Out of 148 American volcanoes, the U.S. Geological Survey ranks Yellowstone's as the 21st biggest threat, Yellowstone Volcano Observatory geologist Hank Heasler said Friday.

Last year, the park experienced 1,202 earthquakes, albeit minor ones. The park's newest safety inspector had to evacuate the office after steam vents shot 4.5 percent carbon monoxide-level gas up through the floor cracks.

Five bison dropped dead in 2004 from toxic gasses emitting from the surface of the park, looking like they had been cow-tipped, Heasler said, speaking to the Wyoming Geological Association at the Petroleum Club.

"You really don't want to use one of these as a canary," he added.

Outbreaks of earthquakes, changes in gas emissions, ground deformations - they're all signs of a potential volcano eruption, and they've all occurred at Yellowstone National Park, Heasler said.

So the newspaper that ran the headline "VOLCANO DOOM," was dead on?

"So in Yellowstone all these signs are there, right?" Heasler asked, rhetorically.

Yes, but not exactly.

"All these things aren't in the same area," he said.

Heasler told the assembled geologists that his studies at the 2.2-million acre national park show that a catastrophic event like a caldera-forming volcanic eruption is the least likely to happen.

Though many geologic events and indicators happen at Yellowstone - the world's most active volcanic system - they aren't happening in such a confined area or at a rate alarming enough to predict that there's going to be a supervolcanic eruption anytime soon, Heasler said.

He told the geologists that data streaming in from the Yellowstone Volcano Observatory is available on the Internet at {M7http://volcanoes.usgs.gov/yvo.

Contact reporter Cory Matteson at (307) 266-0589 or cory.matteson@casperstartribune.net.