Report on Campi Flegrei (Italy) — September 1984

Scientific Event Alert Network Bulletin, vol. 9, no. 9 (September 1984)
Managing Editor: Lindsay McClelland.

Campi Flegrei (Italy) More M > 3 events with wider distribution, but seismic energy release unchanged and uplift slows

Please cite this report as:

Global Volcanism Program, 1984. Report on Campi Flegrei (Italy). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 9:9. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.SEAN198409-211010.

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Campi Flegrei

Italy

40.827°N, 14.139°E; summit elev. 458 m

All times are local (unless otherwise noted)


"Activity at Campi Flegrei displayed some changes July-September. The monthly mean uplift velocity was in the range of 1.2 mm/day at Pozzuoli and <1 mm/day at Nisida. A new tide gauge is now operating on the W side of the caldera near Cape Miseno. The mean velocity of uplift in that area is comparable to that at Nisida. The velocity of uplift during the last 3 months is lower than that during the winter and spring.

"Seismic energy release remained at the same level as in the past year. We observed a higher number of the most energetic events (M 3) than in past months (table 1). They are also no longer confined within the restricted area around Solfatara Crater, but instead occur all over the seismically active area.

Table 1. Magnitudes of the most energetic events in the Campi Flegrei area, July-September 1984.

[Skip text table]
    Date        Magnitude

    01 Jul 84   3.7, 3.5
    11 Jul 84   3.8
    22 Aug 84   3.6
    29 Aug 84   3.9, 3.8
    12 Sep 84   3.3
    13 Sep 84   3.2
    28 Sep 84   3.5, 3.7

"The temperatures of fumaroles in Solfatara Crater remained stable. The radon content of the water wells reached a minimum in the last year, with a slight increase again at the end of September.

"The decrease in the uplift velocity during constant seismic energy release does not support the idea that uplift velocity is closely related to the occurrence of larger earthquakes. On the contrary, in this last period we have observed higher-energy events. They often occur as double events (1 July, 29 August and 28 September; table 1). The area that was previously affected by swarms of low-energy events (1 km W of Pozzuoli) is now also affected by high-energy events. We do not know if this pattern of activity indicates a higher risk of eruption."

Geologic Background. Campi Flegrei is a large 13-km-wide caldera on the outskirts of Naples that contains numerous phreatic tuff rings and pyroclastic cones. The caldera margins are poorly defined, and on the south lie beneath the Gulf of Pozzuoli. Episodes of dramatic uplift and subsidence within the dominantly trachytic caldera have occurred since Roman times. The earliest known eruptive products are dated 47,000 yrs BP. The caldera formed following two large explosive eruptions, the massive Campanian ignimbrite about 36,000 BP, and the >40 cu km Neapolitan Yellow Tuff (NYT) about 15,000 BP. Following eruption of the NYT a large number of eruptions have taken place from widely scattered subaerial and submarine vents. Most activity occurred during three intervals: 15,000-9500, 8600-8200, and 4800-3800 BP. Two eruptions have occurred in historical time, one in 1158 at Solfatara and the other in 1538 that formed the Monte Nuovo cinder cone.

Information Contacts: G. Luongo and R. Scandone, OV; F. Barberi, Univ. di Pisa.