Invited research article
Post-collapse evolution of a coastal caldera system: Insights from a 3D multichannel seismic survey from the Campi Flegrei caldera (Italy)

https://doi.org/10.1016/j.jvolgeores.2017.09.023Get rights and content

Highlights

  • First 3D reflection seismic investigation of a (partly) submerged caldera setting.

  • Inner caldera ring-fault consists of four linear fault segments.

  • Caldera faults have acted as pathway for fluid ascent and intrusion emplacement.

  • Offshore caldera portion may be of significant importance for the degassing budget.

  • Post-collapse eruption volumes may be underestimated by 3 to 4 times.

Abstract

In this study we present the first 3D high-resolution multichannel seismic dataset from a (partly) submerged caldera setting, the Campi Flegrei caldera (CFc). Our work aims at examining the spatial and temporal evolution of the CFc since the last caldera-forming event, the Neapolitan Yellow Tuff (NYT, 15 ka) eruption. The main objectives are to investigate the caldera's shallow (< 200 m) subsurface structure and post-NYT-collapse (< 15 ka) deformational processes, the manifestation of magmatic and hydrothermal processes in the subsurface, as well as the volume, dispersal and explosivity of coastal post-collapse eruptions, thereby significantly advancing our current knowledge of the CFc.

Our findings confirm the existence of a nested-caldera system comprising two caldera depressions bordered by an inner and a deeper (> 200 m) outer caldera ring-fault zone. The seismic data revealed that the NYT collapse occurred exclusively along the inner caldera ring-fault and that the related NYT caldera depression is filled with on average ~ 61 m of sediment deposited between 15 and 8.6 ka. The geometry of the inner ring-fault, consisting of four fault segments, seems to be strongly influenced by regional NW-SE and NE SW-trending faults. Furthermore, we found that the ring-faults have acted as pathway for the recent (< 3.7 ka) ascent of fluids (gases and liquids) and the emplacement of intrusions. We propose that the outer ring-fault zone, which likely formed in the course of the Campanian Ignimbrite (CI, 39 ka) eruption, has had the main control on the release and ascent of fluids. Overall, the caldera ring-faults represent key locations for the interconnection between the magmatic-hydrothermal systems and the surface and, thus, potentially represent future eruption sites as well as important fluid pathways during the recent unrest episodes.

Furthermore, we reassessed the volume, dispersal, and explosivity of the post-collapse Nisida Bank (10.3–9.5 ka), Nisida Island (~ 3.98 ka), and Capo Miseno (3.7 ka) eruptions, yielding DRE values of 0.15 km3, 0.1 km3, and 0.08 km3, respectively, and an explosive magnitude of at least moderate-large scale (VEI 3). Our findings highlight that eruption volumes may be underestimated by 3 to 4 times if the submerged portion of a (partly) submerged caldera is not considered, implying severe consequences for the hazard and risk evaluation.

The spatial response of the post-collapse (< 15 ka) depositional environment to volcanic activity, deformational processes and sea-level variations is presented in a comprehensive 3D evolutionary model.

Introduction

Caldera-forming explosive eruptions are considered as one of the most catastrophic natural event to affect the Earth's surface and human society (Rampino, 2002, Self, 2015). Also in their post-collapse phase, a large number of calderas remain active as evident by caldera resurgence (Smith and Bailey, 1968, Acocella et al., 2001, Cole et al., 2005), short-term episodes of unrest involving seismicity, ground deformation, and hydrothermal activity (Newhall and Dzurisin, 1988, Acocella et al., 2015), as well as volcanic intrusions and eruptions (Cole et al., 2005). Such active calderas pose high concern for imminent volcanic activity. Major structural features such as caldera ring-faults or regional tectonic fractures represent preferential magma ascent pathways (Moore and Kokelaar, 1997, Saunders, 2004), thereby depicting potential post-collapse eruption sites. Hence, the acquisition of veridical information on the structural framework of calderas is crucial to be able to assess the location and timing of future eruptions. Moreover, understanding the past volcanic eruption history, including the areal distribution and volumes of products from former eruptions, is essential for a reliable hazard and risk assessment. However, to fully comprehend such a staggeringly complex system, a detailed 3D investigation of the subsurface is indispensable.

