Could Yellowstone supervolcano be about to erupt again?

Yellowstone supervolcano’s last eruption covered most of what is now the USA in volcanic ash and lava that flowed for hundreds of kilometres.

It left a 70 by 45 kilometre-wide crater with geysers spewing jets of water that’s sometimes hotter than boiling point.

That was 640,000 years ago. Since then, it’s become home to wolves, bears, elk, 150 species of bird like the bald eagle, and the last free herds of American bison.

With major eruptions estimated to occur every 700,000 years, scientists are wondering whether Yellowstone will soon blow again.

Despite the tranquility of the 8,900 square kilometre national park’s rivers, canyons, forests and ice-capped mountains, volcanic activity is stirring.

As many as 3,000 earthquakes each year rock Yellowstone, where vast chambers of magma – molten rock – lie between 4km and 47km beneath the surface.

Up to 489 cubic kilometres of the stuff is close to the Earth’s surface. In some places, its pressure it pushing the Earth up.

One type is basalt magma, a dense but highly mobile form of molten rock that rises up from the mantle deep blow.

Another is the thicker, slower rhyolite melt, associated with explosive eruptions, of which there is about 440 square kilometres.

That’s ‘an estimated melt volume that is one to four times greater than the eruptive volume of the largest past caldera-forming eruption’, a new United States Geological Survey (USGS) noted.

But the subterranean reservoirs are scattered, and they’re far less full as previously imagined.

‘When we used magnetotellurics, we were able to see, actually, there’s not a lot there’, said Ninfa Bennington, a research geophysicist at the Hawaiian Volcano Observatory and lead author of the study recently published in the Nature journal.

‘There are these segregated regions where magma is stored across Yellowstone, instead of having one sort of large reservoir.’

What this means is that Yellowstone is unlikely to erupt anytime soon – not for another few hundred thousands years, the researchers predict.

But if it does, it won’t be quite as vast and destructive as previously imagined.

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