Study could boost forecasts for Vesuvius eruptions

By Michael Kahn

LONDON (Reuters) - The magma pool feeding the Italian volcano that destroyed Pompeii in AD 79 has shifted in the past 2,000 years, a discovery that could help in predicting future eruptions, researchers said in the journal Nature.

Vesuvius is in southern Italy near Naples, one of the most densely populated volcanic regions in the world. Its crater is 1,280 meters (4,200 feet) above and 20 km (13 miles) away from Naples, Italy's third largest city.

Scientists had thought the pool remained constant over the past 4,000 years but new investigations detailed on Wednesday showed the chamber had actually shifted higher between the Pompeii eruption in AD 79 and the Pollena one in AD 472.

Knowing the location of the lava pool is important because more pressure builds up the deeper a pool is, resulting in more powerful eruptions, said Michel Pichavant, a geologist at the University of Orleans in France, who worked on the study.

The findings can help build more accurate models to predict damage from future eruptions by factoring in the movement of these pools, he said.

"We found that there was a substantial variation of the reservoir that is the source of a mass of lava," Pichavant said in a telephone interview.

"These variations need to be documented if we want to make reliable forecasts of future eruptions."

Although Vesuvius has slept for more than six decades, scientists fear the next big eruption could rival the one in AD 79, which suffocated the ancient cities of Pompeii and Herculaneum in ash and killed about 16,000 people.

An Italian study in 2007 suggested that 300,000 people living near the volcano would be killed the next time it erupted if they were not evacuated in time.

Pichavant and colleagues gathered rock samples from four major eruptions and performed laboratory experiments at high temperatures and pressures to simulate the lava as it crystallized where it was originally stored.

They found the pools, or reservoirs, feeding the eruptions migrated from about 8 km (miles) deep in the crust during the Pompeii eruption in AD 79 to about 4 km (miles) during the Pollena eruption in AD 472.

Current technology does not allow scientists to tell where the pools are until after an eruption, which makes forecasts so important, Pichavant said.

(Reporting by Michael Kahn, Editing by Maggie Fox and Matthew Jones)