The good news is, Yellowstone National Park isn’t going to explode any time soon. Instead, the "supervolcano" that lies beneath America’s first national park is merely creaking and groaning, according to a group of scientists at the University of Utah. Despite measurements that show the floor of the huge Yellowstone caldera—a roughly 40-mile by 25-mile oval volcanic crater—has risen almost 3 inches per year since 2004, Utah seismologist Robert B. Smith said, "There is no evidence of an imminent volcanic eruption or hydrothermal explosion."
For decades the caldera inhaled and exhaled almost imperceptibly like a giant torso, which the volcanic bowls may do for tens of thousands of years before they finally erupt. But Smith’s team’s recent measurements showed the Yellowstone earth rose a total of 7 inches over the 30-month study period—three times more than that observed since the first measurements were taken in 1923. The question was why? What was going on below the Earth’s surface to cause the rapid upheaval?
Smith and his team are part of the Plate Boundary Observatory, a U.S. government project that operates 12 continuously recording GPS stations in Yellowstone and several hundred throughout the west to monitor ground movement. The ground stations receive timed signals from satellites, which makes it possible to measure precisely the timing and degree of uplift. From July 2004 through 2006, the scientists took data from the GPS instruments as well as radar waves bounced off the caldera floor from a satellite.
"Our best evidence is that the crustal magma chamber is filling with molten rock," Smith said. "But we have no idea how long this process goes on before there is either an eruption or the inflow of molten rock stops and the caldera deflates again."
With half of the Earth’s geothermal features, Yellowstone holds the planet’s most diverse and intact collection of geysers, hot springs, mudpots, and fumaroles. Its more than 300 geysers make up two-thirds of those found on Earth. These popular landmarks are fueled by a vast underlying volcanic system that includes what geoscientists call a "hot spot"—a gigantic plume of hot and molten rock just 30 miles under ground. Literally like a lava lamp, molten blobs sometimes detach bubble upward and into a space called the magma chamber only 5-10 miles below the surface.
Based on their measurements, Smith, study leader Wu-Lung Chang, and other volcano experts conducted computer simulations to determine what changes in the shape of the underground magma chamber best explained the recent uplift. The models suggest molten rock bubbled up into the magma chamber and spread out to form a thin horizontal slab about the size of Los Angeles, which in turn pushed up the caldera floor.
An alternate theory is that pressure from steam and hot water sometimes contributes to the uplift of the Yellowstone caldera, but Chang and his coauthors say in an article in the journal Science, "We thus suggest that the 2004-2006 episode of accelerated inflation occurred in response to a caldera-wide magma recharge of the Yellowstone volcanic system."
Among those who study volcanoes, the Yellowstone hot spot is notorious. It arrived under the Yellowstone area later than 4 million years ago and, in the meantime, has produced massive eruptions thousands of times bigger than the 1980 eruption of Mount St. Helens. Its largest eruptions buried as much as half the continental United States in several inches of volcanic ash.
The last giant eruption produced the caldera after the release of huge amounts of material caused the volcano to collapse into a giant crater where it has stayed relatively quiet for the past 70,000 years.
As for the current uprising at Yellowstone, "the uplift is still going on today but at a little slower rate," said Smith. And there is no way to know when it will stop, he said.
—Leslie Fink, NSF
The research was funded by the National Science Foundation, the U.S. Geological Survey and the Brinson Foundation. This report is provided by the National Science Foundation, an independent federal agency that supports fundamental research and education across all fields of science and engineering, in partnership with U.S. News and World Report.