Beneath Yellowstone’s geysers and hot springs lies one of Earth’s most destructive volcanoes. The Yellowstone supervolcano has erupted at least 10 times over the past 16 million years, permanently altering the geography of North America, as well as warping our planet’s climate.
And new the discovery of two ancient supereruptions — including the single largest in the hotspot’s history — reveals an unexpected result: the volcano’s activity is likely abating.
It seems the Yellowstone hotspot has experienced a three-fold decrease in its capacity to produce super-eruption events
Dr Thomas Knott
Yellowstone researchers made the discovery after analysing a new tract of volcanic rock spewed-up by the volcanic hotspot.
According to the study’s authors, the new finding rewrites the hotspot’s ancient history.
Dr Thomas Knott, a University of Leicester volcanologist and the study’s co-author, said: “It seems the Yellowstone hotspot has experienced a three-fold decrease in its capacity to produce super-eruption events.
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“This is a very significant decline.”
The Yellowstone hotspot resides beneath a 1,530 square mile (4,000 square km) stretch of Yellowstone National Park.
While the enormous heat source fuels the park’s most iconic features, such as the Old Faithful geyser, it has not always been there.
Earth’s ever-shifting tectonic plates have left a trail of ancient volcanic wreckage behind it.
The largest, most cataclysmic of these eruptions are called super-eruptions.
These Earth-shuddering blasts measure eight or higher on the Volcanic Explosivity Index (VEI), which measures a volcano’s relative explosivity by the height of its ash column and the volume of its leftover lava.
The 1980 eruption of Mount St Helens measured five on the VEI.
And because the scale is logarithmic, a level-eight super-eruption is approximately 1,000 times more explosive.
The most recent Yellowstone super-eruption occurred 630,000 years ago and formed much of the modern geography of the park.
Another eruption occurred approximately 2.1 million years ago.
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And before this, the eruption history gets murkier, with the latest research suggesting at least four other super-eruptions occurred over the past 12 million years.
Finding evidence for specific eruptions is difficult, with significant volcanic deposits tending to overlap.
The latest study saw researchers attempt the most in-depth analysis of North America’s ancient volcanic rock tracts ever conducted.
The team correlated widely-separated volcanic deposits in Idaho and Nevada with seven characteristics, including the rock’s colour, age, its chemical composition and the polarity of magnetic minerals.
The research revealed a smattering of volcanic deposits previously attributed to a series of small eruptions resulted from two gargantuan ones.
The oldest — called the McMullen Creek super-eruption — occurred approximately nine million years ago over a 4,600-square-mile (12,000 square km) stretch of what is now southern Idaho, the researchers found.
The second, called the Grey’s Landing super-eruption, occurred 8.72 million years ago and was absolutely “colossal,” the team wrote in the study.
This eruption covered roughly 8,900 square miles (23,000 square km) of what is now southern Idaho and northern Nevada — making it the single largest eruption of the Yellowstone hotspot ever detected.
Dr Knott said: “The Grey’s Landing super-eruption is one of the top five eruptions of all time.
“It enamelled an area the size of New Jersey in searing-hot volcanic glass that instantly sterilised the land surface.
“Particulates would have choked the stratosphere, raining fine ash over the entire United States and gradually encompassing the globe.”
This epic eruption appears to have been about 30 percent larger than the hotspot’s next-biggest eruption, which occurred 2.1 million years ago.
There are now six recorded super-eruptions that occurred during the Miocene epoch, between 23 million and 5.3 million years ago.
These eruptions occurred, on average, every 500,000 years, the researchers wrote.
By comparison, the two super-eruptions that occurred since then are separated by 1.5 million years.
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