“Supervolcano,” we should note, is not a technical term. The experts refer to Yellowstone as a “caldera” or a “caldera-forming volcano.” Some volcanoes form conical mountains. A caldera is a volcano that creates a vast crater. These are mountain-swallowing events. Visitors to Yellowstone are given a map showing the outline of the most recent caldera, and if they go to the right vantage point, it’s possible to see that the heart of the park is remarkably free of mountains. They were either blown away or fell into the big hole.

The Yellowstone region has seen three big eruptions, the first one 2.1 million years ago, the most recent 630,000 years ago. Contrary to Internet rumor-mongering, as well as conspiracy theories about government coverups, there’s no sign that a fourth cataclysmic event is about to happen.

It’s possible, in fact, that Yellowstone is getting a bit old and tired. It may be ready for a long nap rather than a major eruption.

Ilya Bindeman, a University of Oregon geochemist and co-author of the new paper, said that Yellowstone may be “approaching the end of its evolution” because so much of the material in the upper magma chamber is recycled and re-melted after previous eruptions.

As Poland said: “How many times do you want to reheat your leftovers? At some point you’re going to say, ‘I’m not going to reheat this.’ You’ve microwaved it six times, and it’s no longer food.”

Intellectual humility is called for here: No one can say with great confidence how much magma it takes to trigger a caldera-forming eruption. Moreover, relatively small eruptions creating lava flows can happen within the Yellowstone system. The most recent was 70,000 years ago. The experts say one of these smaller eruptions is much more likely than a giant explosion. Speculation that Yellowstone is “due” to erupt catastrophically implies that the volcano behaves predictably, like a machine. Geologists know otherwise.

Yellowstone, it should be noted, isn’t the only caldera in the United States. One of the others that’s worth keeping an eye on — and the U.S. Geological Survey does just that — is the Long Valley caldera in California, near the popular ski resort of Mammoth Mountain, just east of Yosemite National Park. It erupted 700,000 years ago. A major eruption is extremely unlikely, but it could produce smaller eruptions that would be highly disruptive and dangerous, said Margaret Mangan, scientist-in-charge at the USGS California Volcano Observatory.

angan said there are seven volcanic regions in California with zones of molten rock beneath the surface. A volcanic eruption in California is roughly as likely as a magnitude 6 or greater earthquake on the San Andreas Fault, she said.

But Californians don’t worry about volcanoes. They worry about earthquakes, tsunamis and wildfires, she said. She has tried to raise public awareness of volcano hazards but says that it is hard to get much attention.

“The awareness level and preparedness level is quite low in this state,” she said. “We prepare for those large earthquake events, and we need to prepare for volcanic eruptions.”

Source: https://www.washingtonpost.com/news/speaking-of-science/wp/2018/04/20/the-yellowstone-supervolcano-is-a-disaster-waiting-to-happen/?noredirect=on&utm_term=.91fd33a9c902