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Geophysicist: Calling Yellowstone a ‘supervolcano’ is trite, misleading


CASPER, Wyo. — Geophysicist Mike Poland thinks the term “supervolcano” is overused and misleading when is comes to describing caldera systems underneath Yellowstone National Park and surrounding areas.

Poland works with the United States Geological Survey and is Scientist-in-Charge at the Yellowstone Volcano Observatory.

The USGS releases weekly “Yellowstone Caldera Chronicles” and Poland’s column was released on Monday Oct. 7.

“I have a confession to make,” Poland says. “I really don’t like the term ‘supervolcano.’ And I’d like to use this week’s edition of Yellowstone Caldera Chronicles to rant about the topic. I’d also like to propose that we use a different term.”

Poland suggests the term “caldera systems” rather than the “overused, misrepresentative and misapplied” term supervolcano.

Caldera systems “would refer to any volcano that has experienced an explosion massive enough that the surface has collapsed into a partially emptied magma chamber,” Poland says.

He says this term would aptly describe Yellowstone, Crater Lake in Oregon and “Campi Flegei” or Phlegraean Fields near Naples, Italy.

“[I]f you must use ‘super,’ use it when referencing specific eruptions—like the massive explosion from Yellowstone 631,000 years ago,” Poland adds. “That was a VEI=8 super eruption that occurred from a caldera system. See? Doesn’t that sound better?”

“VEI” refers to the “Volcano Explosivity Index.” Poland says that volcanologists call “super” eruptions “those which have generated 1000 km3 of ash and other volcanic products.”

That means a VEI=8 eruption generated 10 times more material than a VEI=7 eruption, and 100 times more than a VEI=6 eruption,” he explains. “For reference, the 1980 Mount St. Helens eruption was VEI=5. The 1991 eruption of Pinatubo, Philippines, was VEI=6.”

The above-mentioned Campi Flegrei saw a VEI=7 eruption about 39,000 years ago. As this is short of the definition of a “super” eruptions, Poland says it is a misapplication to call that caldera system a supervolcano.

“My wise colleague, Dr. Jamie Farrell, assistant research professor at the University of Utah and chief seismologist of the Yellowstone Volcano Observatory, likes to say that ‘there are no supervolcanoes, only volcanoes that have super eruptions,'” Poland adds. “I couldn’t agree more.”

He says the term supervolcano is misleading because it suggest such systems only have large-scale eruptions.

Of course, this is not true,” Poland says. “Most Yellowstone eruptions that involve magma reaching the surface are lava flows.”

“In fact, there have been about 80 lava flows of varying compositions in and around Yellowstone since the last time the system experienced a catastrophic explosion. Yellowstone is a lot more than just explosions, and calling it a ‘supervolcano’ is a gross oversimplification.”

Poland says that Yellowstone’s biggest eruption happened 2.1 million years ago, “depositing the Huckleberry Ridge ash bed.” The more recent massive eruption 631,000 years ago deposited the Lava Creek ash bed.

“These eruptions left behind huge volcanic depressions called ‘calderas’ and spread volcanic ash over large parts of North America (see map).” Poland says. “If another large caldera-forming eruption were to occur at Yellowstone, its effects would be worldwide.”

“Thick ash deposits would bury vast areas of the United States, and injection of huge volumes of volcanic gases into the atmosphere could drastically affect global climate. Fortunately, the Yellowstone volcanic system shows no signs that it is headed toward such an eruption in the near future. In fact, the probability of any such event occurring at Yellowstone within the next few thousand years is exceedingly low.”

Map of the known ash-fall boundaries for major eruptions from Long Valley Caldera, Mount St. Helens and Yellowstone. (Click image to view full size.)

Poland says the term “supervolcano” dates back to at least 1948. A geologist named Edwin Hodge has proposed a theory in 1925 “that the Three Sisters volcanic region of central Oregon was actually the site of one very large volcano, which he called ‘Mt. Multnomah.'”

Hodge’s theory was disproven by geologist Howell Williams. It was a “review of Williams’s 1948 book on Oregon volcanoes” which referred to the Three Sisters theory as a supervolcano, Poland says.

“The term lay dormant (pun intended) for decades, and was mostly absent from the scientific literature until the 2000s,” he adds. “The term ‘super eruption’ had been used, however, to describe some of the largest known eruptions on Earth, like that of Toba, Indonesia, 74,000 years ago.”

Poland says that supervolcano found its way into scientific writing in the early 2000s.

“More general and widespread use of the term exploded (so to speak) following the 2005 release of the British-Canadian docudrama ‘Supervolcano,’ a disaster television film that centered around a hypothetical large eruption of Yellowstone,” he says.

In addition to being misleading and a misapplied, Poland simply finds the term trite.

Remember back in the 2000s when people used ‘uber’ in front of a word to mean ‘very’?” he asks. “The pizza wasn’t just delicious, it was uber-delicious. The summer wasn’t hot, it was uber-hot. It was so uber-annoying!”

“Fortunately, the fad faded. The same can be said for ‘supervolcano.’ Adding ‘super’ boils a complex and important aspect of volcanology down into something that sounds like a catch phrase.”