The INGV monitoring system operating in the volcano Island since three decades, recorded a new phase of unrest at the La Fossa volcano since September 2021. The main set of the crisis was the central hydrothermal system, deeply affected by the input of heat and chemicals from the magmatic source. The Levante Bay, located northwest of the La Fossa edifice, is a thermal area, where the vapor, coming from a local hydrothermal aquifer, is emitted from several low temperature (100°C) fumaroles along the beach and in the near off shore. The composition of the gas is typical of hydrothermal systems, and indicates equilibrium at temperature close to 200°C. By the onset of the crisis, in September 2021, the composition of the gas emitted from these fumaroles showed a smooth trend of increasing contribution of the magmatic gas. In May 2022, a sudden release of gas occurred in the Levante Bay, which was testified by the whitening of the seawater in the bay, due the formation of sulfur flakes, and by the appearance of typical pockmark structures on the seafloor. The drastic increase of the gas flux from the underwater gas vents, coupled to the presence of the pockmarks, suggested that an explosive emission of gas occurred in May 2022. The chemical and isotopic composition (He and C isotopes) of the gas emitted from the fumaroles revealed the prevailing presence of the magmatic component, closely approaching the composition of the gas emitted from crater fumaroles. This episode drove the attention of the scientific community to this area, currently affected by a significant input of the magmatic vapor, because of the risk related to the huge gas emission and the eventual overpressurization of the local hydrothermal aquifer.

Passive acoustic may represents a sustainable and safe method for long-term investigation of hydrothermal vents, as direct measures can be challenging due to the extreme environmental conditions (high temperature and acidic fluids) as demonstrated in the recent past [Heinicke, et al. 2009, Longo et al. 2021]. Here we present preliminary results of short-term monitoring of the submarine hot hydrothermal spring located in the hydrothermal field within the islets about 2 nautical miles E of Panarea island, in the NE sector of Aeolian arc (Aeolian Island, Italy). The so-called “Black Point” spring shows peculiar characteristics with respect to to the surrounding field; it is featured by extremely high temperatures close to 140 °C, very low pH (with values spanning between 2.8-3.5) and dark/brown fluid emissions from the vent [Italiano and Nuccio, 1991, Müller 2011].The main scope of the present work is to describe for the first time the spectral signature of the shallow hydrothermal brine using non invasive passive acoustic methods and to provide a useful and long-life tool to track the flow rate evolution along the time. High resolution acoustic records were collected using a dedicated battery powered smart hydrophone installed in the proximity of the thermal emission in different periods, providing a panoramic view of the investigated phenomena. The application of various methods of spectral analysis and metadata extrapolation permitted the identification of different energetic frequency peaks and narrow tones, diverging from the ambient background noise, depicting distinct features in terms of bandwidth and energy levels. The bandwidth extension, comprising both infrasonic and audible bands, suggest the coexistence of different source mechanisms, as previously highlighted in different deep hydrothermal sites [Little et al. 1990, Crone TJ et al. 2006, Smith and Barclay 2021]. The application of customised thresholding algorithms allowed the identification of the acoustic source related to bubble nucleation processes induced by the turbulent flowing fluid throughout uneven conduits. Afterwards, the analysis of the PSDs of each record emphasised the temporal evolution of both the power spectral levels and the frequency peaks during the observing period.Preliminary results show persistent and almost constant contributions in well defined frequency range. Frequency shifts testify a behaviour change of the hydrothermal vent turbulence due to natural forces. Furthermore, vibrational induced signals and the presence of narrow tonal components, due to the conversion of seismic energy into acoustic waves along the solid-liquid interface, were identified in the range [50 - 150] Hz, underlying the complexity of mechanisms and the hidden information that can be extracted from the hydrothermal area. In addition, coupling short-time passive acoustic with multidisciplinary data coming from the pre-existing fixed underwater infrastructure, it was possible to observe the evolution of the hydrothermal field activity over time. The ongoing research demonstrates how a deep understanding of the acoustic sources could shed light over the behaviour of the hydrothermal reservoir, acting as a powerful proxy to identify fluid flux change induced by magmatic contribution over long-term deployments.

