Environment

TO ANCIENT Romans the Phlegraean Fields hosted the entrance to Hades. In modern times it is better known as the site of a "supercolossal" volcanic eruption 39,000 years ago.

Will we see the next disaster coming? That's one of the questions an ambitious drilling project hopes to answer by sinking boreholes into Campi Flegrei, as the giant collapsed volcanic crater is now called. Starting as early as next month, the Campi Flegrei Deep Drilling Project is planning to drill seven holes in the region (see map).

Though the researchers on this particular project point out that any risk is small, it will begin amid debate about whether such endeavours are safe, given the unknowns of a volcano's interior. A few say drilling might even trigger a major eruption.

Though the caldera has no visible volcanic cone, it dwarfs nearby Vesuvius. "Most of the metropolitan area of Naples is located within the caldera," says Giuseppe De Natale of the National Institute of Geophysics and Volcanology's (INGV) Vesuvius Observatory in Naples, who is leading the project.

"A major eruption, like the one 39,000 years ago, would leave large parts of Europe buried under a thick layer of ash," says Agust Gudmundsson of the Royal Holloway University of London, one of the researchers involved in the drilling project. Since then, smaller eruptions have occurred every few centuries.

According to a study of the region by Roberto Isaia of the INGV and colleagues, Campi Flegrei is "one of the highest risk volcanic areas on Earth" and may now be primed for a blast. Isaia and colleagues found deposits from an intense period of eruptions around 4000 years ago. Before the eruptions the Earth's crust rose by several metres all across the caldera. Worryingly, crustal uplift is exactly what has happened recently. Since the late 1960s, the port of Pozzuoli near the caldera's centre has risen by around 3 metres. Hazard planners should prepare for eruptions in decades or less, Isaia concludes (Geophysical Research Letters, in press).

The drilling could reveal fracture zones and pockets of magma whose location can usually only be inferred. This could show exactly where magma might ascend and collect prior to an eruption. Meanwhile, rock samples could be tested under high stresses in the lab to help model the ground deformation prior to eruption. De Natale told New Scientist that the project - which is under the auspices of the International Continental Scientific Drilling Program and the Integrated Ocean Drilling Program - will start in December or January.

Several incidents have plagued similar projects. In June, the Iceland Deep Drilling Project (IDDP), which aims to tap geothermal energy from hot magma, had to be stopped. At 2104 metres down, magma streamed into the borehole, causing a small explosion as the drilling fluid vaporised. That project is on hold, though it will start again in 2011 with a new borehole, says Guðmundur Ómar Friðleifsson of the IDDP. And in 2005, researchers working on a drilling project in Hawaii got a fright when magma hotter than 1000 °C leaked into the borehole.

"Under unfavourable conditions, contact of the drilling fluid with magma could be very dangerous," says Ralf Büttner, a volcanologist at the University of Würzburg in Germany. "It is even theoretically conceivable that, ultimately, a major eruption could result."

Though he does not single out the Campi Flegrei project, he warns that not enough is known about what happens in the guts of a volcano to justify drilling. "Knowledge about the viscosity and processes of gases in magma is very limited." What we do know is based on extremely small samples, which makes it difficult to extrapolate the results to larger masses, he says. So volcanic drilling projects are often based on "wishful thinking rather than on hard facts", he adds.

The greatest risk would be if the drilling accidentally pierced a silica-rich magma chamber under high pressure, releasing trapped gases, saysVolker Dietrich, also of the University of Würzburg. "The threat of explosion is extremely high. Theoretically, any type of eruption could be triggered," says Dietrich. "In some circumstances, the risk is of a total disaster."

Researchers on the Campi Flegrei project accept that there are some small risks, but say prior safety assessments found that triggering a major eruption is unlikely. Christopher Kilburn of University College London, one of the lead scientists, points out that a pressure release would need to occur over a significant portion of a magma reservoir to trigger an eruption. This is "unlikely to be satisfied by a small borehole, unless, perhaps, the magma was about to erupt anyway," he explains. Bernd Zimanowski at the University of Würzburg agrees. He says that drilling into "a tough magma chamber is no different from pricking some extremely tough cookie dough".

In any case, the Campi Flegrei drilling is unlikely to hit magma. Boreholes are expected to reach a maximum depth of 4 kilometres, around half the depth of any known reservoirs, according to Jörg Erzinger of the German Research Centre for Geosciences in Potsdam (GFZ). Even if magma flows into a borehole, Ulrich Harms, another GFZ scientist, argues it would not necessarily be dangerous. "Situations like that provide exceptional insights," Harms says.

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