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A super eruption at Yellowstone volcano 2.1 million years ago occurred over decades and not a single explosive event lasting hours or days, the researchers found.
Volcanologist Colin Wilson of Victoria University of Wellington in New Zealand analyzed the deposits of an ancient supereruption in Yellowstone to understand exactly how the magma and ash were ejected from the volcano.
Wilson’s work on the event that created the Huckleberry Ridge Tuff was published in Caldera Chronicles, a weekly column published by the Yellowstone Volcano Observatory, part of the US Geological Survey (USGS).
During the eruption, Wilson and colleagues mainly saw ash clouds rising into the atmosphere for miles and causing pyroclastic flows – a mass of incredibly hot and fast-moving ash, gas and lava fragments that stretched up to 100 miles. from the source.
“So much magma was evacuated that the surface of the ground around the mouths of the eruption collapsed, forming a 100 x 50 km (62 x 31 miles) caldera, one of the largest on Earth,” Wilson wrote. “The plume of the rash plume is still found on most of the western half of the stool [USA], and remnants of ignimbrite extend from Big Sky, Montana, to Idaho Falls, Idaho.
By studying the sedimentary layers of this eruption, Wilson and his colleagues were able to compile a chronology of the events that occurred at the volcano over two million years ago.
Their results show that there were time pauses between eruptive events. In one shift, enough time had passed for the snow to fall and for the weather systems to collect and deposit the ash.
They identify three main “ignimbrite units” – layers of volcanic deposits that would have been deposited over a period of days. Using these units, they were able to determine that the volcano exploded, stopped, cooled, and then exploded again. The time between the first two events was likely several months, Wilson said. It would take years, if not decades, before the next eruptive event occurs, with deposits indicating that there was a much longer cooling period before the next ignimbrite unit was formed.
He said that if people had been present during this eruption, they would not have witnessed a massive eruption but several minor events over the course of many years. “Although the enormous amounts of material that formed the ignimbrite units and the extensive fall deposits associated with them exploded, the eruption stopped twice, both for periods of time that, although geologically negligible, would have been highly relevant to human interests, due to the effects of repeated risks and disruptions in recovery efforts, “Wilson wrote.
Understanding how excessive eruptions at Yellowstone volcano occur is important for disaster preparedness. The last caldera-forming eruption occurred over 640,000 years ago, while the most recent volcanic activity in the form of rhyolithic lava flows occurred about 70,000 years ago.
Earlier this year, a team of researchers announced that they had discovered the largest eruption ever to occur in Yellowstone, a massive explosive event that occurred about 8.7 million years ago and covered an area the size of of New Jersey with volcanic glass. The same research showed that eruptions in Yellowstone have gotten smaller over time, possibly indicating that the activity of hot spots in the area “may be decreasing.
Wilson said their findings at Huckleberry Ridge Tuff have implications for future eruptions: “These finds change the way we think about the massive Yellowstone explosions – they can be composed of several smaller events, and this would have a significant impact on our understanding. of these eruptions and their impact on the landscape, “he wrote.
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