|Oh. There it is.|
Here's where it gets a little scary. Last time Yellowstone erupted in any way was a lava flow about 70,000 years ago. Last time it went totally berserk was about 640,000 years ago. So...we're about due for a big one. And recent studies have shown the caldera moving upwards more quickly than ever. So there's something to think about.
Oh, and one more thing - Yellowstone is only one of six known supervolcanoes.