The Yellowstone Question: Understanding Supervolcanoes
No discussion of volcanoes in the USA is complete without addressing Yellowstone. The term “supervolcano” often conjures images of a global catastrophe, and headlines frequently speculate about an imminent, world-altering eruption. The question `is the Yellowstone supervolcano going to erupt` is a common source of public anxiety, but the scientific reality is far more nuanced and significantly less alarming than often portrayed.
Yellowstone sits atop a massive caldera, a collapsed volcanic crater, formed by its last supereruption approximately 631,000 years ago. A “supereruption” is formally defined as an event that ejects more than 1,000 cubic kilometers (240 cubic miles) of material, registering as a magnitude 8 on the Volcano Explosivity Index (VEI). Such an event would have devastating global consequences, including a “volcanic winter” caused by ash and gas blocking sunlight. However, the probability of such an eruption occurring at Yellowstone is exceptionally low. Scientists at the Yellowstone Volcano Observatory (YVO) state that the annual probability is about one in 730,000, comparable to the risk of a catastrophic asteroid impact.
The YVO, a partnership between the USGS, the University of Utah, and Yellowstone National Park, operates one of the most extensive volcano monitoring networks in the world. This network constantly tracks seismicity, ground deformation, and hydrothermal activity. The data shows that the magma reservoir beneath Yellowstone is mostly solid, not a giant chamber of molten rock ready to erupt. The system is not currently showing any signs that would suggest an impending supereruption.
The far more likely volcanic hazards at Yellowstone are much smaller and more localized. The greatest risk comes from hydrothermal explosions. These are steam-driven blasts that occur when superheated water flashes to steam, fracturing the rock above. These events can hurl large rocks hundreds of feet and create craters, as seen with the Mary Bay crater formation about 13,000 years ago. While dangerous to anyone in the immediate vicinity, they are a localized hazard. Strong earthquakes, a constant feature of the tectonically active region, also pose a significant risk.
The most likely form of a magmatic eruption would not be a supereruption, but a much smaller lava flow. The last such event occurred about 70,000 years ago. While a future lava flow would be highly disruptive within the park, it would not have continental or global effects. In summary, while the Yellowstone system is active and warrants close monitoring, the data indicates that the risk of a catastrophic supereruption in our lifetimes is exceedingly small. The more pressing hazards are those that the park already manages: earthquakes and localized hydrothermal events.
