Hydrothermal fluid venting in the offshore sector of Campi Flegrei caldera: A geochemical, geophysical, and volcanological study

Abstract

The ongoing unrest at the Campi Flegrei caldera (CFc) in southern Italy is prompting exploration of its poorly studied offshore sector. We report on a multidisciplinary investigation of the Secca delle Fumose (SdF), a submarine relief known since antiquity as the largest degassing structure of the offshore sector of CFc. We combined high-resolution morphobathymetric and seismostratigraphic data with onshore geological information to propose that the present-day SdF morphology and structure developed during the initial stages of the last CFc eruption at Monte Nuovo in AD 1538. We suggest that the SdF relief stands on the eastern uplifted border of a N-S-trending graben-like structure formed during the shallow emplacement of the Monte Nuovo feeding dike. We also infer that the high-angle bordering faults that generated the SdF relief now preferentially allow the ascent of hot brines (with an equilibrium temperature of 1798C), thereby sustaining hydrothermal degassing on the seafloor. Systematic vertical seawater profiling shows that hydrothermal seafloor venting generates a sizeable CO 2 , pH, and temperature anomaly in the overlying seawater column. Data for the seawater vertical profile can be used to estimate the CO 2 and energy (heat) outputs from the SdF area at $50 tons/d ($0.53 kg/s) and $80 MW, respectively. In view of the cause-effect relationship with the Monte Nuovo eruption, and the substantial gas and energy outputs, we consider that the SdF hydrothermal system needs to be included in monitoring programs of the ongoing CFc unrest.

Environmental and Benthic Community Patterns of the Shallow Hydrothermal Area of Secca Delle Fumose (Baia, Naples, Italy)

“…and abundance (19 ind.) are mainly due to the seawater acidification (pH ∼7.6), in agreement with Di Napoli et al (2016) who recently detected acidic CO 2 -rich fluids in the SdF area, and to the high sediment temperature (37.53 ± 2.28 • C), that was almost the double of that detected in the control sites (21.8 • C). These factors produced a reduction of 83.64% in taxonomic richness and 86.29% in number of individuals if compared with those found around the geyser and a reduction of 93.92 and 97.75% respectively if compared with control sites.…”

“…"Secca delle Fumose" (SdF) belongs to the largest degassing structure offshore of the Campi Flegrei caldera. With an extension of approximately 0.14 km 2 , is located about 800 m off the coastline in the north-western part of Pozzuoli Bay (Gulf of Naples, Italy) (40 • 49 23 N 14 • 05 15 E) (Tedesco et al, 1990;Passaro et al, 2013;Di Napoli et al, 2016). In this area, four sampling sites were selected (Figure 1), two control sites (CN; CS) and two in proximity of very different vents: a first characterized by white bacterial mats (H) and a second by yellow substrate around a solitary geyser opening (G).…”

“…A few kilometers away from Ischia Island, in the Campi Flegrei caldera, Di Napoli et al (2016) reported a remarkable variation in seawater pH (∼7.3-8.3) due to the gas-rich hydrothermal fluids occurring in a shallow submarine relief, namely Secca delle Fumose. This area was only recently investigated from a geological (e.g., Tedesco et al, 1990;Passaro et al, 2013) and microbiological (Maugeri et al, 2010), point of view.…”

Source and dynamics of a volcanic caldera unrest: Campi Flegrei, 1983–84

“…The Pozzuoli-Mt. Nuovo connection was seismically active below 2 km depth and followed the caldera-bounding and NW-SE striking offshore normal faults west of Pozzuoli 21 , 50 . These faults were thus aseismic throughout January 1984 and activated between February 10 and March 31, 1984 (Fig.…”

Space‐weighted seismic attenuation mapping of the aseismic source of Campi Flegrei 1983–1984 unrest

“…The objective is to locate and model in space the sources of high fumarolic activity, ground deformation, and hydrothermal activity during the unrest [Todesco et al, 2010;Chiodini et al, 2010;Amoruso et al, 2014a]. The increased lateral illumination with respect to standard Q c imaging may lead to better understanding of the feeding mechanisms active at the volcano at present and historical times [Todesco et al, 2014;Di Napoli et al, 2016;Di Vito et al, 2016], as done at other volcanoes [Prudencio et al, 2015a[Prudencio et al, , 2015b. The study thus gives a different seismic imaging perspective on the problem of locating deformation and unrest sources related to hydrothermal dynamics.…”