The Yellowstone Caldera is one of the world’s largest and most active volcanic systems, often referred to as a supervolcano due to its history of massive eruptions. This system is fueled by a plume of hot rock, known as a hotspot, which provides the heat for the park’s famous geysers and hot springs. Despite its power, there is no scientific basis for predicting an imminent catastrophic eruption. The Yellowstone Volcano Observatory (YVO) continuously monitors the area and finds no indication that a major event is likely soon.
Yellowstone’s Major Eruption History
The Yellowstone region has experienced three colossal caldera-forming eruptions over the last 2.1 million years. The oldest was the Huckleberry Ridge eruption, approximately 2.1 million years ago, which produced the largest known output of volcanic material and formed the extensive Island Park Caldera.
Roughly 800,000 years later, the second major event took place, forming the Mesa Falls Tuff and the Henry’s Fork Caldera about 1.3 million years ago. The most recent caldera-forming eruption occurred about 639,000 years ago, resulting in the Lava Creek Tuff and the collapse that created the 45-by-85-kilometer Yellowstone Caldera that defines the park today.
The time intervals between these three events—about 800,000 years and 660,000 years—establish a long recurrence interval for the most destructive eruptions. These explosive events are separated by many smaller, non-explosive eruptions, which are a more common feature. Geologists study these past patterns to understand the long-term behavior of the Yellowstone hotspot.
Current Scientific Assessment of Risk
Scientific consensus holds that the likelihood of a major, caldera-forming eruption occurring in any given year is exceptionally low. By averaging the intervals between the three past major events, the yearly probability of another catastrophic eruption is estimated to be approximately 1 in 730,000, or 0.00014%. This figure is similar to the probability of a large asteroid impact.
The Yellowstone Volcano Observatory currently sees no evidence of an imminent eruption of either a catastrophic or a smaller magnitude. Much more likely than a massive eruption are less explosive events that would pose a far smaller hazard. The most common type of future activity would be a non-explosive rhyolite lava flow, similar to the many flows that have occurred since the last caldera formation.
The last magmatic eruption, a lava flow on the Pitchstone Plateau, took place about 70,000 years ago. Another potential hazard is a hydrothermal explosion, a non-magmatic event where superheated water flashes to steam, violently throwing mud and rock. Large hydrothermal explosions occur on average every 700 years in the region.
Methods for Monitoring Volcanic Activity
The Yellowstone Volcano Observatory (YVO) maintains an extensive network of instruments to track the volcano’s pulse in real time, ensuring that any significant changes are detected immediately. The seismic network, a crucial component, includes around 46 stations spread across the region. These stations typically record between 1,500 to 2,500 earthquakes annually, a level considered normal for the highly fractured and hydrothermally active area.
The YVO also uses sophisticated tools to measure ground deformation, which can indicate the movement of magma or water beneath the surface. Continuous GPS stations, numbering about two dozen, measure subtle changes in the ground’s elevation, often detecting movements of just a few millimeters per year. When magma or hydrothermal fluids accumulate, the ground tends to swell, and conversely, it subsides when fluids drain away.
Satellite-based radar, known as Interferometric Synthetic Aperture Radar (InSAR), provides broad-scale maps of surface movement by comparing images taken at different times. Scientists also monitor the release of volcanic gases and changes in the park’s famous thermal features. Continuous gas monitoring stations, such as one near Mud Volcano, measure gas composition, while specialized temperature probes track the activity of hot springs and geysers.
The Potential Effects of a Major Eruption
Should a full-scale, caldera-forming eruption occur, the immediate effects would be catastrophic and geographically widespread. Areas near the park would be devastated by pyroclastic flows, which are fast-moving currents of hot gas and rock fragments. The regional impact would include massive ashfall across the surrounding states of Montana, Idaho, and Wyoming.
Ash would likely cover the entire continental United States, with nearby states buried under meters of volcanic material. This ashfall would severely impact agriculture, transportation, and infrastructure across the country. Globally, the eruption would inject enormous volumes of sulfur dioxide and ash into the stratosphere, leading to a short-term cooling of the planet’s climate that could last for a decade or more.