Marine hydrothermal ecosystems represent extreme environments connected to submarine volcanic areas characterized by vents, having high temperatures and particular chemical compositions. The hydrothermal marine system of Panarea, located in one of the seven small islands belonging to the Aeolian Archipelago (southern Tyrrhenian Sea), is characterized by a range of vents exhibiting diverse physical and chemical conditions. We aimed to analyze the microbial community of a peculiar hot spring belonging to the Panarea hydrothermal field, known as “Black Point” (BP), in two separate sampling expeditions (May and August). Our results demonstrated that the chemical–physical variations within this hydrothermal vent, such as temperature fluctuations, mineral content, and hydrothermal fluid dynamics, play a role in shaping the structure and diversity of microbial communities. The differences between the two sampling expeditions suggest that seasonal changes, i.e., in temperature, pH, and redox potential (Eh), could drive microbial community shifts over time.

Within the framework of SANTORY (SANTORini’s seafloor volcanic observatorY) project, funded by the Hellenic Foundation for Research and Innovation and with the financial support of the Municipality of Thira, three oceanographic cruises were performed in December 2022 and June and October 2023, with the research vessels PHILIA and AEGAEO of the HCMR at the submarine volcano Kolumbo, 7 km NE of Santorini. Kolumbo is considered to be one of the most active submarine volcanic complexes in the Eastern Mediterranean Sea, while being easily accessible from land.. The oceanographic surveys were mainly aimed at the deployment of a new generation observatory along with several multiple innovative sensors such as temperature sensors, inclinometers, pressure gauges, optical cameras, multispectral and stereo camera, radioactivity sensor gSniffer and the γ-radiation imager. During the surveys, several water column profiles were also performed in order to collect seawater samples for chemical analysis. At the bottom of the Kolumbo crater (500m depth), acidic and slightly reducing conditions prevail, due to the presence of several active hydrothermal vents. This agrees with previous studies and with the data recorded by the deployed observatory. Collected samples have been analyzed for the chemical and isotope (carbon, helium and argon) composition of the dissolved gases as well as for the major, minor and trace element concentrations. The results indicate that the morphology of the crater allows the buildup of persistent anomalies that extend from the bottom up to the lowest crater-rim level at about 250-meter depth. We will discuss the temporal variability of the Kolumbo venting dynamics and the explore in detail the resulting vertical gradients in the crater funnel.

Submarine hydrothermal systems attract increasing interest from the scientific community, as they emit huge amounts of both elements and energy. However, in relation to their extreme environmental conditions (e.g. high temperature and pressure, low Ph) direct measurements can be challenging to perform.In this context, passive hydroacoustics may represent a powerful technique for both short- and long-term monitoring as the typical source mechanisms of the hydrothermal fields, directly related to ascending fluids, radiate sound pressure following different acoustic modes.Here we present preliminary results obtained by using a spectral approach for estimating the gas flow emission rate starting from the acoustic dataset collected between 22nd and 26th August 2022 on a stationary flux vent located at ~1.8 metres depth, inside the shallow hydrothermal field at Baia di Levante in Vulcano island (Aeolian Islands, Italy).To carry out the estimation of the gas flow emission rate emitted by the hydrothermal vent, we implemented a customised inverse modelling algorithm based on a spectral method founded upon the assumption that the acoustic signature of a single bubble event evolves over time as a sinusoid that exponentially decays. According to this approach, we refined the formulation of a forward model for the sound radiated by a stationary, high-flux bubbles’ plume, then the path was backward analysed through the proposed inversion algorithm, which allowed us to obtain the estimated value of the flow emission rate.High-resolution audio frames were recorded by using hydrophones [1 - 12800] Hz, that were deployed in the proximity of the investigated vent, collecting a total amount of 7 bursts of ~10 hour-long each. Preliminary analyses of the Power Spectral Density (PSD) and Pressure Power Spectrum highlighted the presence of different persistent energetic frequency peaks over the environmental background noise coherently with the dynamics of the hydrothermal field. The most energetic ones, likely due to the acoustic signal radiated by a large, resonant bubble plume, consistently confirmed the coupling of the estimated radius with direct observations. The performed analysis allowed us to identify the main features of the vent, characterised by bubbles radii up to 0.03 m that produce the main energetic peak centred at ~100 Hz, along with smaller bubbles generating less energetic peaks up to 2 kHz. Therefore, the algorithm was set to work in a wide frequency range, spanning from 60 Hz to 2060 Hz, in order to estimate all the gas released by the vent.The estimated flow emission rate for the investigated period retrieved values spanning from 3.31 to 6.98 litres per minute, with a mean value of 4.97 litres per minute, in good agreement with the direct observations. These results confirm that passive acoustic methods represent a valid and robust tool for both monitoring and research activity in submarine hydrothermal fields, providing a long-lasting instrument able to detect the fluctuations connected to the variations of such natural systems.