By Chris Woolston

Much of northwest Wyoming sits in a giant caldera, or volcanic crater, that last blew up in a big way 640,000 years ago, burying the Midwest in several feet of ash. Every geyser and mud pot in Yellowstone National Park reminds us that the volcano is still rumbling. Chuck Wicks of the U.S. Geological Survey uses satellite radar to keep tabs on it—from the safety of Menlo Park, Calif. volcanoes.usgs.gov.

Q What’s going on in the Yellowstone crater now?
A The entire caldera—28 miles wide, 47 miles long—has risen six inches in the last two years. Hot magma is pushing its way up. We don’t know if that’s normal. We’ve been able to track it carefully only since the mid-1990s. Every time we look, it’s doing something different.

Q Are the geysers picking up steam?
A They grew more active between 2000 and 2003, especially in the Norris Geyser Basin, but they’ve since quieted down again. We don’t know why.

Q Will Wyoming have another cataclysmic eruption?
A We think so. The question is when.

Q If it erupts, how big will the blast be?
A About 1,000 times bigger than Mount St. Helens. The Midwest would get buried again.

Q Would there be some warning signs?
A We could be seeing early signs now. If an eruption were really on its way, we would also expect to see a lot of earthquakes.

Q Would anyone have time to escape?
A The magma would have to break through six miles of crust. People would probably have a few months to evacuate.

Q Should locals think about moving?
A They shouldn’t worry. The human life span is so short compared to geologic time. Someone emailed me to ask if it was safe to move to Buffalo, Wyo. I said Buffalo is a beautiful place. I’d rather live there than here.