In a first-of-its-kind measurement of electrical conductivity, scientists have found that the plume of hot and partly molten rock that feeds the Yellowstone supervolcano may be larger than earlier believed.
Details from the University of Utah geophysicists' work was announced Monday.
"It's really neat stuff," said Bob Smith, professor emeritus and research professor of geophysics and a coordinating scientist of the Yellowstone Volcano Observatory. "We're getting an enormous amount of interest globally."
Smith co-authored the study with professor Michael Zhdanov, an expert on measuring magnetic and electrical fields on Earth's surface to find oil, gas, minerals and geologic structures underground.
In the new study, images of the Yellowstone plume's electrical conductivity — generated by molten silicate rocks and hot briny water mixed in partly molten rock — show the conductive part of the plume dipping more gently to the west, at an angle of perhaps 40 degrees, and extending perhaps 400 miles from east to west.
"It appears like a sheath around the north side of the seismic anomaly," Smith said. "It's about the conductivity of sea water."
The work complements a 2009 study done by Smith using seismic waves. That work showed the plume of hot and molten rock dipping downward from Yellowstone at an angle of 60 degrees and extending 150 miles west-northwest to a point at least 410 miles under the Montana-Idaho border — as far as seismic imaging could see. The geoelectric image can see only 200 miles deep.
Smith said the two images of the Yellowstone plume look somewhat different because "we are imaging slightly different things." Seismic images highlight materials such as molten or partly molten rock that slow seismic waves, while the geoelectric image is sensitive to briny fluids that conduct electricity.
Zhdanov and colleagues used data collected by EarthScope, a National Science Foundation-funded effort to collect seismic, ground deformation and electrical and magnetic field data to study the structure and evolution of North America. A total of 115 stations in Wyoming, Montana and Idaho collected the information.
Smith said the low-frequency measurements are made using Earth's natural electrical currents, generating reams of data. Reproducing the geoelectric plume picture took about 18 hours of supercomputer time "roughly equivalent to 200 common PCs," Zhdanov said.