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| Earth on Apr 11, 2011

Underground plume of Yellowstone supervolcano bigger than thought

Researchers used electrical conductivity to measure the plume – or area of molten rock – beneath the Yellowstone supervolcano.

The volcanic plume beneath Yellowstone National Park – hot upwellings of hot and partly molten rock that create the park’s famous geysers and hot springs – might encompass a bigger area than originally thought, according to researchers at the University of Utah.

Past images of the extent of the plume had been made using earthquake waves. The Utah researchers used a different kind of imaging technology, which measured the electrical conductivity of the molten rock that lies beneath the Yellowstone caldera – sometimes called the Yellowstone supervolcano – in northwestern Wyoming.

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.

The researchers determined that Yellowstone’s underground volcanic plume covers an area about 400 miles from east to west. This is a significant increase over the initial estimate of about 150 miles. Due to limitations in the measuring technology, researchers were not able to get a more accurate measure of the depth of the plume. The depth estimate remains at about 410 miles beneath Earth’s surface.

The top of the volcanic plume rests about 50 miles beneath Yellowstone. From there it occasionally sends globs of molten material to a chamber comprised of spongy rock located about four to 10 miles beneath the Earth’s surface. This magma chamber is what fuels the famous geysers and hot springs of the park.

Yellowstone’s supervolcano has had only three sizable eruptions over the past two million years – 2 million, 1.3 million, and 642,000 years ago. Each eruption spewed enough ash to cover half of North America. The greatest eruption produced 2,500 times more ash than the eruption of Mount St. Helens in 1980.

The new measurements of the volcanic will prove vital in predicting the destructive capabilities of Yellowstone’s slumbering giant. While stressing that doomsday is not imminent, scientists In recent years have detected an faster rate of rising for the caldera and increases in seismic activity. The U.S. Geological Survey has ranked the Yellowstone caldera as the 21st most dangerous of 169 volcano centers in the U.S.

The Utah researchers used geoelectric imaging to measure the conductivity of rocks and fluids beneath Yellowstone’s surface, increasing the estimate of the plume size. One of the limitations of the geoelectric method, however, is that it cannot probe as deeply into the Earth as the seismic method. Geophysics Professor Michael Zhdanov professor of geophysics at the University of Utah and principal author of the study, said in a press release:

It’s like comparing ultrasound and MRI in the human body; they are different imaging technologies.

So researchers have used electrical conductivity to measure the plume – or area of molten rock – beneath the Yellowstone supervolcano. It’s now known to be much larger than previously believed. Does it mean the Yellowstone supervolcano is closer to erupting than previously? No. But it does mean that scientists should be able to use this new tool to probe the characteristics of the supervolcano plume, perhaps gaining more insight into possible future eruptions.

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