The partly submerged Campi Flegrei caldera (CFc), located in southern Italy, represents one of the world's most active calderas (De Natale et al., 2006, Del Gaudio et al., 2010) and, thus, provides an ideal natural laboratory to study post-collapse evolutionary processes at an active caldera. Generally, the CFc is regarded as nested-caldera system formed by two major eruptions namely the Campanian Ignimbrite (CI) and the Neapolitan Yellow Tuff (NYT) eruptions at 39 and 15 ka, respectively (e.g. Rosi et al., 1983, Barberi et al., 1991, Orsi et al., 1996, Deino et al., 2004). Since the last caldera-forming event related to the NYT eruption, the CFc has been modified by various post-collapse processes including long-term caldera resurgence (Orsi et al., 1996, Acocella, 2010), ~ 60 volcanic eruptions (Di Vito et al., 1999), sea-level variations (D'Argenio et al., 2004b, Steinmann et al., 2016), as well as recent unrest since the 1950s (Del Gaudio et al., 2010, Chiodini et al., 2012). In particular, the linkage between the magmatic and hydrothermal systems as well as their contribution to the recent unrest episode remain a matter of discussion, thereby impairing a reliable evaluation of the eruption potential and assessment of volcanic risks (e.g. Lima et al., 2009, D'Auria et al., 2015, Chiodini et al., 2016). A detailed 3D understanding of the CFc architecture in particular – but also of calderas in general – is scarce in the current literature; however, essential for unravelling the interconnection between the deep magmatic-hydrothermal systems and the surface as well as potential eruption pathways. In fact, the caldera's subsurface structure including the location of the main caldera ring-faults – in particular their offshore continuation – remains debated and inhomogeneous (Orsi et al., 1996, Bellucci et al., 2006, Perrotta et al., 2006, Acocella, 2008, Vitale and Isaia, 2014, De Natale et al., 2016). Even though, the approximate offshore extent of the caldera margin could be circumscribed (Fig. 1) based on geophysical studies including seismic refraction tomography (e.g. Zollo et al., 2003, Judenherc and Zollo, 2004, Dello Iacono et al., 2009), gravity (e.g. Florio et al., 1999, Capuano and Achauer, 2003, Capuano et al., 2013) and magnetic (e.g. Florio et al., 1999, Secomandi et al., 2003, Aiello et al., 2005) measurements, interpretational uncertainties remained due to the dataset's low resolution and, thus, lack of structural detail. More detailed insights into the shallow structures of the submerged CFc were provided by high-frequency 2D marine reflection seismic investigations (D'Argenio et al., 2004b, Milia, 2010, Aiello et al., 2012, Sacchi et al., 2014, Steinmann et al., 2016). These reflection seismic studies stand out due to their high-resolution, however, they lacked spatial coverage, which is crucial in order to fully comprehend a complex caldera system. Moreover, the volume and dispersal of post-collapse volcanic eruptions of the CFc is still controversial and mainly based on onshore field observations and/or borehole data (e.g. Rosi et al., 1983, Orsi et al., 1996, Di Vito et al., 1999), thereby providing only selective insights and neglecting the marine portion, which represents approximately half of the entire caldera structure.

In this study we present a 3D grid of high-resolution multichannel seismic data (Fig. 1B) from the submerged sector of the CFc, providing an ideal combination of high vertical resolution (~ 2 m) and good spatial coverage and, thus, the best means to obtain 3D information on the caldera system. This marine dataset enables a detailed spatial investigation of the structural and stratigraphic framework down to a subsurface depth of 200 m without the challenges posed on land by intense subaerial erosion or urbanization (i.e. inaccessibility). The main aims of this 3D–investigation are to examine the caldera's subsurface structure and post-collapse (< 15 ka) deformational processes, the impact of hydrothermalism and magmatism (e.g. intrusions) on the offshore sector of the caldera, as well as to reassess the volume, dispersal and explosivity of coastal post-caldera eruption. The here presented work complements a previous study from Steinmann et al. (2016), which focused on a conceptual reconstruction of the caldera formation since CI eruption at 39 ka based on five selected seismic lines from the presented 3D grid. While the preceding study addressed fundamental aspects regarding the structural evolution (collapse, resurgence) of the CFc in interplay with sea-level changes in the 2D domain, the here presented work aims at providing detailed, 3D–insights on the shallow caldera structure and post-collapse processes (hydrothermalism, magmatism, volcanic activity, deformation). Moreover, the previously established stratigraphic and structural framework (e.g. seismic units, inner caldera ring-fault, and resurgent dome) could be spatially extended over the entire marine portion of the CFc and a higher stratigraphic resolution in the uppermost interval was achieved.

