Massive Magma Layer Feeds Mt. Vesuvius, And May Hold Clues To Eruptions, Researchers Report In Science

Locating this reservoir won't help researchers predict exactly when the next Vesuvius eruption will take place, says Science author Paolo Gasparini of the Università di Napoli Federic II in Naples.

But, the discovery does point to a zone underneath the volcano to monitor for seismic clues, such as small earthquakes, that may signal an impending eruption, say the Science study authors.

"This also tells us that there is a huge amount of available magma under Vesuvius," says Gasparini. "It was really unexpected for the reservoir to be that size, so very wide and large. It underlies a very large area under the Neapolitan volcanoes."

Although Mt. Vesuvius' next eruption will probably be explosive, coming on the heels of a long quiet period, don't expect the magma reservoir to be drained. Most volcano experts believe that no more than 20 to 25 percent of available magma is released during any eruption, says Gasparini.

Mt. Vesuvius is relatively quiet now, trembling with mild earthquakes and venting low temperature volcanic gases in spots, but the volcano has a notable history of violent eruptions. Vesuvius is probably best known for its searing hot flows and rains of debris that buried the Roman cities of Pompeii and Herculaneum in 79 A.D.. Several significant eruptions have occurred in modern times, including the last major eruption in 1944 during World War II.

The Science researchers used a technique called seismic tomography to probe beneath Mt. Vesuvius, creating manmade explosions to generate seismic waves and tracing those waves as they travel through the crust. Data on the speed and direction of seismic waves collected by regional "listening" stations provide glimpses of the structure (and changes in structure) of the crust. Like the more familiar form of medical tomography, the CAT scan, seismic tomography combines data from these seismic station readings to build up a two- or three-dimensional picture of the crust.

Previous seismic work by the researchers, including a study published in Science (21 April 1996), hinted at a magma zone lurking beneath the volcano and the surrounding region. These experiments revealed an area of low seismic wave velocity within the crust beneath Mt. Vesuvius, where the waves were apparently slowed down and converted into different wave types.