Evidence of flowing lava hardened into rock found in Idaho several miles away from the site of an 8 million year old supervolcano eruption at Yellowstone. (Credit: Graham Andrews, assistant professor at California State University Bakersfield.) Enlarge

Aug. 27, 2013 — Supervolcanoes, such as the one sitting dormant under Yellowstone National Park, are capable of producing eruptions thousands of times more powerful than normal volcanic eruptions. While they only happen every several thousand years, these eruptions have the potential to kill millions of people and animals due to the massive amount of heat and ash they release into the atmosphere. Now, researchers at the University of Missouri have shown that the ash produced by supervolcanoes can be so hot that it has the ability to turn back into lava once it hits the ground tens of miles away from the original eruption.

Following a volcanic eruption, lava typically flows directly from the site of the eruption until it cools enough that it hardens in place. However, researchers found evidence of an ancient lava flow tens of miles away from a supervolcano eruption near Yellowstone that occurred around 8 million years ago. Previously, Graham Andrews, an assistant professor at California State University Bakersfield, found that this lava flow was made of ash ejected during the eruption. Following Andrew's discovery, Alan Whittington, an associate professor in the University of Missouri department of geological sciences in the College of Arts and Science, along with lead author Genevieve Robert and Jiyang Ye, both doctoral students in the geological sciences department, determined how this was possible.

"During a supervolcano eruption, pyroclastic flows, which are giant clouds of very hot ash and rock, travel away from the volcano at typically a hundred miles an hour," Robert said. "We determined the ash must have been exceptionally hot so that it could actually turn into lava and flow before it eventually cooled."

Because the ash should have cooled too much in the air to turn into lava right as it landed, the researchers believe the phenomenon was made possible by a process known as "viscous heating." Viscosity is the degree to which a liquid resists flow. The higher the viscosity, the less the substance can flow. For example, water has a very low viscosity, so it flows very easily, while molasses has a higher viscosity and flows much slower. Whittington likens the process of viscous heating to stirring a pot of molasses.

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