Tuesday, September 16, 2008

Will Vesuvius' next eruption be the "big one?"

Mt. Vesuvius has been dormant for a long time. The same volcano which destroyed the towns of Herculaneum and Pompeii, but preserved much of the ruins of that city for historians to study hasn't given an indication of when it will erupt. But after over 1500 years, it is WAY past due. Some believe that, should Vesuvius erupt again, it will be the "big one." Still the people who live around Pompeii and Naples continue to go on and live their lives. Ignorance of history? Too much optimism? Who knows?

Should Naples fear a big bang from Vesuvius?
15 September 2008
NewScientist.com news service

RESIDENTS of Naples, take note: the hazard posed by Vesuvius may have to be rethought after the discovery that its magma chamber has been moving upwards towards its mouth.

Bruno Scaillet at the University of Orléans, France, and colleagues studied the proportions and types of crystal in rocks erupted from Vesuvius on four different occasions: 7800 years ago, 3600 years ago, 1929 years ago (Pompeii) and 1536 years ago. This allowed them to estimate the pressure, and hence depth, that each sample crystallised at.

By combining this with results from previous research, they were able to show that Vesuvius's magma chamber has moved upwards by between 9000 and 11,000 metres over the last 22,000 years (Nature, DOI: 10.1038/nature/07232). It isn't clear why the magma chamber has shifted, but possible reasons include changes in the shape and size of Vesuvius's mouth, a decrease in magma density, and earthquake movements.

Generally, shallower magma chambers present less of a hazard: magma at low pressure erupts less explosively. If the magma density has dropped because it contains extra water, however, it would be highly volatile, making Vesuvius go off with a bang similar to the Pompeii eruption. "No one knows what sort of magma is being stored," says Scaillet.

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