Old Faithful & The Milky Way

An eruption of Old Faithful geyser in Yellowstone National Park is seen against the backdrop of the Milky Way in this May 28 photo. The United States Geological Survey recently bumped the Yellowstone caldera up from a “moderate threat” to “high threat” in its National Volcanic Threat Assessment list.

The good news is that the Yellowstone caldera is not expected to explode in a mega eruption anytime soon.

But the United States Geological Survey recently bumped the national park up from a “moderate threat” to “high threat” in its “National Volcanic Threat Assessment list.”

Is it time to sell the house and take your chances in the Midwest’s tornado alley?

No, says Michael Poland, geophysicist and scientist-in-charge of the Yellowstone Volcano Observatory for the USGS.

“Unfortunately that ‘high threat’ language is getting confused right now in pretty spectacular ways,” Poland said Wednesday.

In the report, released last month, scientists looked at a volcano’s or caldera’s hazard potential — as in its exposure to people and property.

The Yellowstone system is ranked 21st among a long list of volcanoes across North America. Top of the list is an easy one to spot: Hawaii’s Kilauea spewing magma that has eaten up 700 houses in a nearby subdivision.

Others in the top five include Mount St. Helens and Mount Rainier in Washington, Redoubt Volcano in Alaska, and Mount Shasta in California. Those volcanoes are labeled “very high threat.”

Rankings are based on 24 factors, such as size of the largest explosion to have occurred at the volcano, the average recurrence of eruptions, what types of eruptions have taken place and whether the volcano shows signs of unrest. Exposure factors include how many people live nearby, the number of airplanes that fly overhead and nearby infrastructure.

Although Yellowstone hasn’t had an eruption in 70,000 years, its rating is based on recent history of steam explosions, observed seismic activity and the presence of a lot of people coming to visit (about 4 million visitors a year).

“The threat ranking is intended as a guide in terms of which volcanoes should be prioritized for upgrades in monitoring capabilities,” Poland said in a report for the USGS. “Yellowstone is already among the best-monitored volcanoes in the world, but we expect that the upgraded threat assessment will be helpful in refining the monitoring plan.”

A few volcanoes were dropped from the list completely because it was found that they weren’t even active and a few volcanoes were added. And a couple volcanoes changed their rank. For Yellowstone, its rank stayed the same as the original USGS report released in 2005.

A few places in Idaho — Craters of the Moon National Monument and Preserve, Hell’s Half Acre, Wapi Flow and Black Butte Crater — also appear on the USGS list toward the bottom under “low threat.”

“The listing and the report is not a notice of anything about the volcanic activity at present, it’s just a matter of the threat potential,” Poland said.

Poland said activity is not necessarily a portent of an impending eruption. In the case of Yellowstone, activity is normal.

“Volcanoes are like fingerprints — no two are alike,” he said. “Yellowstone has about 2,000 earthquakes a year. That’s normal for Yellowstone. But if we saw that many earthquakes at say Mount Rainier, we would be alarmed. That’s not normal for Mount Rainier. Just because it’s doing something does not mean it’s more prone to eruption.”

All this talk about volcanoes blowing their tops has alarmed some people.

“I had several people actually contact me that were in Oklahoma saying, ‘Oh man, I’m really worried about Yellowstone erupting,’” Poland said. “They said, ‘How can I prepare?’ I said, I’d be prepared for a tornado or a moderate earthquake if I was in Oklahoma, I wouldn’t care about Yellowstone. Tornadoes and earthquakes happen every year in Oklahoma versus something that might happen every million years.”

To read about regular updates on Yellowstone’s volcanic activities, go to volcanoes.usgs.gov/volcanoes/yellowstone.