Paired deformation sources of the Campi Flegrei caldera (Italy) required by recent (1980-2010) deformation history

Abstract

We analyze 1980–2010 ground displacements, to discern similarities or differences between Campi Flegrei (CF) inflations and deflations and highlight possible anomalies in particular areas. We show that the deformation pattern can be decomposed into two stationary (constant over time, except for a mere scaling factor) parts; both of them are satisfied by simple deformation sources. A quasi-horizontal elongated crack (oriented NW to SE, and embedded in an elastic layered half-space at a depth of about 3600 m) satisfies large-scale deformation. All source parameters but potency (volume change) are constant over time. Residual deformation is confined to the area of the Solfatara fumarolic field and satisfied by a small spheroid located at about 1900 m in depth. Again, all source parameters but potency are constant over time. The histories of the two sources are somewhat similar but not equal, supporting the existence of a genuine local deformation source at Solfatara against the emergence of a mere distortion of large-scale deformation. Although reality is probably much more complex, our simple model explains 1980–2010 CF deformation within ground-displacement data errors and is consistent with Solfatara geochemical conceptual models, fumarolic geochemical data, and seismic attenuation imaging of CF. The observation that the CF deformation pattern can be decomposed into two stationary parts is hardly compatible with several recent works which proposed multiple sources with different features acting in different periods, fluid injections implying ample changes of large-scale deformation pattern over time, complex spatio-temporal patterns of distributions of volumetric sources

Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

“…4), the location and depth of the 1400–1536 source, below the caldera centre, are consistent with the source (defined by the inversion of geodetic data) responsible for most of the surface deformation since 19801213 and the previous unrest episodes26. The caldera centre also coincides with the maximum uplift of the resurgence (Fig.…”

“…5), where magma propagation appears controlled by two processes:

The formation of sills along subhorizontal discontinuities below the caldera; geological, geophysical and modelling data show how the stresses focus at the tips of the sills, which propagate laterally, fracturing and intruding the host rock35 [references therein]. Analysis of historical and satellite geodetic data indicates the existence of a sill-like source at a depth of ~4 km that may explain the caldera deformation12.

The stresses promoted by the caldera unloading, expressed by the topographic (usually >100 m for Campi Flegrei), bathymetric (>50 m on average) and density (of 0.2–0.4 g/cm 3 ; ref. 3) variations between the caldera centre and periphery36; these stresses are characterized by the progressive rotation of the minimum compression direction from sub-vertical below the caldera to sub-horizontal at the sides, as schematized in Fig.…”

“…These unrest episodes are considered the most evident expression of a longer-term (centuries or more) restless activity410. The post-1980 deformation largely results from a magmatic oblate or sill-like source at ~4 km depth below Pozzuoli (e.g 12. and references therein13); however, an important role for the hydrothermal system has been also proposed14 [references therein].…”

Isotopic microanalysis sheds light on the magmatic endmembers feeding volcanic eruptions: The Astroni 6 case study (Campi Flegrei, Italy)

“…Should the fresh magma be hot and gas-rich, it might cause re-melting of a crystal mush, an event that possibly occurred in the past at Ischia (Brown et al, 2014) as well as in other volcanoes (e.g., Burgisser and Bergantz, 2011;Wiesmaier et al, 2012). There are several geophysical lines of evidence suggesting that the most intense, recent unrest event that occurred at Campi Flegrei (1982)(1983)(1984) might have been caused by the emplacement at shallow depth of a small volume of magma, on the order of 0.01 km 3 (e.g., De Siena et al, 2010;Trasatti et al, 2011;Amoruso et al, 2014). Since that episode has not been followed by an eruption, it is very likely that today, after more than 30 years, that small magma batch is almost, if not completely crystallized (K. Wohletz, pers.…”

Recognizing and tracking volcanic hazards related to non-magmatic unrest: a review

“…The discussion as to whether the unrest at Campi Flegrei since the 1980's is magmatic (Bianchi et al 1987;Bonafede et al 1986;Gottsmann et al 2006), or non-magmatic (Casertano et al 1976;Bonafede 1991;De Natale et al 1991;Gaeta et al 1998) is still ongoing. Recently, the tendency to explain the uplift by the expansion of the underlying hydrothermal system has become more plausible as it is supported by decade-long monitoring time series (geochemistry, geodesy, geophysical surveys) (Chiodini et al 2001Todesco et al 2003), even though the deformation pattern may be explained by alternative models (e.g., Amoruso et al 2014). The Campi Flegrei unrest, causing major concern also because the caldera is highly populated, is an example of prolonged hydrothermal noneruptive unrest manifested as ground deformation paired with diffuse degassing.…”