http://www.newsweek.com/yellowstone-supervolcano-may-have-formed-completely-different-way-how-we-1043732

The Yellowstone supervolcano in Wyoming may have formed in a very different way than scientists previously thought, according to a study published in the journal Nature Geoscience.

Researchers from Virginia Tech (VT) found evidence to suggest that a vast slab of oceanic crust, or oceanic plate, wedged itself under the western portion of the North American continent around 30 million years ago, breaking into pieces in the Earth’s mantle. This process eventually led to volcanic activity on the surface and the formation of the long-dormant supervolcano—a large volcano that has had an eruption of magnitude 8 or more, the highest value on the Volcanic Explosivity Index.