Scientists looking for a greater understanding of what causes supervolcanoes to erupt have come to an unsettling conclusion: They can erupt spontaneously and without any external trigger.
Researchers based at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, sought to understand what external impacts -- like an earthquake, for instance -- would trigger the eruption of a supervolcano, such as the one in Yellowstone National Park in Wyoming. Instead of trimming down the list of causes, however, scientists concluded the buildup of magma alone was sufficient to bring about its own eruption.
"We knew the clock was ticking but we didn't know how fast: what would it take to trigger a super-eruption?" explained Wim Malfait, a researcher from ETH Zurich, to the BBC. "Now we know you don't need any extra factor - a supervolcano can erupt due to its enormous size alone... Once you get enough melt, you can start an eruption just like that."
Unlike normal volcanoes, their larger "super" cousins are much more explosive, capable of erupting at least 240 cubic miles of magma. Compared to a standard volcano, which has a rigid magma chamber and therefore erupts more often as it fills up, a supervolcano's reservoir is much more elastic and therefore more difficult to predict.
To determine what might cause those large reservoirs to erupt, scientists recreated a miniature version of one in their labs, then used X-rays to analyze its structure, a release states. Put simply, they found the magma was capable of rising up through the Earth's surface and erupting entirely on its own, without any external trigger.
"The effect is like the extra buoyancy of a football when it is filled with air underwater, which forces it to the surface because of the denser water around it," explained team member Jean-Philippe Perrillat, according to RT. "If the volume of magma is big enough, it should come to the surface and explode like a champagne bottle being uncorked.”
Those conclusions are complemented by the findings of a second group of researchers, led by Luca Caricchi, of the University of Geneva, who ran 1.2 million computer simulations of supervolcanoes erupting. They, too, report that supervolcanic eruptions are directly related to the buoyancy of magma rising up through the Earth's crust.
Fortunately, compared to their common counterparts, supervolcanic eruptions are incredibly rare. Per the U.S. Geological Survey, the last recorded explosion occurred 74,000 years ago in Indonesia. The agency calculates the yearly probability of a Yellowstone eruption at 1 in 730,000, or 0.00014 percent. (There are only 20 known supervolcanoes on Earth, reports the BBC.)
"It's not something that we should worry about in our personal lives," Malfait explained to New Scientist. "It's just as a species we will have to deal with this at some point."