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Beneath Yellowstone National Park, a vast expanse of spectacular wilderness visited by about 3 million people annually (opens in new tab)looms one of the largest volcanoes in the world.
Yellowstone’s Caldera – the cauldron-like basin at the summit of the volcano – is so colossal that it’s often referred to as a “supervolcano.” according to the Natural History Museum (opens in new tab) in London, means that it has the capacity to “produce an eruption of magnitude eight on the Volcanic Explosivity Index, discharging more than 1,000 cubic kilometers [240 cubic miles] of materials”.
To put this in perspective, the 1991 Pinatubo eruption in the Philippines, arguably the most powerful volcanic eruption in living memory, was ranked 6 on the Volcanic Explosivity Index, making it, according to the Museum of Natural History, ” about 100 times smaller than the reference for a supervolcano.”
So should we be concerned? Will Yellowstone erupt soon?
Is Yellowstone “predicted” for an eruption?
Media reports frequently state that Yellowstone is about to erupt. They claim that since the last supervolcano eruption was 70,000 years ago (opens in new tab), is bound to explode soon. But it’s not like that volcanoes works.
“This is perhaps the most common misconception about Yellowstone and about volcanoes in general. Volcanoes don’t work on timelines,” Michael Poland (opens in new tab), a geophysicist and scientist in charge of the Yellowstone Volcano Observatory, told Live Science via email. “They erupt when there’s enough magma erupting below the surface and pressure to cause the magma to rise.
“No conditions are in place at Yellowstone right now,” he added. “It’s all about the magma supply. Cut that off and the volcano won’t erupt.”
Many volcanoes go through cycles of activity and inactivity, Poland said. Most of the time, the activity of a volcano is a direct consequence of the magma supply. “Some volcanoes appear to have regular eruptions, but that’s because the magma supply is relatively constant – think of Kilauea in Hawaii or Stromboli in Italy,” Poland said.
Related: The 11 Biggest Volcanic Eruptions in History
So where does the idea that Yellowstone is “overdue” for an eruption come from?
“I suspect the idea of ​​’delayed’ comes from the concept of earthquakes,” said Poland. “Earthquakes happen when stress builds up on faults, and in many places that stress builds up at relatively constant rates due to, for example, plate movement. That being the case, you can expect earthquakes to occur at regular intervals. Of course, more complicated than that – there are a lot of variables at play – but for that reason, it makes more sense to say that a fault is ‘overdue’ for an earthquake.”
Poland also noted that “supervolcanoes” – a term he finds somewhat crude and sensationalistic – “are no more or less temperamental” than other volcanoes. So how do experts keep an eye on Yellowstone’s underground activity so that, in the event of a major volcanic eruption, warnings can be given?
“Yellowstone is very well monitored by a variety of techniques,” Poland said. “It’s covered in terms of seismicity and ground deformation. We track the temperatures of some thermal features, although this is not an indicator of volcanic activity, but of the behavior of specific hydrothermal areas. We observe the overall thermal emissions from space, collect gas and water to assess chemistry over time and track the flow and chemistry of the stream/river.”
So what might indicate that a massive eruption is imminent?
“Having thousands of earthquakes in a short period of time (a few weeks) with many events felt would be noteworthy as long as it is not a sequence of aftershocks from a tectonic event,” Poland said. “This seismicity would need to be combined with really extreme ground deformation (tens of centimeters in the same short period), park-wide changes in geyser activity, and thermal/gas emissions. The ground rises and falls normally by 2 to 3 cm [0.8 to 1.2 inches] every year, and typically there are about 2,000 earthquakes a year in the area, so it would have to rise way beyond those normal background levels.”
Although Yellowstone is relatively stable at the moment and hasn’t exhibited any unusual seismic activity lately, if it does erupt, the consequences could be extreme. Volcanologists have suggested that the branch they are most concerned about is windblown ash, which could end up covering a surrounding region 500 miles (800 kilometers) in diameter in over 4 inches (10 centimeters) of ash. That could, experts predict, result in the short-term destruction of Midwestern agriculture and would leave dozens of waterways clogged. According to the US Department of the Interior (opens in new tab), “the neighboring states of Montana, Idaho and Wyoming, which are closest to Yellowstone, would be affected by pyroclastic flows, while other places in the United States would be impacted by ashfall”. Poland added that the effects will also be felt beyond the borders of the United States.
“If there was a very large explosive eruption, it could impact the global climate by emitting ash and gas into the stratosphere, which could block out sunlight and lower global temperatures by a few degrees for a few years,” explained Poland.
Research published in the journal Science (opens in new tab) in December 2022 found that Yellowstone’s caldera contains more molten liquid rock than previously estimated. Given that volcanoes tend to erupt only when large amounts of magma are readily available, should this finding be cause for concern?
“It is [research] it really just confirms what we already know about Yellowstone,” said Poland. “The initial findings were that the magma chamber beneath Yellowstone was only 5-15% melting. The new research, which uses more advanced techniques but the same data, suggests it’s closer to 16-20% melted. The take home message is that the magma chamber is mostly solid. And that means there is much less likelihood of a consequential eruption. I find this result reassuring.”
