April 15, 2011

Scientists Map Volcanic Plume Under Yellowstone

The composition of a vast plume of hot rock and briny fluid 200 miles beneath Yellowstone National Park's surface has been mapped, a soon-to-be published study says.

Researchers are able to receive a clear picture of the type of material that activates Yellowstone's volcanic features through these "geoelectric" images of the plume, says study co-author Robert B. Smith, professor emeritus at the University of Utah and coordinating scientist of the Yellowstone Volcano Observatory.

"This is the first time that an electrical image has been made of a plume anywhere in the world, period," he says.

The "geoelectric" technology has been used in the past, says assistant professor at the Colorado State University, Derek Schutt, but not like this. He says that "the technology is a useful supplement to seismic measurements and will lead to a better understanding of how the earth is forming," reports the AP.

"I think what this will be particularly useful for is we can understand much better the magma distribution of what's under Yellowstone," Schutt told the news agency.

Scientists will get a better understanding of the evolution of these hot spots from the information gathered. Hot spots are a major part of continental drift and are found to be active in at least 20 places around the world from Hawaii to Iceland.

"We're getting much more information on the composition and evolution of the earth," says Smith.

Solid rock, partly molten rocks and briny fluid that conduct electricity similar to seawater make up the plume, Smith and principal author geophysics professor Michael Zhdanov of the University of Utah say.

In a previous study, seismic waves were used to measure and create a three-dimensional image of these hotspots. The 2009 images revealed that the plume dips downward from Yellowstone at a 60 degree angle and extends about 150 miles west-northwest to a point at least 410 miles under the Montana-Idaho border.

The new study found that the plume extends 400 miles from east to west and rises from the earth's depths at a 40-degree angle. However, the technology limits the image to only about a depth of 200 miles.

Nevertheless, the new data allows scientist their first detailed look at the plume image from the 2009 study. Together the seismic and electrical conductivity revealed that the plume is larger and contains more brine and fluid than previously thought.

"All this is very important to better understand the physics of this plume," Zhdanov says.

"We are just learning. It's a very new phenomenon and now we've got another tool to get an image and better understanding of the composition and geographical shape," which may help us to one day develop a way to better predict eruptions and other volcanic activity, he says.

Millions are drawn to Yellowstone's bubbling pots and spouting geysers each year. Its caldera, a 37-by-25-mile volcanic attraction at the center of the park, has erupted three times since the North American continent drifted over the hot spot, the last eruption occurring 642,000 years ago, reports the AP.

The research has yet to predict a chance for another large eruption at Yellowstone.

So far, the plume has stopped rising at about 60 miles below the earth's surface. Then some of the melted rock is leaked up through possible rock fractures to a chamber that is about five miles below the surface of the caldera, says Smith. The volcanic activity on the surface is fed by this magna chamber.

Zhdanov says that if enough of the plume breaks off and rises into the chamber, an eruption could happen. However, there is no indication of when it could occur, as the accumulation happens at a very slow pace over thousands of years.


Image 2: This image, based on variations in electrical conductivity of underground rock, shows the volcanic plume of partly molten rock that feeds the Yellowstone supervolcano. Yellow and red indicate higher conductivity, green and blue indicate lower conductivity. Made by University of Utah geophysicists and computer scientists, this is the first large-scale "geoelectric" image of the Yellowstone hotspot. Credit: University of Utah

Image 3: This illustration compares two views of the volcanic plume that feeds the supervolcano at Yellowstone National Park. The "geoelectric" image on the left is a new one based on variations in electrical conductivity of rock and fluids underground. It shows the plume dipping about 40 degrees to the west, and the method can only "see" the plume to a depth of about 200 miles. The more conventional seismic image on the right was made using earthquake waves. The seismic image shows the volcanic plume dipping 60 degrees to the west-northwest and the plume reaches a depth of at least 410 miles (this image doesn't go that deep). Together, the two images suggest then Yellowstone hotspot plume is bigger than had been thought based in the seismic image alone. Credit: University of Utah


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