Section snippets

Regional setting

The CFc is a Quaternary caldera located within the graben-like structure of the Campanian Plain (southern Italy) between the Tyrrhenian Sea and Apenninic Mountain range (Fig. 1A). It is situated in a densely populated region with the city of Naples at its eastern border and the town of Pozzuoli in its centre (Fig. 1C). As proven by recent episodes of unrest, the Campi Flegrei district represents one of the world's most active calderas (Troise et al., 2008). With 360,000 people living within the

Material and methods

Here we present a grid of high-resolution multichannel seismic profiles collected during an oceanographic cruise (CAFE-7/3) on the R/V URANIA in the Gulf of Naples and the Gulf of Pozzuoli in 2008 (Fig. 1B). This study is based on in total 88 seismic profiles of which 48 are part of a densely spaced (75–150 m spacing) N-S oriented grid crossing over the offshore sector of the CFc. Data acquisition was carried out using the high-resolution multichannel seismic system of the Faculty of Geosciences

Results

For the sake of clarity, we use the same nomenclature for the seismic units as established in the preceding study by Steinmann et al. (2016). In total, we refer to four previously identified marine sedimentary units (M1–M4) and two volcaniclastic units (NYT, V2) with four associated unconformities (U1–U4) as well as major structural features such as the inner caldera ring-fault and a resurgent dome with an apical fault swarm. The sedimentary deposits likely consist to some extent of reworked

Discussion

The focus of this study lies on post-NYT-collapse (< 15 ka) caldera processes, hence, the seismostratigraphic interpretation addresses mainly the corresponding units (M2–M4.2, V2–V4). A summary of volcanic activity, sea-level variations and deformational processes in context of the established seismostratigraphy is provided in Fig. 7. For a more detailed analysis of the depositional environment prior the NYT eruption as well as caldera-forming processes associated with the CI and NYT eruptions,

Conclusions

In this study, we presented the first 3D high-resolution multichannel seismic dataset from a partly submerged caldera setting. Our investigation of the marine portion of the Campi Flegrei caldera (CFc) provided novel insights into the caldera's shallow (< 200 m) subsurface structure and post-collapse (< 15 ka) deformational processes, the manifestation of magmatic and hydrothermal processes in the shallow subsurface, as well as the volume, dispersal and explosivity of coastal post-collapse

Acknowledgements

The seismic dataset was acquired during the CAFE-7/3 expedition funded by the Italian Research Council through the CNR Shiptime Programme (Oceanographic Cruise_CAFE_07), seismic acquisition was supported by German Research Foundation (DFG) within the ICDP priority programme (Grant No. SP296/30-1). Data processing and analysis was funded through the DFG's ICDP priority programme (Grant No. SP296/34-1; SP296/34-2). Additional support was provided by the Bremen International Graduate School for

References (85)

  • A.L. Deino et al.

    The age of the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei caldera – Italy) assessed by 40Ar/39Ar dating method

    J. Volcanol. Geotherm. Res.

    (2004)
  • C. Del Gaudio et al.

    Unrest episodes at Campi Flegrei: a reconstruction of vertical ground movements during 1905–2009

    J. Volcanol. Geotherm. Res.

    (2010)
  • V. Di Renzo et al.

    The magmatic feeding system of the Campi Flegrei caldera: architecture and temporal evolution

    Chem. Geol.

    (2011)
  • M.A. Di Vito et al.

    Volcanism and deformation since 12,000 years at the Campi Flegrei caldera (Italy)

    J. Volcanol. Geotherm. Res.

    (1999)
  • T.P. Fischer et al.

    Volcanic, Magmatic and Hydrothermal Gases A2 - Sigurdsson, Haraldur, The Encyclopedia of Volcanoes

    (2015)
  • G. Florio et al.

    The Campanian Plain and Phlegrean Fields: structural setting from potential field data

    J. Volcanol. Geotherm. Res.

    (1999)
  • D. Insinga et al.

    The Late-Holocene evolution of the Miseno area (south-western Campi Flegrei) as inferred by stratigraphy, petrochemistry and 40Ar/39Ar geochronology

  • A. Jasim et al.

    Impact of channelized flow on temperature distribution and fluid flow in restless calderas: insight from Campi Flegrei caldera, Italy

    J. Volcanol. Geotherm. Res.

    (2015)
  • K. Lambeck et al.

