Longo, Manfredi

Late Quaternary crustal uplift is well recognized in northeast Sicily, southern Italy, a region also prone to damaging earthquakes such as the 1908 “Messina” earthquake (Mw 7.1), the deadliest seismic event reported within the Italian Earthquake Catalogue. Yet it is still understudied if, within the Milazzo Peninsula, crustal uplift rates are varying spatially and temporally and whether they may be either influenced by (i) local upper-plate faulting activity or (ii) deep geodynamic processes. To investigate the long-term crustal vertical movements in northeast Sicily, we have mapped a flight of Middle-Late Pleistocene marine terraces within the Milazzo Peninsula and in its southern area and refined their chronology, using a synchronous correlation approach driven by published age controls. This has allowed a new calculation of the associated crustal uplift rates, along a north–south oriented coastal-parallel transect within the investigated area. Our results show a decreasing uplift rate from south to north across the Milazzo Peninsula and beyond, and that the associated rates of uplift have been constant through the Late Quaternary. This spatially varying yet temporally constant vertical deformation helps to constrain the amount of uplift, allowing us to explore which is the driving mechanism(s), proposing a few related scenarios. We discuss our results in terms of tectonic implications and emphasize the importance of using appropriate approaches, as such applying a synchronous correlation method, to refine chronologies of undated palaeoshorelines when used for tectonic investigations.

The concepts of CO2 emission, global warming, climate change, and their environmental impacts are of utmost importance for the understanding and protection of the ecosystems. Among the natural sources of gases into the atmosphere, the contribution of geogenic sources plays a crucial role. However, while subaerial emissions are widely studied, submarine outgassing is not yet well understood. In this study, we review and catalog 122 literature and unpublished data of submarine emissions distributed in ten coastal areas of the Aegean Sea. This catalog includes descriptions of the degassing vents through in situ observations, their chemical and isotopic compositions, and flux estimations. Temperatures and pH data of surface seawaters in four areas affected by submarine degassing are also presented. This overview provides useful information to researchers studying the impact of enhanced seawater CO2 concentrations related either to increasing CO2 levels in the atmosphere or leaking carbon capture and storage systems.

Submarine hydrothermal systems along active volcanic ridges and arcs are highly dynamic, responding to both oceanographic (e.g., currents, tides) and deep-seated geological forcing (e.g., magma eruption, seismicity, hydrothermalism, and crustal deformation, etc.). In particular, volcanic and hydrothermal activity may also pose profoundly negative societal impacts (tsunamis, the release of climate-relevant gases and toxic metal(loid)s). These risks are particularly significant in shallow (<1000m) coastal environments, as demonstrated by the January 2022 submarine paroxysmal eruption by the Hunga Tonga-Hunga Ha’apai Volcano that destroyed part of the island, and the October 2011 submarine eruption of El Hierro (Canary Islands) that caused vigorous upwelling, floating lava bombs, and natural seawater acidification. Volcanic hazards may be posed by the Kolumbo submarine volcano, which is part of the subduction-related Hellenic Volcanic Arc at the intersection between the Eurasian and African tectonic plates. There, the Kolumbo submarine volcano, 7 km NE of Santorini and part of Santorini’s volcanic complex, hosts an active hydrothermal vent field (HVF) on its crater floor (~500m b.s.l.), which degasses boiling CO2–dominated fluids at high temperatures (~265°C) with a clear mantle signature. Kolumbo’s HVF hosts actively forming seafloor massive sulfide deposits with high contents of potentially toxic, volatile metal(loid)s (As, Sb, Pb, Ag, Hg, and Tl). The proximity to highly populated/tourist areas at Santorini poses significant risks. However, we have limited knowledge of the potential impacts of this type of magmatic and hydrothermal activity, including those from magmatic gases and seismicity. To better evaluate such risks the activity of the submarine system must be continuously monitored with multidisciplinary and high resolution instrumentation as part of an in-situ observatory supported by discrete sampling and measurements. This paper is a design study that describes a new long-term seafloor observatory that will be installed within the Kolumbo volcano, including cutting-edge and innovative marine-technology that integrates hyperspectral imaging, temperature sensors, a radiation spectrometer, fluid/gas samplers, and pressure gauges. These instruments will be integrated into a hazard monitoring platform aimed at identifying the precursors of potentially disastrous explosive volcanic eruptions, earthquakes, landslides of the hydrothermally weakened volcanic edifice and the release of potentially toxic elements into the water column.

