[blam]

"Just the yellowstone Caldera would destroy all of North America, and totally screw up the rest of the planet."

Yup.

It could have an Impact Winter like effect and possibly kill everyone on earth. The Toba Eruption 70-75,000 years ago almost did.

[Tolerance Sucks Rocks]

Presumably, it could be big enough to end the current interglacial period, even if some Americans survive the eruption and ashfall.