Yellowstone National Park’s caldera, which covers a 25- by 37-mile (40- by 60-kilometer) swath of Wyoming, is an ancient crater formed after the last big blast, some 640,000 years ago. The simmering volcano has produced major eruptions—each a thousand times more powerful than Mount St. Helens’s 1980 eruption—three times in the past 2.1 million years. The supervolcano has recently caused miles of ground to rise dramatically, scientists report beginning in 2004, which saw the ground above the caldera rise upward at rates as high as 2.8 inches (7 centimeters) a year.Is it poised for yet a fourth major explosion? Some 600,000 years ago there was a colossal cauldron of magma, a supervolcano, that exploded with such violence that it left an ash layer almost ten feet deep a thousand miles away in eastern Nebraska killing all plant life and covering almost all of the United States west of the Mississippi. Modern geological surveys have shown that this supervolcano erupts catastrophically every 600,000 years, and the land that supervolcano is trapped in was called by Blackfoot Indians ‘the land of evil spirits’ -what we call today, Yellowstone National Park.
A report from scientists at the University of Utah shows that the “supervolcano” underneath Yellowstone has risen at a record rate since mid 2004. Apparently, a “pancake-shaped blob” of molten rock he size of Los Angeles was pressed in to the slumbering volcano, some six miles down.
“There is no evidence of an imminent volcanic eruption or hydrothermal explosion. That’s the bottom line,” says seismologist Robert B. Smith, lead author of the study and professor of geophysics at the University of Utah. “A lot of calderas [giant volcanic craters] worldwide go up and down over decades without erupting.”
The journal Science however reported that the caldera floor of the massive volcano has risen 3 inches, per year, for the past three years. This is a rate of growth three times more rapid than ever observed, since records were first kept back in 1923.
“Our best evidence is that the crustal magma chamber is filling with molten rock,” Smith says. “But we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates again,” he adds.
Since the most recent blast 640,000 years ago, about 30 smaller eruptions—including one as recent as 70,000 years ago—have filled the caldera with lava and ash, producing the relatively flat landscape of the Yellowstone plateau we see today. According to the US Geological Survey, the rate slowed between 2007 and 2010 to a centimeter a year or less. However, since the start of the 2004 swelling, ground levels over the volcano have been raised by as much as 10 inches (25 centimeters) in places.
“It’s an extraordinary uplift, because it covers such a large area and the rates are so high,” said the University of Utah’s Bob Smith, a longtime expert in Yellowstone’s volcanism in an interview with National Geographic.
Scientists believe a growing magma reservoir four to six miles (seven to ten kilometers) below the surface is the culprit, driving the uplift. The surge doesn’t seem to herald an imminent catastrophe, Smith said.
“At the beginning we were concerned it could be leading up to an eruption,” said Smith, who co-authored a paper on the surge published in the December 3, 2010, edition of Geophysical Research Letters. “But once we saw [the magma] was at a depth of ten kilometers, we weren’t so concerned. If it had been at depths of two or three kilometers [one or two miles], we’d have been a lot more concerned.”
Smith and colleagues at the U.S. Geological Survey (USGS) Yellowstone Volcano Observatory have been mapping the caldera’s rise and fall using tools such as global positioning systems (GPS) and interferometric synthetic aperture radar (InSAR), which gives ground-deformation measurements.
Ground deformation can suggest that magma is moving toward the surface before an eruption: The flanks of Mount St. Helens, for example, swelled dramatically in the months before its 1980 explosion.
There are also many examples, including the Yellowstone supervolcano, where it appears the ground has risen and fallen for thousands of years without an eruption.
“These calderas tend to go up and down, up and down,” he said. “But every once in a while they burp, creating hydrothermal explosions, earthquakes, or—ultimately—they can produce volcanic eruptions.”
Predicting when an eruption might occur is extremely difficult, in part because the fine details of what’s going on under Yellowstone are still undetermined. What’s more, continuous records of Yellowstone’s activity have been made only since the 1970s—a tiny slice of geologic time—making it hard to draw conclusions.
“Clearly some deep source of magma feeds Yellowstone, and since Yellowstone has erupted in the recent geological past, we know that there is magma at shallower depths too,” said Dan Dzurisin, a Yellowstone expert with the USGS Cascades Volcano Observatory in Washington State.
“There has to be magma in the crust, or we wouldn’t have all the hydrothermal activity that we have,” Dzurisin added. “There is so much heat coming out of Yellowstone right now that if it wasn’t being reheated by magma, the whole system would have gone stone cold since the time of the last eruption 70,000 years ago.”
The large hydrothermal system just below Yellowstone’s surface, which produces many of the park’s top tourist attractions, may also play a role in ground swelling, Dzurisin said, though no one is sure to what extent. “Could it be that some uplift is caused not by new magma coming in but by the hydrothermal system sealing itself up and pressurizing?” he asked. “And then it subsides when it springs a leak and depressurizes? These details are difficult.”
The roughly 3,000 earthquakes in Yellowstone each year may offer even more clues about the relationship between ground uplift and the magma chamber.
For example, between December 26, 2008, and January 8, 2009, some 900 earthquakes occurred in the area around Yellowstone Lake, which may have helped to release pressure on the magma reservoir by allowing fluids to escape, and this may have slowed the rate of uplift, the University of Utah’s Smith said.
“Big quakes [can have] a relationship to uplift and deformations caused by the intrusion of magma,” he said. “How those intrusions stress the adjacent faults, or how the faults might transmit stress to the magma system, is a really important new area of study.”
Overall, USGS’s Dzurisin added, “the story of Yellowstone deformation has gotten more complex as we’ve had better and better technologies to study it.”
Casey Kazan – http://www.dailygalaxy.com, nationalgeographic.com, http://volcanoes.usgs.gov/yvo/, 2010 Swarm Summary,