The formation of the supervolcano underneath Yellowstone is a matter of heated debate among geologists and volcanologists. The (relatively) recent formation of the hotspot has people wondering how it came to be. The main suspicion was a plume of hot material coming directly from the inner layers of the planet, but new research suggests something different.

Professor Ying Zhou, from Virginia Tech, has suggested that an ancient oceanic plate might be the cause of the hotspot. As reported in Nature Geoscience, the researchers used seismographic data to reconstruct an “image” of what the Earth beneath Yellowstone looks like. She discovered something anomalous between 400 and 640 kilometers (250 and 400 miles) underneath the region.

This peculiar structure is part of the Farallon plate, an ancient oceanic plate that sunk underneath the North American plate millions of years ago. By sinking down toward the mantle, the plate pushed hot material towards the surface, thus generating massive melting in the crust that ultimately led to the formation of the supervolcano, according to Zhou.

"In this research, there was no evidence of heat coming directly up from the Earth's core to power the surface volcano at Yellowstone," Zhou said in a statement. "Instead, the underground images we captured suggest that Yellowstone volcanoes were produced by a gigantic ancient oceanic plate that dove under the Western United States about 30 million years ago. This ancient oceanic plate broke into pieces, resulting in perturbations of unusual rocks in the mantle which led to volcanic eruptions in the past 16 million years."

The behavior of Yellowstone is extremely “plume” like. It is at the end of a hotspot track of volcanos, something that a plume would form as the tectonic plate moves above it. This is something witnessed in Hawaii. But the presence of a plume has not been confirmed, and Zhou argues that it’s not there at all. The hotspot track is created by the Farallon plate moving underneath the North American plate.

"The next step will be to increase the resolution of the X-ray-like images of the underground rock," she added. "More detailed images of the unusual rocks in the deep earth will allow us to use computer simulation to recreate the fragmentation of the gigantic oceanic plate and test different scenarios of how rock melting and magma feeding system work for the Yellowstone volcanoes."

The evidence for a model without the plume is compelling, but it is not the final word on the matter. It is possible for both models to coexist. Hopefully, future work will provide an answer to the origin of Yellowstone once and for all.