Yellowstone Supervolcano May Have Formed In a Completely Different Way to How We Thought

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.

The newly proposed idea directly contradicts the long-held view that Yellowstone was produced by a plume of magma rising up from the Earth's core through rifts or weak regions of the crust. This is known as the "plume model".

A team led by Ying Zhou, a theoretical seismologist at VT's Department of Geosciences, took X-ray-like images of the Earth's deep interior with USArray—an underground "observatory" funded by the National Science Foundation.

The scientists used a technique, known as diffraction tomography, which enabled them to essentially "see" subterranean structures using the waves created by tectonic movements. When these occurred, seismometers at USArray picked up the vibrations and this data was then processed to create an image of what lies beneath the ground.

"This is the first time the new imaging theory has been applied to this type of seismic data, which allowed us to see anomalous structures in the Earth's mantle that would otherwise not be resolvable using traditional methods," Zhou said in a statement.

The Yellowstone supervolcano is also a caldera—a large hollow that's formed when a volcano collapses after a large eruption. In the case of Yellowstone, the caldera—which measures approximately 30 by 45 miles—was formed approximately 630,000 years ago following a cataclysmic eruption at Lava Creek.

The Yellowstone caldera forms part of a wider region of volcanic activity known as the Yellowstone hotspot track, which comprises a line of calderas extending across Oregon, Idaho and Wyoming.

Most volcanoes are found on the boundaries of tectonic plates, but this volcanic hotspot is located right in the middle of the North American plate. Previously the plume model has been used to explain the location of the Yellowstone hotspot track, but the researchers found no evidence for this in the latest study.

"If the North American plate was moving slowly over a position-fixed plume at Yellowstone, it will displace older volcanoes towards the Oregon-Idaho border and form a line of volcanoes, but such a deep plume has not been found." Zhou said.

Instead, the anomalous geological structure they found, which was located about 250 to 400 miles beneath the supervolcano, followed the path of the track. This indicated that when the oceanic plate—known as the Farallon Plate—broke into pieces, a section of it tore off and sank down deep into the Earth. This sinking section gradually pushed hot materials upwards to form the supervolcano, according to Zhou.

The next step for the researchers is to increase the resolution of the X-ray like images to recreate the fragmentation of the gigantic oceanic plate and test different scenarios of how magma systems fed the Yellowstone hotspot.