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Italy's Etna First Active Volcano to Get "CT Scan"

Richard A. Lovett
for National Geographic News
August 10, 2006
 
For the first time, scientists have watched magma move through a volcano before it erupts in fountains of ash and lava.

Using imaging methods similar to those employed in medical CT scans, researchers tracked the flow of magma in Italy's Mount Etna, which towers nearly 11,000 feet (3,350 meters) above the island of Sicily (map of Italy).

The scan, which detected areas rich in gases that produce explosive eruptions, may become a powerful tool for eruption prediction.

Scientists used 45 seismic stations positioned on the slopes of Etna to take measurements of the intermittently active volcano.

These seismic stations recorded more than 2,500 earthquakes during an 18-month interval that included one unusually violent eruption in 2002.

(Related story: "Etna Volcano Becoming Dangerous, Experts Warn" [February 6, 2003].)

The seismic waves from such earthquakes can be used to produce detailed three-dimensional images of a volcano's interior, seismologist Domenico Patanè of Italy's National Institute of Geophysics and Volcanology in Catania said in an email.

Patanè is lead author of a study that used the quake readings to make before-and-after maps during the 18-month period. The research will appear in tomorrow's issue of the journal Science.

3-D Image

The maps show the mountain's interior down to depths of three miles (five kilometers).

Such maps can be made, Patanè says, by comparing the speed with which seismic waves reach each of the stations. Different speeds mean waves are traveling through different types of rock.

This imaging technique had never before been applied to an erupting volcano.

The method allowed scientists to spot the appearance of zones where seismic waves moved unusually slowly.

These "slow" zones, the scientists say, indicate the arrival of a new batch of magma beneath the mountain. This magma is rich in carbon dioxide gas, which produces explosive eruptions.

(Related photo: Philippine Volcano Threatens Eruption [August 7, 2006].)

In essence, says Gillian Foulger of Britain's Durham University, the scientists were watching a movie of the magma moving into the volcano and up to the surface.

"They only have two snapshots," she said, "but we're moving toward a situation where we can have many snapshots that show us the progress."

In an accompanying comment in Science, Foulger calls the Italians' work an important step toward the technology presented in the 2005 Discovery Channel movie Supervolcano. In the film, scientists of the future could track magma movements and issue warnings to people likely to be in harm's way.

Study co-author Patanè agrees. "This discovery will potentially offer a powerful tool of integrated surveillance for forecasting eruptions in the middle and short term, in particular those of highly explosive nature," he said.

Powerful Technique

This type of intensive seismological mapping can also be used to study other types of subterranean features.

Foulger, for example, has used a similar method to track the effect of geothermal power generation on underground steam reservoirs at The Geysers hydrothermal site in northern California.

The results indicated that excessive power generation was depleting the underground steam, leading to changes in how the power plants are operated.

In another study, her team made a detailed seismic survey of California's Mammoth Mountain, a popular ski area that sits in a zone of restless volcanism.

At the time, there had been many small earthquakes, "suggesting that we might be building up for an eruption sometime in the future," she said.

"There was no eruption, but carbon dioxide started pouring out of the mountain at an enormous rate, killing off the forests."

She and her colleagues conducted an eight-year study there, observing how carbon dioxide gas appeared to have accumulated in some places while moving out of others.

This is useful, she says, because the movement of gases and water affects how explosive an eruption will be if one occurs.

Foulger dreams of a future in which all potentially dangerous volcanoes will be outfitted with networks of seismometers similar to the ones that allowed Patanè's research group to watch lava movements beneath Etna.

"We have the technologies, but there is often a huge reluctance to implement them until too late," she said.

"The Italian paper is very helpful, because it's a step forward in showing what is possible. Politicians and people in communities that are potentially in danger from active volcanoes should take note," she added.

"Maybe we can consider implementing it before an eruption rather than after."

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