The Campi Flegrei caldera unrest: Discriminating magma intrusions from hydrothermal effects and implications for possible evolution

Abstract The Campi Flegrei caldera in Southern Italy is one of the most populated active volcanoes on Earth. It has an unprecedented record of historical unrest and eruption that dates back to 2.2 ka BP and provides key insights for understanding the dynamic evolution of large calderas. Since 1950, it has undergone four episodes of caldera-wide uplift and seismicity, which have raised the coastal town of Pozzuoli, near the centre of unrest, up to 4.5 m and triggered the repeated evacuation of some 40,000 people. After about 20 years of subsidence, following the uplift peak reached in 1984, the caldera started a new, low rate uplift episode, accompanied by low magnitude seismicity and marked geochemical changes in fumaroles. In this area it is crucial to discriminate episodes of shallow magma intrusion from hydrothermal perturbations, which are both able to generate unrest signals. In this paper, by a critical review of previous literature and some new results, we discriminate, in the unrest episodes, the relative contributions of hydrothermal effects and shallow magma intrusions. Our review is aimed also to show the different behavior of the largest unrest episodes, such as the 1982–1984, and the present, ungoing unrest characterized by smaller rate but longer lasting uplift. We show that for the former, larger uplift of the 80's, there is clear evidence for shallow magma intrusion, and we are able to compute the amount of intruded magma volume. For the present, on-going uplift, on the contrary, there is no evidence for magmatic activity at shallow depth. As a main result of our analysis, we demonstrate here the present unrest, characterized by much lower uplift rates and seismicity, is only interpretable as due to large gas fluxes coming from the deeper magma reservoir; without any appreciable contribution from shallow magma or recent magmatic intrusion. Our results shed new light on the interpretation of caldera unrest worldwide, and clearly indicate the most constraining data and the most rigorous procedures of data analysis for a correct interpretation of volcanic unrest.

[1]  G. Natale,et al.  Caldera unrest driven by CO2-induced drying of the deep hydrothermal system , 2018, Scientific Reports.

[2]  A. Nur,et al.  Ultrasonic velocity measurements in volcanic rocks: correlation with microtexture , 2002 .

[3]  Andrea Manconi,et al.  Effects of mechanical layering on volcano deformation , 2007 .

[4]  R. Esposito,et al.  Volatile Evolution of Magma Associated with the Solchiaro Eruption in the Phlegrean Volcanic District (Italy) , 2011 .

[5]  John J. Dvorak,et al.  Recent Ground Movement and Seismic Activity in Campi Flegrei , 1991 .

[6]  Claudia Troise,et al.  The ‘Campi Flegrei Deep Drilling Project’: from Risk Mitigation to Renewable Energy Production , 2011, European Review.

[7]  F. Bianco,et al.  Seismic attenuation imaging of Campi Flegrei: Evidence of gas reservoirs, hydrothermal basins, and feeding systems , 2010 .

[8]  S. Ingebritsen,et al.  Permeability of the continental crust: Implications of geothermal data and metamorphic systems , 1999 .

[9]  Renato Somma,et al.  Eruptive versus non-eruptive behaviour of large calderas: the example of Campi Flegrei caldera (southern Italy) , 2010 .

[10]  G. Chiodini,et al.  Magmas near the critical degassing pressure drive volcanic unrest towards a critical state , 2016, Nature Communications.

[11]  R. Moretti,et al.  The active portion of the Campi Flegrei caldera structure imaged by 3‐D inversion of gravity data , 2013 .

[12]  G. Giberti.  Database on laboratory measured data on physical properties of rocks of Campi Flegrei volcanic area (Italy) , 2006 .

[13]  F. Giudicepietro,et al.  A Physical Model of Sill Expansion to Explain the Dynamics of Unrest at Calderas with Application to Campi Flegrei , 2017, Front. Earth Sci..

[14]  C. Troise,et al.  The Somma-Vesuvius volcano (Southern Italy): Structure, dynamics and hazard evaluation , 2005 .

[15]  Claudia Troise,et al.  Evidence for fluid migration as the source of deformation at Campi Flegrei caldera (Italy) , 2006 .

[16]  Angioletta Coradini,et al.  Modeling of surface deformation in volcanic areas: The 1970–1972 and 1982–1984 crises of Campi Flegrei, Italy , 1987 .

