From New Scientist:
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.
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