[link to yellowstone.net]

"More likely in Yellowstone than a large explosive caldera-forming eruption is eruption of a lava flow, which would be far less devastating. Since Yellowstone’s last caldera-forming eruption 640,000 years ago, about 30 eruptions of rhyolitic lava flows have nearly filled the Yellowstone Calder"

Sooo. We should hope for a lava flow if it does erupt?

Trying to find when the last lava flow eruption was.. it probably predates the native americans.