[17]  G. Panza,et al.  Surface wave tomography and seismic source studies at Campi Flegrei (Italy) , 2002 .

[18]  M. Zamora,et al.  Subsurface geophysics of the Phlegrean Fields: New insights from downhole measurements , 2003 .

[19]  M. G. Di Giuseppe,et al.  Ground deformation at calderas driven by fluid injection: modelling unrest episodes at Campi Flegrei (Italy) , 2011 .

[20]  G. Panza,et al.  Magma reservoir at Mt. Vesuvius: Size of the hot, partially molten, crust material detected deeper than 8 km , 2006 .

[21]  J. Sabroux,et al.  No evidence of a new magmatic gas contribution to the Solfatara volcanic gases, during the Bradyseismic crisis at Campi Flegrei (Italy). , 1988 .

[22]  J. Gottsmann,et al.  Unrest at Campi Flegrei: A contribution to the magmatic versus hydrothermal debate from inverse and finite element modeling , 2006 .

[23]  J. Gottsmann,et al.  Faults and ground uplift at active calderas , 2006, Geological Society, London, Special Publications.

[24]  V. Morra,et al.  The Breccia Museo formation, Campi Flegrei, southern Italy: geochronology, chemostratigraphy and relationship with the Campanian Ignimbrite eruption , 2008 .

[25]  G. P. Ricciardi,et al.  Unrest episodes at Campi Flegrei: A reconstruction of vertical ground movements during 1905-2009 , 2010 .

[26]  M. Zamora,et al.  Laboratory measurements of ultrasonic wave velocities in rocks from the Campi Flegrei volcanic system and their relation to other field data , 1994 .

[27]  K. Wohletz,et al.  The thermal regime of the Campi Flegrei magmatic system reconstructed through 3D numerical simulations , 2016 .

[28]  Xu-Dong Zhu,et al.  Cyclin B-dependent kinase 1 regulates human TRF1 to modulate the resolution of sister telomeres , 2011, Nature communications.

[29]  R. T. Günther.  XXII.— The Submerged Greek and Roman Foreshore near Naples , 2022 .

[30]  L. Crescentini,et al.  Modelling deformation due to a pressurized ellipsoidal cavity, with reference to the Campi Flegrei caldera, Italy , 2011 .

[31]  Renato Somma,et al.  Tectonic stress and renewed uplift at Campi Flegrei caldera, southern Italy: New insights from caldera drilling , 2015 .

[32]  K. Pruess,et al.  TOUGH2-A General-Purpose Numerical Simulator for Multiphase Fluid and Heat Flow , 1991 .

[33]  Renato Somma,et al.  Understanding volcanic hazard at the most populated caldera in the world: Campi Flegrei, Southern Italy , 2017 .

[34]  Christopher R. J. Kilburn,et al.  Intrusion and deformation at Campi Flegrei, southern Italy: Sills, dikes, and regional extension , 2010 .

[35]  R. Moretti,et al.  The Deep Plumbing System of Ischia: a Physico-chemical Window on the Fluid-saturated and CO2-sustained Neapolitan Volcanism (Southern Italy) , 2013 .

[36]  J. Virieux,et al.  Accurate fault mechanism determinations for a 1984 earthquake swarm at Campi Flegrei caldera (Italy) during an unrest episode: Implications for volcanological research , 1995 .

[37]  G. B. Cimini,et al.  Teleseismic tomography of the Campanian volcanic area and surrounding Apenninic belt , 2001 .

[38]  Giuseppe Aiello,et al.  Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption , 2016, Scientific Reports.

[39]  G. Natale,et al.  Coulomb stress changes at calderas: Modeling the seismicity of Campi Flegrei (southern Italy) , 2003 .

[40]  P. Papale,et al.  Multiple magma degassing sources at an explosive volcano , 2013 .

[41]  G. Luongo,et al.  Inflation and microearthquake activity of phlegraean fields, Italy , 1977 .

[42]  Renato Somma,et al.  The geothermal exploration of Campanian volcanoes: Historical review and future development , 2012 .

[43]  G. Orsi,et al.  The age of the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei caldera – Italy) assessed by 40Ar/39Ar dating method , 2004 .

[44]  Mark Simons,et al.  Deformation due to a pressurized horizontal circular crack in an elastic half-space, with applications to volcano geodesy , 2001 .

