysis put the eventual excess mortality figure at between 0.7 and 1.3 billion premature deaths, with potentially double that number left with lasting health effects.
The experts stress this remains an extreme, worst-case hypothetical. As they put it, the eruption “did not end humanity, or come close to doing so.”
The Yellowstone supervolcano last erupted on this scale approximately 631,000 years ago, forming the caldera that now sits beneath much of the national park.