Shallow structures of the marine Campi Flegrei Caldera and the volcanoclastic and sedimentary deposits in the Bay of Naples

• Applicant: Professor Dr. Volkhard Spieß
• Subject Area: Palaeontology ; Geophysics
• Term: from 2012 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 216244414

• Final Report Year: 2018

Final Report Abstract

Caldera-forming eruptions are among the most catastrophic natural events to affect the Earth's surface. The partly-submerged Campi Flegrei caldera (CFc) (southern Italy) represents a prime example of an active, resurgent caldera and, thus, an ideal natural laboratory to study fundamental caldera processes. Due to its history of large-scale explosive eruptions, its ongoing episodes of unrest, and its high population density with nearly 2.5 million people living in the close vicinity, the CFc represents one of the world’s maximum volcanic risk areas. Hence, it has also become subject to ICDP drilling (Campi Flegrei Deep Drilling Project; CFDDP) as well as to a concurrently submitted IODP pre-proposal (671-pre), with the overarching objective of understanding the most explosive and dangerous volcanism on Earth related to large collapse calderas. To support this amphibian approach, a novel high-resolution multichannel seismic (MCS) dataset was acquired in 2008 (CAFE-7/3) in the offshore sector of the CFc and the greater vicinity of the Gulf of Naples, providing a detailed image of the upper 200 m of the caldera. In particular, an unprecedented 3D MCS (50 N-S trending profiles with 120-150 m line spacing) provided a unique opportunity to analyse caldera-related processes in interplay with sedimentation in space and time. Within the scope of this project, the acquired MCS data were to be processed and interpreted to serve as site survey database. Scientifically, the project aimed at contributing to the overall knowledge of caldera volcanism by examining (1) the caldera architecture and collapse mechanisms, (2) post-caldera volcano-tectonic processes, (3) hydrothermal activity in the shallow subsurface, and (4) the interplay between tectonism and volcanic activity at the CFc. For the first time, high-resolution MCS data showed evidence for the existence of a nested-caldera system formed during two collapses associated with the Campanian Ignimbrite (CI, 39 ka) and the more recent Neapolitan Yellow Tuff (NYT, 15 ka) eruptions. An arc-shaped inner caldera fault separating the caldera margin from the subsided caldera depression was clearly imaged and spatially mapped. This fault has at least partially been active during both the CI and NYT eruptions. Furthermore, evidence for the existence of a deeper fracture zone, exclusively formed in the course of the CI eruption, was found. Moreover, the MCS data revealed that the fractured caldera margin has acted as pathway for the ascent of hydrothermal fluids potentially originating from the hypothesised shallow hydrothermal system. Overall it seems that the ascent of magma and hydrothermal fluids is mainly controlled by the outer caldera fault, while the inner fault only plays a subordinated role. In the broader sense this may indicate that the outer caldera ring-fault represents a more likely location for a future eruption. The analysis of regional MCS profiles from the Gulf of Naples suggested a close linkage between tectonism and volcanism, probably related to the reactivation of major NE-SW and NW-SE-trending normal faults in the time periods between (1) 1 and 0.40 Ma and (2) 0.14 and 0.02 Ma. Therefore, it was hypothesised that the CI (39 ka) was triggered by regional tectonism, while no evidence for the linkage between the tectonism and the more recent NYT eruption (15 ka) were found. The main outcomes of the project are three novel evolutionary models addressing (1) the formation of the Campi Flegrei nested-caldera complex, (2) the 3D post-caldera evolution of the CFc, and (3) a 3D reconstruction of the tectono-sedimentary variability in the Gulf of Naples half-graben with respect to volcanism during the past one million years. In summary, the project’s findings represent a significant advancement towards understanding of the genesis and evolution of CFc in particular but also of calderas in general. The suitability of MCS data to investigate (partly) submerged collapse was underlined and may also be applicable to other calderas.

Publications

• 2016. Reconstruction of volcano-tectonic processes in interplay with sedimentary deposition in the Gulf of Naples (Italy) using a seismoacoustic dataset. Dissertation, University of Bremen
  Steinmann, L.
  
• 2014. Reconstruction of volcano-tectonic processes in the offshore sector of the Campi Flegrei caldera. 5th International Workshop on Collapse Calderas, 7-11 December 2014, Taupo, New Zealand
  Steinmann, L., Spiess, V., Sacchi, M.
  
• 2015. The interplay of volcanic, tectonic and sedimentary processes in the offshore sector of the Campi Flegrei caldera (Gulf of Naples, Italy): Preliminary results of a multi-channel seismic Pre-Site Survey for combined IODP and ICDP drilling campaigns. IODP/ICDP colloquium, 17-19 March 2014, Nuremberg, Germany
  Steinmann, L., Spiess, V., Sacchi, M.
  
• 2016. The Campi Flegrei caldera (Italy): formation and evolution in interplay with sea-level variations since the Campanian Ignimbrite eruption at 39 ka. Journal of Volcanology and Geothermal Research, 327, 361-374
  Steinmann, L., Spiess, V., Sacchi, M.
  
• 2016. The Evolution of the Campi Flegrei caldera (Italy): High- and low-frequency multichannel 2.5D seismic surveying for an amphibian IODP/ICDP drilling approach. EGU, 17-22 April 2016, Vienna, Austria
  Steinmann, L., Spiess, V., Sacchi, M.
  
• 2018. Post-collapse evolution of a coastal caldera system: Insights from a 3D multichannel seismic survey from the Campi Flegrei caldera (Italy). Journal of Volcanology and Geothermal Research, 349, 83-98
  Steinmann, L., Spiess, V., Sacchi, M.