The Black Sea bottom is well known to be earth’s largest anaerobic methane source, hosting a huge amount of cold seeps releasing significant volumes of methane of both thermogenic and biogenic origin. Taking into account the well-known effects of methane concerning global warming, including the warming up of the oceans, an effective monitoring of its output from the Black Sea is nowadays an essential target for interdisciplinary studies. We discuss the results achieved during monitoring campaigns aimed to detect and track methane flares from the seafloor of the Romanian sector of the Black Sea, in order to better constrain the possible mechanisms responsible for its injection from the marine sediments, through the water column, into the atmosphere. In the mainframe of the ENVRI-Plus project, we deployed a multidisciplinary seafloor observatory for short, mid and long time monitoring and collected samples of the water column. The multidisciplinary seafloor observatory was equipped with probes for passive acoustic signals, dissolved CH4 and chemical-physical parameters. The collected data showed a high concentration of dissolved methane up to values of 5.8 micromol/L. Passive acoustics data in the frequencies range 40–2,500 Hz allow us to discriminate different degassing mechanisms and degassing styles. The acoustic energy associated with gas bubbling is interpreted as a consequence of the gas dynamics along the water column while the acoustic range 2–20 Hz reveals vibration mechanisms generated by gas dynamic’s along the cracks and inside the sediments.

Greece belongs to the most geodynamically active regions of the world and as such, it has to be considered an area of intense geogenic degassing. In terms of carbon, the territory is characterized by the high hydrothermal and volcanic activity of the South Aegean Active Volcanic Arc (SAAVA), and by widespread geological seeps of buried carbon dioxide and methane. In the present work, we investigate the island of Gyali located in the volcanic system Kos-Gyali-Nisyros. Nine gas samples have been collected on the island of Gyali in areas found both on land, in a small lake (~2000 m2) along its beach, and in the sea close to the shore at shallow depths (<20 m). Results show that CO2 is the prevailing gas species with concentrations above 833,000 μmol/mol, whilst minor enrichments in N2 are noticed in some of the samples. Helium isotope ratio suggests an up to 70% mantle origin (considering a MOR type source) with the contribution of the atmospheric component being negligible, whereas C presents a mixed mantle-limestone origin with organic sediment being unimportant. Such isotope values fall in the range that characterizes the Kos-Gyali-Nisyros Volcanic Field. First estimations on the CO2 release suggest an output in the range from 18 to 28 t/d for Gyali Island, which is much lower than the total output of Kos ~75 t/d and Nisyros ~100 t/d. However, such results highlight that Gyali is an active system and, despite its small size, its degassing is not trivial.

We present the results from a mid-term monitoring activity carried out at the submarine hydrothermal system located off Panarea Island (Aeolian Islands, Italy). The collected data concern multiparametric information from a self-operating seafloor station (acoustics and chemical–physical parameters) acquiring data at regular intervals and transmitting it twice a day in near real-time. The acoustic records were analysed with the principal aim of investigating bubbling variations related to gas flow rate. Several anomalies have been documented, in the bubbling activity detected at high frequencies (100–2000 Hz), as well as in very low acoustic frequencies, related to fluids dynamic along cracks. An astonishing correlation between soil CO2 flux emissions recorded at Stromboli craters and the acoustic signals in the 1–30 Hz range has been identified, suggesting how this tectonic link could act as an escape route for fluids characterized by a shared source.

We report on original geochemical data, which combine the rainfall trace metal contents from three different areas of Mt. Etna, variably fumigated by the volcanic plume, and those from soils, collected over the whole volcano. Trace element contents in rainfall appear mostly related to acidic ash leaching, while only for the most volatile elements (Cu, Zn, Cd, Pb, As, Sb, Tl, Se). We analyzed separately the labile fraction of soil samples, considered the fraction bioavailable to plants and soil organisms living in. The complexing medium used to extract the bioavailable fraction simulates the growth environment of plant roots.The contents of trace elements in the bioavailable fraction from soil samples showed peculiar patterns, apparently unrelated to the plume fumigation. The transition metal contents in the bioavailable fraction account for less than 15 % of the pseudo-total fraction and the highest contents were measured in the less acidic soil samples and farthest from the summit craters. In particular, high Fe, Mn, Co, Ni, Pb, Zn, Cd contents were paralleled by high soil organic carbon concentrations, which increased in the samples collected downwind the summit vents. Concerning immobile elements, their abundance in the bioavailable fraction was related to the degree of alteration of soils. Two elements, Se and Tl, were enriched in soil samples collected at closer distance from the summit vents. Their origin is probably related to the plume deposition.The study highlighted that the accessibility of plants to potentially harmful trace elements present in the soil is not simply related to the exposure to pollutants, but also to their fate in the pedogenetic environment.