[45]  Christopher G. Newhall,et al.  Historical unrest at large calderas of the world , 1989 .

[46]  R. Moretti,et al.  A CO2-rich magma source beneath the Phlegraean Volcanic District (Southern Italy): Evidence from a melt inclusion study , 2011 .

[47]  Jean Virieux,et al.  Seismic reflections reveal a massive melt layer feeding Campi Flegrei caldera , 2008 .

[48]  C. Kilburn,et al.  The volcanic and geothermally active Campi Flegrei caldera: an integrated multidisciplinary image of its buried structure , 2013, International Journal of Earth Sciences.

[49]  G. Natale,et al.  A mechanical fluid-dynamical model for ground movements at Campi Flegrei caldera , 2001 .

[50]  G. Chiodini,et al.  Monitoring and modelling hydrothermal fluid emission at La Solfatara (Phlegrean Fields, Italy). An interdisciplinary approach to the study of diffuse degassing , 2003 .

[51]  John J. Dvorak,et al.  The mechanisms of recent vertical crustal movements in Campi Flegrei caldera, southern Italy , 1991 .

[52]  Giuseppe De Natale,et al.  3-D Modelling of Campi Flegrei Ground Deformations: Role of Caldera Boundary Discontinuities , 2004 .

[53]  G. Panza,et al.  Geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings: The Tyrrhenian Sea and surroundings , 2007 .

[54]  M. Costanzo,et al.  Inferences on the lithospheric structure of Campi Flegrei District (southern Italy) from seismic noise cross-correlation , 2017 .

[55]  E. Boschi,et al.  The Campi Flegrei caldera: unrest mechanisms and hazards , 2006, Geological Society, London, Special Publications.

[56]  Riccardo Lanari,et al.  Magma injection beneath the urban area of Naples: a new mechanism for the 2012–2013 volcanic unrest at Campi Flegrei caldera , 2015, Scientific Reports.

[57]  Valerio Acocella,et al.  An overview of recent (1988 to 2014) caldera unrest: Knowledge and perspectives , 2015 .

[58]  L. Pappalardo,et al.  Rapid differentiation in a sill-like magma reservoir: a case study from the campi flegrei caldera , 2012, Scientific Reports.

[59]  P. Papale,et al.  The feeding system of Agnano-Monte Spina eruption (Campi Flegrei, Italy): Dragging the past into present activity and future scenarios , 2010 .

[60]  Frank J. Spera,et al.  Thermodynamic model for uplift and deflation episodes (bradyseism) associated with magmatic–hydrothermal activity at the Campi Flegrei (Italy) , 2009 .

[61]  G. Natale,et al.  Geophysical and geochemical modelling of the 1982 1984 unrest phenomena at Campi Flegrei caldera (southern Italy) , 1991 .

[62]  C. Oppenheimer.  Limited global change due to the largest known Quaternary eruption, Toba ≈74 kyr BP? , 2002 .

[63]  G. Natale,et al.  Understanding the Seismic Velocity Structure of Campi Flegrei Caldera (Italy): From the Laboratory to the Field Scale , 2006 .

[64]  D. Castagnolo,et al.  Genesis and evolution of unrest episodes at Campi Flegrei caldera : The role of thermal fluid-dynamical processes in the geothermal system , 1998 .

[65]  A. Zollo,et al.  The Bay of Naples (southern Italy): Constraints on the volcanic structures inferred from a dense seismic survey , 2004 .

[66]  Giuseppe De Natale,et al.  The effect of collapse structures on ground deformations in calderas , 1997 .

[67]  J. Virieux,et al.  P‐SV conversions at a shallow boundary beneath Campi Flegrei Caldera (Italy): Evidence for the magma chamber , 1992 .

[68]  M. Bonafede,et al.  Hot fluid migration in compressible saturated porous media , 1997 .

[69]  Claudia Troise,et al.  A geochemical and geophysical reappraisal to the significance of the recent unrest at Campi Flegrei caldera (Southern Italy) , 2017 .

[70]  John B. Rundle,et al.  Ground deformation in a viscoelastic medium composed of a layer overlying a half-space: a comparison between point and extended sources , 2000 .

[71]  C. Morhange,et al.  New data on historical relative sea level movements in Pozzuoli, phlaegrean fields, Southern Italy , 1999 .

