One of the most disconcerting moments I've ever seen in a nature documentary came a few years ago, when I watched Discovery Channel's Supervolcano—all about the, er, supervolcano located under Yellowstone National Park.
I remember the scientists talking about how they'd been looking for a caldera—the collapsed cone of an ancient volcano—in the Park for years, but hadn't found one. That is, until the day that someone looked around and realized that they couldn't see the caldera because they were standing in the middle of it. The Yellowstone caldera measures 34 miles by 45 miles, encompassing most of the Park. Meanwhile, the floor of the caldera has been swelling since 2004—as much as 10 inches in some places. That's the bad news.
The good news: It doesn't look like this supervolcano is heading for a super eruption.
Scientists think a swelling magma reservoir four to six miles (seven to ten kilometers) below the surface is driving the uplift. Fortunately, 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."
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. But 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.
Based on geologic evidence, Yellowstone has probably seen a continuous cycle of inflation and deflation over the past 15,000 years, and the cycle will likely continue, Smith said. Surveys show, for example, that the caldera rose some 7 inches (18 centimeters) between 1976 and 1984 before dropping back about 5.5 inches (14 centimeters) over the next decade.
National Geographic News: Yellowstone has bulged as magma pocket swells
Thanks to Marilyn Terrell for Submitterating
Pictured: A peaceful day in the middle of the Yellowstone Caldera