What the New Discovery of Ancient Super-Eruptions Indicates for the Yellowstone Hotspot

Fountain Paint Pot.
Credit: National Park Service.

Throughout Earth’s long history, volcanic super-eruptions have been some of the most extreme events ever to affect our planet’s rugged surface. Surprisingly, even though these explosions eject enormous volumes of material— at least 1,000 times more than the 1980 eruption of Mount St. Helens — and have the potential to alter the planet’s climate, relatively few have been documented in the geologic record.

Now, in a study published in Geology, researchers have announced the discovery of two newly identified super-eruptions associated with the Yellowstone hotspot track, including what they believe was the volcanic province’s largest and most cataclysmic event. The results indicate the hotspot, which today fuels the famous geysers, mudpots, and fumaroles in Yellowstone National Park, may be waning in intensity.

The team used a combination of techniques, including bulk chemistry, magnetic data, and radio-isotopic dates, to correlate volcanic deposits scattered across tens of thousands of square kilometers. “We discovered that deposits previously believed to belong to multiple, smaller eruptions were in fact colossal sheets of volcanic material from two previously unknown super-eruptions at about 9.0 and 8.7 million years ago,” says Thomas Knott, a volcanologist at the University of Leicester and the paper’s lead author.

“The younger of the two, the Grey’s Landing super-eruption, is now the largest recorded event of the entire Snake-River–Yellowstone volcanic province,” says Knott. Based on the most recent collations of super-eruption sizes, he adds, “It is one of the top five eruptions of all time.”

The team, which also includes researchers from the British Geological Survey and the University of California, Santa Cruz, estimates the Grey’s Landing super-eruption was 30% larger than the previous record-holder (the well-known Huckleberry Ridge Tuff) and had devastating local and global effects. “The Grey’s Landing eruption enameled an area the size of New Jersey in searing-hot volcanic glass that instantly sterilized the land surface,” says Knott. Anything located within this region, he says, would have been buried and most likely vaporized during the eruption. “Particulates would have choked the stratosphere,” adds Knott, “raining fine ash over the entire United States and gradually encompassing the globe.”

Both of the newly discovered super-eruptions occurred during the Miocene, the interval of geologic time spanning 23–5.3 million years ago. “These two new eruptions bring the total number of recorded Miocene super-eruptions at the Yellowstone–Snake River volcanic province to six,” says Knott. This means that the recurrence rate of Yellowstone hotspot super-eruptions during the Miocene was, on average, once every 500,000 years.

By comparison, Knott says, two super-eruptions have—so far—taken place in what is now Yellowstone National Park during the past three million years. “It therefore seems that the Yellowstone hotspot has experienced a three-fold decrease in its capacity to produce super-eruption events,” says Knott. “This is a very significant decline.”

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