Nov. 8, 2007 -- The turmoil beneath Yellowstone's "supervolcano" is raising the land as much as 2.8 inches per year, new ground measurements show. But the inflating land is not about to erupt, assured geologists, despite the caldera's ancient history of massive explosions.
The "supervolcano" is really a caldera, a basin-shaped volcanic feature formed in the wake of a large eruption. Spanning roughly 925 square miles in the northwest corner of Wyoming, the Yellowstone Caldera is thought to erupt every few hundred thousand years, but its exact origins remain a mystery.
What can be said is that the recent swell of the land there fits into a larger history of rises and falls that have been underway for a lot longer than geologists have been around to make sense of them, explained geologist Robert Smith of the University of Utah in Salt Lake City. He, Wu-Lung Chang and other colleagues report on the most recent changes at the famous volcanic park in the Nov. 9 issue of the journal Science.
The latest episode began in mid-2004 in the Sour Creek area of the Yellowstone Caldera, just north of Yellowstone Lake. There the swelling is the sharpest yet recorded. The previous six years had seen the land sinking at 1/3 inch per year, the team reported.
"What we know is that we have some intrusion of melt," said Smith, referring to the upward movement of hot, melted rock from around 6 miles underground. That melt is coming out of a large, cooling blob of magma that Smith and his colleagues spotted directly under the geyser-rich caldera using 3-D seismic imaging techniques.
The rising heat from that blob, plus the upward flow of some molten materials, are the most likely explanation for the swelling surface, as detected by a network of Global Positioning System stations in the park.
Smith said he hopes that a recent gravity survey -- conducted on a shoestring budget -- will help them sort out exactly what is moving, and where, underground. Gravity measurements allow geologist to detect how masses change underground by the tiny changes in gravity at any given spot on the surface.
And even though there is no mountain of magma about to erupt, the study of Yellowstone is central to understanding caldera-type "supervolcanoes" worldwide, said geologist David Hill of the U.S. Geological Survey in Menlo Park, Calif. Hill's job is to monitor California's version of Yellowstone -- the Long Valley Caldera east of Yosemite National Park.
"Any time we see one of these unrest episodes we learn about the processes that drive it," said Hill. For instance, calderas have been known to rise nearly several feet without erupting, he said. "That's a lot more uplift than we see before eruption on central vent volcanoes," he said, referring to the deadly blasts from single-maw volcanoes like Vesuvius, Pinatubo or St. Helen.
Calderas, by comparison, cover a lot more ground than central-vent volcanoes and have many vents from which they could pour ash and lava, said Hill. As a result, even a relatively small eruption from a caldera is much harder to predict and plan for because it's hard to know where in the caldera the magma will burst out.
Related Links:
Larry O'Hanlon's blog: Earth Impacts
our sites
video
mobile
shop
stay connected
corporate