[72]  Harvey E. Belkin,et al.  Quantitative model for magma degassing and ground deformation (bradyseism) at Campi Flegrei, Italy: Implications for future eruptions , 2007 .

[73]  Luca D'Auria,et al.  Evidence of thermal-driven processes triggering the 2005–2014 unrest at Campi Flegrei caldera , 2015 .

[74]  Christophe Morhange,et al.  Rapid sea-level movements and noneruptive crustal deformations in the Phlegrean Fields caldera, Italy , 2006 .

[75]  J. Virieux,et al.  Seismic Evidence for a Low-Velocity Zone in the Upper Crust Beneath Mount Vesuvius , 1996, Science.

[76]  Renato Somma,et al.  The Campi Flegrei Deep Drilling Project (CFDDP): New insight on caldera structure, evolution and hazard implications for the Naples area (Southern Italy) , 2016 .

[77]  G. Chiodini,et al.  Magma degassing as a trigger of bradyseismic events: The case of Phlegrean Fields (Italy) , 2003 .

[78]  Enzo Boschi,et al.  Renewed ground uplift at Campi Flegrei caldera (Italy): New insight on magmatic processes and forecast , 2007 .

[79]  C. Kilburn,et al.  Progressive approach to eruption at Campi Flegrei caldera in southern Italy , 2017, Nature Communications.

[80]  F. Innocenti,et al.  Phlegraean Fields 1982–1984: Brief chronicle of a volcano emergency in a densely populated area , 1984 .

[81]  Warner Marzocchi,et al.  Probabilistic eruption forecasting at short and long time scales , 2012, Bulletin of Volcanology.

[82]  Carlo Cardellini,et al.  First observations of the fumarolic gas output from a restless caldera: Implications for the current period of unrest (2005–2013) at Campi Flegrei , 2013 .

[83]  J. Gilluly,et al.  Principles of Geology , 1969 .

[84]  I. Arienzo,et al.  Experimental determination of permeability of Neapolitan Yellow Tuff , 2007 .

[85]  D. Marsan,et al.  Clues on the origin of post-2000 earthquakes at Campi Flegrei caldera (Italy) , 2017, Scientific Reports.

[86]  S. Carlino,et al.  Caldera subsidence in extensional tectonics , 2014, Bulletin of Volcanology.

[87]  J. Virieux,et al.  Merging active and passive data sets in traveltime tomography: The case study of Campi Flegrei caldera (Southern Italy) , 2008 .

[88]  P. Papale,et al.  The deep magmatic system of the Campi Flegrei caldera (Italy) , 2008 .

[89]  Indyo Pratomo,et al.  Resurgent Toba—field, chronologic, and model constraints on time scales and mechanisms of resurgence at large calderas , 2015, Front. Earth Sci..

[90]  Giovanna Berrino,et al.  Ground deformation and gravity changes accompanying the 1982 Pozzuoli uplift , 1984 .

[91]  P. Petrosino,et al.  Research progress in volcanology in the Neapolitan area, southern Italy: a review and some alternative views , 2010 .

[92]  Rosario Avino,et al.  The origin of the fumaroles of La Solfatara (Campi Flegrei, South Italy) , 2007 .

[93]  G. Panza,et al.  Chapter 6 Shear-wave velocity models and seismic sources in campanian volcanic areas: Vesuvius and phlegraean fields , 2006 .

[94]  D. Castagnolo,et al.  A physical appraisal of a new aspect of bradyseism: The miniuplifts , 2003 .

[95]  F. Giudicepietro,et al.  Sill intrusion as a source mechanism of unrest at volcanic calderas , 2014 .

[96]  Aldo Zollo,et al.  Statistical analysis and clustering features of the Phlegraean Fields earthquake sequence (May 1983-May 1984) , 1986 .

[97]  W. Marzocchi,et al.  Operational eruption forecasting at high-risk volcanoes: the case of Campi Flegrei, Naples , 2012, Journal of Applied Volcanology.

[98]  G. Berrino,et al.  On deformation sources in volcanic areas: modeling the Campi Flegrei (Italy) 1982-84 unrest , 2011 .

[99]  L. Casertano,et al.  Hydrodynamics and geodynamics in the Phlegraean fields area of Italy , 1976, Nature.