Below Yellowstone National Park, a vast region of spectacular wilderness visited by around 3 million people every year (opens in new tab)lurks one of the largest volcanoes in the world.
Yellowstone’s caldera — the cauldron-like basin at the top of the volcano — is so colossal that it’s often referred to as the “supervolcano” that according to the Natural History Museum (opens in new tab) in London means it has the capacity “to generate an eruption of magnitude eight on the Volcanic Explosivity Index and discharge more than 1,000 cubic kilometers [240 cubic miles] of the material.”
To put this in perspective, the 1991 eruption of Mount Pinatubo in the Philippines, arguably the most powerful volcanic eruption in living memory, was rated a 6 on the Volcanic Explosivity Index, making it “about 100 times smaller” than, according to the Natural History Museum the benchmark for a supervolcano.”
So should we be worried? Will Yellowstone erupt soon?
Is Yellowstone “due” for an eruption?
Media reports have often claimed that Yellowstone will erupt. They claim that was the last eruption of the supervolcano 70,000 years ago (opens in new tab), it will definitely blow soon. But it is not like that volcanoes Work.
“This is perhaps the most common misconception about Yellowstone and volcanoes in general. Volcanoes don’t work on timelines.” Michael Poland (opens in new tab), a geophysicist and senior scientist at Yellowstone Volcano Observatory, told Live Science in an email. “They erupt when there is enough eruptable subsurface magma and pressure to cause that magma to rise.
“Yellowstone has no requirement at this time,” he added. “It’s all about that magma pool. Stop that and the volcano will not erupt.”
Many volcanoes go through cycles of activity and inactivity, Poland said. Most of the time, the activity of a volcano is a direct result of the magma supply. “Some volcanoes seem to erupt regularly, but that’s because the magma supply is relatively constant — think Kilauea in Hawaii or Stromboli in Italy,” Poland said.
See also: The 11 Largest Volcanic Eruptions in History
So where does the idea that an eruption in Yellowstone National Park is “overdue” come from?
“I suspect that the ‘overdue’ idea comes from the concept of earthquakes,” Poland said. “Earthquakes occur when stresses accumulate on faults, and in many places these stresses accumulate at relatively constant rates, for example due to plate motion. In this case, earthquakes might be expected to occur at reasonably regular intervals. It is, of course, more complicated than that – there are many variables involved – but for that reason it makes more sense to say that a failure is ‘overdue’ for an earthquake.”
Poland also noted that “supervolcanoes” – a term he feels is somewhat crude and sensational – are “no more or less spirited” than other volcanoes. So how do experts keep a close eye on Yellowstone’s subterranean activity to provide alerts in the event of a major volcanic eruption?
“Yellowstone is very well monitored through a variety of techniques,” Poland said. “It’s covered in terms of seismicity and ground deformation. We’re tracking that temperatures of some thermal features, although this is not an indicator of volcanic activity but rather of the behavior of certain hydrothermal areas. We look at the total thermal emissions from space, collect gas and assess water Chemistry over time and track stream/flux flow and chemistry.”
So what could indicate that a massive eruption is imminent?
“Having thousands of earthquakes in a short period of time (few weeks) with many felt events would be remarkable as long as it is not an aftershock sequence of a tectonic event,” Poland said. “This seismicity would need to be coupled with truly extreme ground deformation (ten centimeters over the same short period of time), park-wide changes in geyser activity, and thermal/gas emissions. The floor usually rises and falls by 2-3 cm [0.8 to 1.2 inches] every year, and there are typically around 2000 tremors a year in the region, so it would have to be well above these normal background levels.
While Yellowstone is relatively stable at the moment and hasn’t shown any unusual seismic activity recently, the consequences of an eruption could be extreme. Volcanologists have suggested that the ramification they are most concerned about is windblown ash, which could eventually blanket a surrounding region 500 miles (800 kilometers) across with more than 10 centimeters of ash. Experts predict that this would lead to the short-term destruction of agriculture in the Midwest and clog dozens of watercourses. According to the US Department of the Interior (opens in new tab)“The surrounding states of Montana, Idaho and Wyoming, closest to Yellowstone, would be affected by pyroclastic flows, while other locations in the United States would be affected by falling ash.” Poland added that the impacts also transcend borders of the United States would be felt.
“If there were a very large explosive eruption, it could affect global climate by releasing ash and gas into the stratosphere, which could block sunlight and lower global temperatures by a few degrees for a few years,” Poland said.
Research results published in the journal Science (opens in new tab) in December 2022 found that the Yellowstone caldera contains more liquid molten rock than previously thought. Given that volcanoes tend to erupt only when a large amount of magma is readily available, should this finding be cause for concern?
“This [research] really just confirms what we already know about Yellowstone,” said Poland. “Initial results were that the magma chamber beneath Yellowstone was only 5-15% molten. The new research, using more advanced techniques but the same data, suggests it melted closer to 16-20%. The take-home message is that the magma chamber is mostly solid. And that means the likelihood of a follow-on eruption is far less. I find this result reassuring.”