A recent study has unveiled a new perspective on the ancient eruptions that formed the region now known as the Snake River Valley in Idaho and the Yellowstone Caldera in Wyoming. The study, conducted out of the University of Leicester, found that there were far fewer individual eruptions over the 8-to-12 million-year span that formed the region’s geography, but those individual eruptions were much more violent than originally estimated.

The new study reveals that there were 12 major eruptions over the period in question, half as many as was previously assumed. During that time, a geological hotspot slowly crept along under the crust, periodically punching it’s way to the surface, and forming the Snake River Valley in the process. This series of eruptions culminated in the eruption that formed the now famous Yellowstone Caldera 640,000 years ago. The hotspot has since moved to a point under a thicker portion of the lithosphere, making the likelihood of a new eruption very unlikely.

“While it is well-known that Yellowstone has erupted catastrophically in recent times, perhaps less widely appreciated is that these were just the latest in a protracted history of numerous catastrophic super-eruptions that have burned a track along the Snake River eastwards from Oregon to Yellowstone from 16 million years ago to the present,” explains study lead author Tom Knott, from the University of Leicester’s Department of Geology’s Volcanology Group.

The eruptions that were studied were massive: one of them, referred to as the Castleford Crossing eruption, took place 8.1 million years ago, blasting through the Earth’s crust with a force that would have registered at 8.6 on the Volcanic Explosivity Index (VEI) — thousands of time more powerful than the 1980 eruption of Mount St. Helens, ejecting over 1,900 cubic kilometers (456 cubic miles) of debris — blasting enough magma and ash into the atmosphere to fill Lake Ontario.