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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. Yellowstone'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.
Since then, 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 we see today.
Still, since the start of the 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.
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."
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.
When the rate of increase slows, the theory goes, the magma likely moves off horizontally to solidify and cool, allowing the surface to settle back down.
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.
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.
If it erupts, scientists say it's be more powerful than 60 million atom bombs...It could wipe out over 60% of life on Earth...oh, it gets better...including the entire US continent...