[Reverend Bob]

You're right in that. One of the best books I've found on the Yellowstone caldera is WINDOWS INTO THE EARTH by Smith and Siegel. It includes a chart on page 51 that puts into perspective exactly how HUGE such an eruption can be. I can't reproduce it here, but I can copy the numbers.

Volumes, in cubic miles, of major eruptions (the last three are Yellowstone):

Mount St Helens, 1980 -- 0.24 c.m.

Pinatubo, 1991 -- 2.4 c.m.

Krakatoa, 1883 -- 4.3 c.m.

Mount Mazama, ~ 7600 ya -- 18 c.m.

Tambora, 1815 -- 36 c.m.

Island Park Caldera (West of Yellowstone), 1.3 mya -- 67 c.m.

Yellowstone, 630,000 ya -- 240 c.m.

Yellowstone, 2 million years ago -- 600 cubic miles!

Other "Yellowstone" eruptions may have been larger, but are impossible to measure. The main evidence they've left behind is in the form of the Snake River Plain. The mountains that once stood there were destoyed by successive eruptions as the Yellowstone "hot spot" moved beneath them.

[jpsb]

600 cubic miles!

Yikes! tick, tick, tick.

[Little Pig]

Don't forget the Deccan traps (~60my ago) weighing in at 12,000 cubic miles of lava(!)