Note Press
Rome, 6 December 2016
A stratigraphic study in the well of the Campi Flegrei Deep Drilling Project (CFDDP) has allowed us to reconstruct the evolution of the eruptive activity in the eastern sector of the Campi Flegrei, which took place in sometimes sub-aerial and sometimes submarine environments, up to about 47.000 years ago. This is what emerges from the first results on the study of the stratigraphy of the Bagnoli well carried out by the Vesuvius Observatory of the National Institute of Geophysics and Volcanology (OV-INGV), published in the journal 'Geochemistry, Geophysics, Geosystems' of the American Geophysical Union.
The article (http://onlinelibrary.wiley.com/doi/10.1002/2015GC006183/full), entitled 'The Campi Flegrei Deep Drilling Project (CFDDP): New insight on caldera structure, evolution and hazard implications for the Naples area (Southern Italy)', describes the complete stratigraphy of the well (501 meters deep and located in Bagnoli at close to the Posillipo hill) and the analyzes carried out on the campsextracted rock ions, in particular absolute dating with radioactive methods.
"This stratigraphic study", explains Giuseppe De Natale, OV-INGV research manager and project coordinator, "has made it possible to reconstruct, over time, the evolution of the eruptive activity in this sector of the caldera, up to around 47.000 years ago . The most important information was obtained from the discovery in the well of the products of the two main eruptions which are thought to have formed the caldera: the Campanian Ignimbrite, from 39.000 years ago, and the Yellow Neapolitan Tuff, from 15.000 years ago”.
The stratigraphic position of the products of these two super-eruptions, the considerable superficiality at which they were found and their limited thickness, place strong constraints on the definition of the limits of the caldera and on the mechanisms which have determined both its collapse during the more explosive eruptions and the large slow deformations of the soil during its long dynamics. The caldera is in fact home to slow deformations of the ground, the so-called "bradyseism", well known for recent times. The study of rock sequences in drilling also allows us to investigate the oldest soil dynamics.
In particular, adds De Natale, "while until now almost all of the scientific literature hypothesized that the Campanian Ignimbrite caldera also contained the central part of the city of Naples, the new data clearly indicate that the hill of Posillipo represents the eastern limit of the Phlegrean Caldera, both for the Neapolitan Yellow Tuff and for the Campanian Ignimbrite. The identification of Posillipo as the eastern limit of the caldera for all collapse eruptions represents a very important indication for correctly determining the volcanic hazard in the city centre. Furthermore, the notable superficiality of the eruptive products of even very ancient eruptions implies that, in the eastern sector of the caldera, the volume of eruptive products is much smaller than what happens in the western sector, thus generically highlighting a lower impact of the eruptions in the eastern sector, in the last 47.000 years.”
"These important new information on the evolution, the eruptive history and the structural limits of the eastern part of the caldera also allow a substantial re-evaluation of the volcanic hazard and of the eruptive scenarios themselves for the city of Naples", concludes De Natale.
Reconstruction of the limits of the Flegrea caldera. The thick yellow line and the purple shaded area, at the Posillipo hill, represent the boundary of the Neapolitan Yellow Tufo and Campanian Ignimbrite caldera, respectively, as obtained in this study.
Extended
The 501m-deep hole of the Campi Flegrei Deep Drilling Project, located west of the Naples metropolitan area and inside the Campi Flegrei caldera, gives new insight to reconstruct the volcano-tectonic evolution of this highly populated volcano. It is one of the highest risk volcanic areas in the world, but its tectonic structure, eruptive history and size of the largest eruptions are intensely debated in literature. New stratigraphic and 40Ar/39Ar geochronological dating allow us to determine, for the first time, the age of intra-caldera deposits belonging to the two highest magnitude caldera-forming eruptions (ie Campanian Ignimbrite, CI, 39 ka, and Neapolitan Yellow Tuff, NYT, 14.9 ka) and to estimate the amount of collapse. Tuffs from 439 m of depth yield the first 40Ar/39Ar age of c. 39 ka within the caldera, consistent with the CI. Volcanic rocks from the NYT were, more over, detected between 250 m and 160 m. Our findings highlight: i) a reduction of
the area affected by caldera collapses, which appears to not include the city of Naples; ii) a small volume of the infilling caldera deposits, particularly for the CI and iii) the need for reassessment of the collapse amounts and mechanisms related to larger 27 eruptions. Our results also imply a revaluation of volcanic risk for the eastern caldera area, including the city of Naples. The results of this study point out that large calderas are characterized by complex collapse mechanisms and dynamics, whose understanding needs more robust constraints, which can be obtained from scientific drilling.
Authors: De Natale, G., Troise, C., Mark, D., Mormone, A., Piochi, M., Di Vito, MA, Isaia, R., Carlino, S., Barra, D., Somma, R. The Campi Flegrei Deep Drilling Project (CFDDP) - New insight on caldera structure, evolution and hazard implications for the Naples area (Southern Italy). Geochemistry, Geophysics, Geosystems, AGU, 2016.
For further information: Giuseppe De Natale INGV-OV, e-mail: