What Lies Beneath is What We Cannot Fathom

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Bill mcGuire considers whether we should be toying with what lies beneath. During prehistoric times, cataclysmic eruptions at one or other of the world’s supervolcanoes devastated huge tracts of our planet and, on one occasion, may even have brought the human race to the brink of extinction. It is more than 25,000 years since the last titanic explosion at a super volcano – in Taupo, New Zealand – so modern society has never had to face the trauma of a volcanic cataclysm with the potential to trigger a global freeze and worldwide harvest failure.

But the threat remains ever-present. You might think, therefore, that drilling into one of these monstrous volcanoes is probably not a good idea. This, however, is exactly what a European consortium of scientists is about to do in southern Italy. Opposition from many citizens and local politicians, who fear that the drilling may trigger an eruption, has resulted in repeated delays to the project.

Now, though, scientists appear to have allayed these fears as much as they can, so all is set for a borehole to slice 3.8km (2.4miles) down into the Campi Flegrei super volcano near Naples later this summer.

Campi Flegrei is not the volcano that everyone associates with the city of Naples. Whenever the ground has rumbled in the past, the eyes of its residents have inevitably turned eastwards towards the brooding double peak of Vesuvius, rather than to the west, where Campi Flegrei sits. This all changed in the late 1960s and early 1970s, when swarms of earthquakes and the bulging upwards of the crust resulted in the giant volcanic crater joining the ranks of the so-called ‘restless’ calderas, others of which include Yellowstone in Wyoming and the Greek island volcano, Santorini. There is still plenty that we don’t know about supervolcanoes.

Volcanologists have speculated that the reason magma is often released in one massive burp rather than in dribs and drabs is because the crust above swells and stretches, opening up fractures that slice down from the surface, instantaneously creating a conduit. Given such a scenario, it remains uncertain, however, what warning signs – if any – might be seen before a super-eruption, or how soon in advance they would become apparent. We also can’t determine whether an episode of unrest will die down again or culminate in a volcanic blast of unimaginable proportions.

One such unsettled period provided a frisson of excitement for the population of the north-west US, when swelling of the Yellowstone supervolcano, which started in 2004, was accompanied in 2009 and 2010 by thousands of small earthquakes, suggesting that magma was on the move. To everyone’s relief, unrest at Yellowstone has subsided – at least for the moment. However, one day, somewhere – maybe at Yellowstone itself, at Toba in Sumatra, or at Bolivia’s remorselessly swelling volcano, Uturuncu – such rumblings will translate into an eruption. So we need to learn now how to recognise the tell-tale signs that will give us sufficient warning.

It is hoped that the drilling campaign at Campi Flegrei will help to do this by allowing researchers to build a detailed picture of a supervolcano’s innards. Sensors lowered down the borehole will provide measurements on the mechanical properties of the volcanic rock, including permeability and temperature, as well as monitoring future changes in those properties that might herald an eruption. Extracted samples will also enable the hidden products of past eruptions to be catalogued. Although Campi Flegrei’s last eruption, in 1538, was pretty small, its greatest prehistoric blasts were titanic. Today, such an event could threaten the lives and livelihoods of several million people.

With this in mind then, should volcanologists be taking the risk of poking this sleeping giant? Could their interference actually provoke an eruption? There is precedent for magma coming up a borehole. In Iceland in 1979, magma moving deep underground encountered a kilometre-deep borehole drilled to tap geothermal energy. Around three tonnes of fluid basalt spluttered out of the top of the hole before the magma congealed and blocked the conduit. The magma lurking below Campi Flegrei, though, is much stickier and deeper down, so the chances of any managing to squeeze up a thin tube nearly 4km (2.5miles) long to reach the surface are vanishingly small. In short, drilling into a supervolcano is a bit like sticking a drawing pin into an elephant’s bottom and can be expected to have a similar effect – none at all. There’s a very good chance that Campi Flegrei will host another cataclysmic eruption, but not this year.

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