Yellowstone Volcano’s last super-eruption, which occurred 631,000 years ago, was not a huge explosion. Instead, new research suggests it was a series of eruptions or multiple vents spewing volcanic material in rapid succession.
According to the US Geological Survey (USGS) Yellowstone Volcano Observatory 2022 Annual Report, published May 4, fieldwork over the past year has provided new geological evidence that “the Yellowstone Caldera formation was much more complex than previously thought.” A caldera is a large crater that forms after a volcano collapses following an eruption.
Yellowstone is one of the largest volcanic systems in the world. It sits above one of Earth’s “hot spots” – areas of the mantle where hot plumes rise and form volcanoes on the crust above. He produced three eruptions forming a caldera in the last 3 million years: the eruption of Huckleberry Ridge Tuff, 2.1 million years ago; the eruption of Mesa Falls, 1.3 million years ago; and the eruption of Lava Creek, 631,000 years ago.
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The Huckleberry Ridge Tuff and Lava Creek events are considered super-eruptions because they expelled more than 240 cubic miles (1,000 cubic kilometers) of material. The latter was responsible for the formation of the Yellowstone caldera. Mesa Falls erupted 67 m3 (280 km3) of material, so – although still about 10 times larger than the 1980 eruption of Mount St. Helens – is not considered a super-eruption.
Previous search showed that the Lava Creek super-eruption was not unexpected; deposits in the Sour Creek Dome area east of the national park suggest the giant explosion was preceded by at least one eruption. The ignimbrite (volcanic rock formed by deposits of the hot mixture of material ejected during an eruption) found at the site had completely cooled before the mapped main Lava Creek eruption.
To better understand the eruption’s timeline, scientists spent 2022 remapping and collecting samples at Sour Creek Dome.
“We have always known that there were at least two geological units [a volume of rock distinct from those surrounding it] of the eruption, and it was thought that there was little or no time interval between them”, Michael Poland, scientist in charge of the Yellowstone Volcano Observatory, told Live Science in an email. “Now we think there are more units. And we just don’t know what the time gap could have been, if any.”
So far, the team has found four previously unrecognized ignimbrite units at Sour Creek, suggesting at least four eruptive pulses. They also found two structures that appear to be eruptive vents, which may have been the source of these rocks.
“This could mean multiple vents were active and/or there was a temporal separation between eruptions,” Poland said. “But we don’t yet have the data we need to answer these questions.”
In 2020, scientists found the Huckleberry Ridge Tuff Eruption – which ejected more than twice the amount of volcanic material as Lava Creek did – was also a staggered event. Analysis of rocks at the site suggests there were three separate eruptions, with weeks to months between the first two and years to decades between the second and third.
The Yellowstone Volcano is shouldn’t burst any time soon. However, the finding that the Lava Creek eruption may have followed a similar pattern to the Huckleberry Ridge Tuff eruption could give some idea of what to expect if and when Yellowstone erupts. “These major caldera-forming eruptions may not be single events at Yellowstone, but rather have multiple phases,” Poland said.
Volcano researchers now plan to carry out detailed examinations of the newly discovered units and the boundaries between them. This will allow them to paint a more detailed picture of what the Lava Creek eruption looked like – and perhaps even what triggered it.
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