underground Yellowstone "supervolcano"

It's like something one of those disaster movie trailers with a basso profundo voiceover: Man, or perhaps woman, on a family vacation takes in the breathtaking scope of nature found in Yellowstone National Park--only to see the earth beneath their feet violently explode. Will our hero and his or her family be swallowed in the molten horror of -- "Supervolcano"?

But this scenario isn't the stuff of Hollywood fantasy--scientists caution that there's a chance that Yellowstone could blow. One day, anyway.

Yes, there apparently exists an underground volcano whose past eruptions -- the last one estimated at some 640,000 years ago -- have been, according to National Geographic, "a thousand times more powerful thanMount St. Helens's 1980 eruption." The supervolcano lurks a few miles underground and spreads out across an area roughly the size of Los Angeles. But here's the best part: It's taking deep "breaths," as the magazine puts it, causing miles of ground around it to rise dramatically. Since 2004, researchers say that the ground above the supervolcano rose as much as 2.8 inches per year.

Here's a video from National Geographic explaining more:

So is the "swelling magma reservoir" ready to blow? Well, scientists say it will eventually--and when it does it could spew ash as high as 25 miles into the air, rendering an estimated two-thirds of the country uninhabitable. Remember, it was a massive volcanic eruption that some scientists think wiped out the dinosaurs. And here we thought that Icelandic volcano last year was a major calamity.

See below for National Geographic's photos (full slideshow here; article here); photos taken by Mark Thiessen on assignment for National Geographic magazine's August 2009 issue.

Click image to see Yellowstone's Supervolcano

National Geographic