Forty five gas samples have been collected from natural gas manifestations at the island of Kos, the majority of which is found underwater along the southern coast of the island. On land, two anomalous degassing areas have been recognized. These areas are mainly characterised by lack of vegetation and after long dry periods by the presence of sulfate salt efflorescences. Carbon dioxide is the prevailing gas species (ranging from 88 to 99 %), whilst minor amounts of N2 (up to 7.5 %) and CH4 (up to 2.1 %) are also present. Significant contents of H2 (up to 0.2 %) and H2S (up to 0.3 %) are found in the on-land manifestations. Only one of the underwater manifestations is generally rich in N2 (up to 98.9 %) with CH4 concentrations up to 11.7 % and occasionally extremely low CO2 amounts (down to 0.09 %). Isotope composition of He ranges from 0.85 to 6.71 R/RA, indicating a sometimes strong mantle contribution; the highest values measured are found in the two highly degassing areas of Paradise Beach and Volcania. C-isotope composition of CO2 ranges from -20.1 to 0.64 ‰ vs V-PDB, with the majority of the values being concentrated around -1 ‰ and therefore proposing a mixed mantle – limestones origin. Isotope composition of CH4 ranges from -21.5 to +2.8 ‰ vs V-PDB for C and from -143 to +36 ‰ vs V-SMOW for H, pointing to a geothermal origin with sometimes evident secondary oxidation processes. The dataset presented in this work consists of sites that were repeatedly sampled in the last few years, with some of which being also sampled just before and immediately after the magnitude 6.6 earthquake that occurred on the 20th of July 2017 about 15 km ENE of the island of Kos. Changes in the degassing areas along with significant variations in the geochemical parameters of the released gases were observed both before and after the seismic event, however no coherent model explaining those changes was obtained. CO2-flux measurements showed values up to about 104 g×m-2×d-1 in the areas of Volcania and Kokkinonero, 5×104 g×m-2×d-1 at Paradise beach and 8×105 g×m-2×d-1 at Therma spring. CO2 output estimations gave values of 24.6, 16.8, 12.7 and 20.6 t×d-1 respectively for the above four areas. The total output of the island is 74.7 t×d-1 and is comparable to the other active volcanic/geothermal systems of Greece (Nisyros, Nea Kameni, Milos, Methana and Sousaki).

Geochemical investigations carried out on submarine hydrothermal fluids vented offshore the Pontine Islands (Tyrrhenian Sea) revealed the existence of gas vents to the W of Zannone Island and SW of Ventotene Island. The geochemical features of the CO2-rich gas samples show a clear mantle-derived signature with 3He/4He of 3.72-3.75 Ra and 1.33 Ra at Zannone and Ventotene, respectively. Gas geochemistry denotes how CO2-rich gases undergo fractionation processes due to CO2 dissolution to a variable extent favoring enrichment in the less soluble gas species, i.e., CH4, N2, and He. The carbon isotope composition of CO2, expressed as δ13C vs. V-PDB, ranges from -0.71 and -6.16‰ at Zannone to 1.93‰ at Ventotene. Preliminary geothermometric and geobarometric estimations indicate equilibrium temperatures in the range of 150-200°C at Zannone and >200°C at Ventotene besides H2O pressures in the range of 5 bar and 20 bar at Zannone and Ventotene, respectively. Although the latest volcanic activity at the Pontine Archipelago is dated Middle Pleistocene, the combination of the new geochemical information along with geothermometric estimations indicates that cooling magmas are likely releasing enough thermal energy to form an efficient hydrothermal system.

Geohazards associated to submarine hydrothermal systems still represent a tricky enigma to face and solve for the scientific community. The poor knowledge of a submarine environment, the rare and scarce monitoring activities, and the expensive and sometimes complicated logistics are the main problems to deal with. The submarine low-energy explosion, which occurred last November 3, 2002, off the volcanic island of Panarea, highlighted the absence of any hazard scenario to be used to manage the volcanic crisis. The “unrest” of the volcanic activity was triggered by a sudden input of deep magmatic fluids, which caused boiling water at the sea surface with a massive CO2 release besides changes in the fluids’ geochemistry. That event dramatically pushed scientists to develop new methods to monitor the seafloor venting activity. Coupling the information from geochemical investigations and data collected during the unrest of volcanic activity, we were able to (a) develop theoretical models to gain a better insight on the submarine hydrothermal system and its relationships with the local volcanic and tectonic structures and (b) to develop a preliminary submarine volcanic hazard assessment connected to the Panarea system (Aeolian Islands). In order to mitigate the potential submarine volcanic hazard, three different scenarios are described here: (1) ordinary hydrothermal venting, (2) gas burst, and (3) volcanic eruption. The experience carried out at Panarea demonstrates that the best way to face any submarine volcanic-hydrothermal hazard is to improve the collection of data in near real-time mode by multidisciplinary seafloor observatories and to combine it with periodical sampling activity.