    Sea level change along the Italian coast during the Holocene and projections for the future

    Quat. Int.

    (2011)
  • A. Lima et al.

    Thermodynamic model for uplift and deflation episodes (bradyseism) associated with magmatic–hydrothermal activity at the Campi Flegrei (Italy)

    Earth Sci. Rev.

    (2009)
  • D. Mele et al.

    Hazard of pyroclastic density currents at the Campi Flegrei Caldera (Southern Italy) as deduced from the combined use of facies architecture, physical modeling and statistics of the impact parameters

    J. Volcanol. Geotherm. Res.

    (2015)
  • G. Orsi et al.

    The restless, resurgent Campi Flegrei nested caldera (Italy): constraints on its evolution and configuration

    J. Volcanol. Geotherm. Res.

    (1996)
  • S. Passaro et al.

    Multi-resolution morpho-bathymetric survey results at the Pozzuoli–Baia underwater archaeological site (Naples, Italy)

    J. Archaeol. Sci.

    (2013)
  • A. Perrotta et al.

    The Campi Flegrei caldera boundary in the city of Naples

    Develop. Volcanol.

    (2006)
  • M. Poland et al.

    Constraints on the mechanism of long-term, steady subsidence at Medicine Lake volcano, northern California, from GPS, leveling, and InSAR

    J. Volcanol. Geotherm. Res.

    (2006)
  • M.R. Rampino

    Supereruptions as a threat to civilizations on earth-like planets

    Icarus

    (2002)
  • M. Rosi et al.

    The phlegraean fields: structural evolution, volcanic history and eruptive mechanisms

    J. Volcanol. Geotherm. Res.

    (1983)
  • S. Rossano et al.

    Numerical simulation of pyroclastic density currents on Campi Flegrei topography: a tool for statistical hazard estimation

    J. Volcanol. Geotherm. Res.

    (2004)
  • M. Sacchi et al.

    The Neapolitan Yellow Tuff caldera offshore the Campi Flegrei: stratal architecture and kinematic reconstruction during the last 15 ky

    Mar. Geol.

    (2014)
  • S. Self

    Explosive super-eruptions and potential global impacts

  • L. Steinmann et al.

    The Campi Flegrei caldera (Italy): formation and evolution in interplay with sea-level variations since the Campanian Ignimbrite eruption at 39 ka

    J. Volcanol. Geotherm. Res.

    (2016)
  • C. Troise et al.

    A new uplift episode at Campi Flegrei Caldera (Southern Italy): implications for unrest interpretation and eruption hazard

    Evaluation

    (2008)
  • K. Wohletz et al.

    Thermal evolution of the Phlegraean magmatic system

    J. Volcanol. Geotherm. Res.

    (1999)
  • V. Acocella

    Activating and reactivating pairs of nested collapses during caldera-forming eruptions: Campi Flegrei (Italy)

    Geophys. Res. Lett.

    (2008)
  • V. Acocella

    Evaluating fracture patterns within a resurgent caldera: Campi Flegrei, Italy

    Bull. Volcanol.

    (2010)
  • V. Acocella et al.

    An overview of recent (1988 to 2014) caldera unrest: knowledge and perspectives

    Rev. Geophys.

    (2015)
  • G. Aiello et al.

    Buried Volcanic Structures in the Gulf of Naples (Southern Tyrrhenian Sea, Italy) Resulting From High Resolution Magnetic Survey and Seismic Profiling

    (2005)
  • G. Aiello et al.

    New seismo-stratigraphic and marine magnetic data of the Gulf of Pozzuoli (Naples Bay, Tyrrhenian Sea, Italy): inferences for the tectonic and magmatic events of the Phlegrean Fields volcanic complex (Campania)

    Mar. Geophys. Res.

    (2012)
  • A. Amoruso et al.

    Thermally-assisted magma emplacement explains restless calderas

    Sci Rep

    (2017)
  • M.R. Auker et al.

    A statistical analysis of the global historical volcanic fatalities record

    J. Appl. Volcanol.

    (2013)
  • M. Battaglia et al.

    Evidence for fluid migration as the source of deformation at Campi Flegrei caldera (Italy)

    Geophys. Res. Lett.

    (2006)
  • P.P. Bruno

    Structure and evolution of the Bay of Pozzuoli (Italy) using marine seismic reflection data: implications for collapse of the Campi Flegrei caldera

    Bull. Volcanol.

    (2004)
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