Yellowstone National Park, whose 3,500 square miles are mostly situated in Wyoming, is one of the most popular spots in the nation for nature lovers. But it also happens to sit atop a slumbering volcano with a history of massive eruptions, the most recent of which was at least 70,000 years ago.

Lately, the Internet has been rife with rumors that it's about to blow again, due to what some amateur prognosticators see as disturbing omens -- a March earthquake, an unusual release of helium from the park's hot springs and fumaroles, and bison that have been observed pushing outside the park's boundaries.

The scientists at the U.S. Geological Survey's Yellowstone Volcano Observatory reassure that there isn't anything unusual going on under the park, and that the odds are that it won't erupt for centuries. But when the volcano eventually does blow, they say, it's going to be a gigantic event that will spew enough ash to blanket the Rocky Mountains with a layer that could be several feet thick, and send particles across the entire country, with some even reaching far-away cities such as New York and Washington, D.C.

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That prediction, based upon a USGS computer model, is described in a new article in Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union. The scientists calculated that a volume of more than 200 cubic miles (330 cubic kilometers) of ash -- about 850 times the amount spewed by Mount St. Helens in 1980 -- would be released in an umbrella cloud, which would distribute it evenly in all directions.

The cloud would temporarily shut down air travel and disrupt electronic communications across North America, make roads slippery, short out electrical transformers, and cause respiratory problems for people who breathed in the dust. Over the longer term, though, the effects upon livestock and crop production in the Midwest could be worrisome as well. The dust might also temporarily cool global temperatures for a few years in a fashion similar to the Tambora eruption in 1816, which caused snow to fall in the Northeast in June.

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If it's any comfort, we're likely to have plenty of warning. Jacob B. Lowenstern, the scientist in charge of the U.S. Geological Survey’s Yellowstone Volcano Observatory, explained in a recent newspaper interview that a major eruption would be preceded by unmistakable signs such as ground deformation and multiple precursor earthquakes.

Photo: Aerial of Excelsior Geyser Crater and Grand Prismatic Spring at Yellowstone National Park. Credit: Jim Peaco, NPS