Drilling into the Heart of a Volcano: Campi Flegrei, Southern Italy

Thurow, Juergen ¹
(1)Palaeoceanography and Sedimentology in the Department of Earth Sciences, University College of London, London, United Kingdom.

Campi Flegrei is the birthplace of myth and legend; it is also one of the most dangerous volcanoes on Earth.

Identified by the Ancients as an entrance to Hades, Campi Flegrei is a volcanic field, 12 km across, that has been the site of eruptions for at least 50,000 years. Bordering the west of Naples, in southern Italy, it is dominated structurally by a caldera, formed by collapse of the crust during the escape of 40 km³ of magma in a single eruption, 15,600 years ago. The district has since been the site of at least 56 eruptions, ranging in size from about 1-2 km³ (just smaller that the AD 79 eruption of Vesuvius, 30 km away, that destroyed Pompei and Herculaneum) to a few hundredths of a cubic kilometre. The last eruption occurred in 1538, since when the population of Campi Flegrei has grown to some 1.5 million.

In addition to eruptions, the caldera has undergone vertical movements (both uplift and subsidence) of tens of metres for at least 5,000 years. Most recently, the inner 100 km² of the district have been subject to episodes of major unrest, in 1968-72 and 1982-84, which together have produced a net maximum uplift of 3 m. The uplifts were centred about 1 km east of the old port of Pozzuoli, and ended 430 years of subsidence. In both cases, concern about an eruption triggered the evacuation of as many as 40,000 people from the Pozzuoli district.

The uplifts were produced by increases in pressure in the crust at depths of about 3 km. Because the 1538 eruption was preceded by a century of similar uplift, a major concern is that the volcano might be preparing for a new episode of volcanic activity. To investigate conditions in the zone of deformation, a 4-km borehole is scheduled to be drilled into the caldera during 2011. Sponsored by the International Continental Drilling Programme, the new borehole will complement a drilling programme for geothermal energy, conducted in the late 1970s and early 1980s by the oil company AGIP, which is now part of Italy’s state energy company ENI.

The new borehole will also be used to seek deposits from at least six explosive eruptions with volumes of several hundreds of km³ that are known to have occurred immediately north of Campi Flegrei during the past 250,000 years. Unfortunately, material from most of these super-eruptions is poorly exposed on land, so that the new borehole offers a unique opportunity to sample the deposits and to evaluate their regional impact on the environment, as well as their potential influence on global climate.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.