ST. GEORGE – A research team led by geologists from Brigham Young University has discovered the remains of 17 supervolcanoes in southwestern Utah and southern Nevada that erupted, according to their appraisal, about 30 million years ago. These eruptions are among the largest known volcanic events worldwide and greatly impacted the area’s geologic history.
Located on the Wah Wah Springs tuff, a rock formation centered in Millard County, Utah, this discovery is the result of nearly 30 years of research. The fieldwork was headed by professor Eric Christiansen and Professor Emeritus Myron Best of BYU’s Department of Geological Sciences, with help from the U.S. Geological Survey and the University of California, Berkeley. Over 15 BYU students also made significant contributions to the study and dozens more assisted in the geologic mapping of the area.
Anyone expecting to hike out to the tuff and see geologic formations of epic proportion will be disappointed. Rather than the tall, conical mountains that most people expect of a volcano, the area is simply a flat expanse of nondescript desert land. In fact, its ordinary appearance has kept these massive eruptions hidden in plain sight for millennia, Christiansen said.
“These calderas are no longer evident in the landscape because of obliteration by millions of years of faulting and erosion, but the vast ignimbrite layers still reveal the enormity of these events,” Christiansen said. “Our careful work has revealed their details.”
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Video courtesy of BYU News
The Wah Wah Springs tuff is home to a group of 17 ancient volcanoes so big they are classified as “supervolcanoes.” Volcanic events in recorded history, among the most devastating being the 1883 eruption of Krakatoa and the 1815 eruption of Mount Tambora, are dwarfed by the magnitude of these explosions, which occurred mostly before the existence of human beings. Also unlike modern volcanoes, supervolcanoes typically collapse into themselves after an eruption, leaving behind a massive crater known as a caldera rather than a peak.
To be certain that their discovery was indeed on the supervolcano scale, Christiansen and his team traveled to numerous locations in mountain ranges throughout the western United States to measure the thickness of ash deposits suspected to have erupted from Utah. Then they evaluated the samples using radiometric dating, X-ray fluorescence spectrometry and chemical analysis to verify that they all came from the same source.
“Utah’s geology is fascinating and this is another chapter in its long history,” Christiansen said. “It’s a catastrophic and explosive one, but important because it is.”
The largest volcano on the tuff is the Indian Peak Caldera, approximately 35 miles wide and 3 miles deep. It is one of the biggest supervolcanoes ever discovered, and findings suggest that it erupted several times.
One explosion was among the largest known volcanic events, discharging more than 5,500 cubic kilometers of magma over a week. This eruption was about 5,000 times more powerful than the catastrophic 1980 Mount St. Helens eruption and left a significant part of Utah and Nevada buried in ash more than 1,000 feet thick, with traces found as far away as Nebraska.
“18-36 million years ago, dozens of colossal volcanic eruptions broadcast tens of thousands of cubic miles of volcanic ash across what is now (the western U.S.). This unusually intense burst of activity included some of the largest explosive eruptions known on Earth,” Christiansen said. “These pyroclastic flows move as thick clouds of hot volcanic ash that hug the surface and move at speeds of over 100 miles per hour. Individual layers of ash emplaced in the course of these eruptions are found hundreds of miles from their sources and are thousands of feet thick. Imagine the devastation.”
The staggering size of Indian Peak and neighboring calderas are comparable only to the well-known craters of Yellowstone. But unlike those volcanoes, they are not active and will never experience another eruption.
Still, much remains to be learned about the supervolcano. The Wah Wah Springs Tuff is an important discovery for not only Utah, but the world.
“Because these calderas have a number of different rocks and each one is very different and distinctive, they serve as a timeline that we can use to discover what southwestern Utah looked like over 30 million years ago,” said Bob Biek, senior scientist with the Utah Geological Survey. “They’re really important to volcanic history.”
“We’ll continue to work on this because there are many unanswered questions. Is the chamber fully empty or is there still magma left in it? Are there any ore deposits?” Christiansen said. “Other people will look at this as an example of the processes that make volcanoes and it will help them understand volcanoes and supervolcanoes.”
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