One of eruptions was the largest and hottest ever Yellowstone explosion on record and both date back roughly 8.7 million years ago. However, despite the size and ferocity of supervolcano eruptions, scientists have so far struggled to examine what effect they might have on the environment and the Earth’s crust.
According to the study, this is because super-eruptions are so rare in the geologic record that researchers have been unable to say exactly when they occurred or how.
But a new method of recognising super-eruptions has been tested on the field by researchers from the UK’s University of Leicester School of Geography, Geology and the Environment.
As a result, the scientists discovered there had been two previously unrecognised super-eruptions.
The study stated: “Two new catastrophic super-eruptions were discovered.”
These were identified as a magnitude 8.6 eruption from McMullen Creek, and a magnitude 8.8 eruption from Grey’s Landing.
The team identified this latter incident as “the largest known eruption on the Yellowstone hotspot track”.
The two eruptions scattered “unusually hot” volcanic matter, sterilising “extensive tracts” of the US states of Idaho and Nevada.
But the new discoveries actually suggest the number of super-eruption incidents in the Yellowstone area is decreasing.
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“The average super-eruption frequency after the Miocene has been just 1 per 1550 k.y. For example, the most recent super-eruptions at Yellowstone are separated by 1.5 m.y.
“This represents a threefold decrease in super-eruption productivity over time.”
According to geologist Erin Martin-Jones, supervolcano eruptions are so huge that their deposits cover areas tens of thousands of square kilometres, and this can make it difficult to tell each eruption apart.
To get around this problem, the researchers collected detailed information about the chemical makeup of the supervolcano deposits.
Ms Martin-Jones told science new site Massive Science this allowed them to discover that much of the debris previously thought to have come from other, small eruptions actually had the same chemical composition and age, showing they had come from two previously unknown super-eruptions.
The Leicester team hope their method of researching could lead to more discoveries in other locations.