Yellowstone’s supervolcano is essentially a giant, lid-topped cauldron, and it’s so vast that it can only truly be seen from low-Earth orbit. Its crater is 72 kilometers (45 miles) across, and its underlying plumbing contains several tens of thousands of cubic kilometers of magmatic material.
What would happen if much of this suddenly re-emerged in a horrific supervolcanic eruption? Who would live, who would die – and would the United States of America survive? We spoke to one of the country’s most respected volcanologists to get the most up-to-date low-down on the future of the world’s most famous supervolcano.
Right now, the two-step magma chamber is in a state of dormancy. According to Yellowstone Volcano Observatory’s Scientist-In-Charge, Dr Michael Poland, it may not have enough energy at present to produce a supereruption. "Right now, much of Yellowstone's magma body is partially solidified, and you need a lot of magma to feed a large eruption."
Throughout most of its life, the region has featured extensive lava flows or (far more frequently) hydrothermal blasts, which suggests that any future eruption is far more likely to replicate this. Although these will cause a problem, they certainly won’t be anything apocalyptic – and even these eruption types are exceedingly rare.
The chances of a supervolcanic paroxysm are currently around one-in-730,000, which makes it less likely than a catastrophic asteroid impact.
However, a sudden injection of new magma from beneath, or a sudden weakening of the geological layers encasing it, as unlikely as this is, may be enough to trigger a sudden depressurization event, and the entire system would violently expunge onto the surface and up into the atmosphere.
What happens next is somewhat speculative, but Yellowstone’s frightening history gives us a clue. We’re thinking about the worst-case scenario here, so let’s assume its entire magmatic belly is emptied in a colossal supervolcanic explosion.
This has happened at Yellowstone three times on a cycle of 660,000-800,000 years: 2.1 million years ago, 1.3 million years ago, and 640,000 years ago.
The most explosive eruption was its first, which produced about 2,500 times the amount of volcanic material as the 1980 destruction of Mount St Helens. Even the most recent blast created an eruptive column so colossal that it coated about 60 percent of the contiguous United States in thick layers of ash.
So let’s say that the original record-holding blast was to happen again: What would happen to the United States and the wider world?