[cripplecreek]

It might beat known eruptions today but the Siberian mantle plume eruption consisted of lava flows across pretty much all of Siberia.

The Indian mantle plume eruption was another big one about the time of the dinosaur extinction. (They had a couple of rough years)

[Eric in the Ozarks]

At some point, there was a volcano in what is now Arkansas. The Crater of Diamonds State Park is a volcanic pipe, said to be 95 million years old.

[gleeaikin]

I am not sure if it is not also surpassed by Toba, about 74,000 years ago. I tried to find volume ejected data, but the only figure I came up with was that it ejected 20 to 50 time what Tambora did in 1815. I think also that one of the 3 Yellowstone events also was bigger than 1,000 cubic miles in volume.