ALBERT

Description: Vulcano is one of the 7 volcanic islands and 6 seamounts forming the Aeolian volcanic district (Italy). Vulcano has a long eruptive record, and its last eruption (1888–90 AD) originated the definition of the Vulcanian eruptive style. Like most volcanic islands, Vulcano generates many potentially interconnected hazards, determining a potentially high risk. Here, we review the state of knowledge on its geology, eruptive activity, historical accounts, structural setting, geophysical and geochemical surveillance, and available hazard assessment, in order to have an updated picture of the state knowledge on volcanic hazard. We follow a prototypal reviewing scheme, based on three standardized steps: i) review of the volcanic system; ii) review of available eruptive and noneruptive hazard quantifications; iii) development of a conceptual interpretative model. We find that, while a rather vast literature is dedicated to the volcanic system of Vulcano and the reconstruction of past events, few quantitative hazard assessments exist. In addition, the range of natural variability considered for each hazard is potentially underestimated (e.g. limited range of considered eruption magnitude and style and of vent position), as it is the potential effect of multi-hazard impact. The developed conceptual model for the feeding system provides a synthetic picture of the present knowledge about the system, as emerged from the review. In addition, it allows for the identification of potential paths-to-eruption and provides a first order link among the main hazards. This review provides an up-to-date snapshot of existing knowledge on volcanic hazard at Vulcano on which to build future hazard quantifications as well as to support present and future decision making.

Description: Published

Description: 103186

Description: 1V. Storia eruttiva

Description: JCR Journal

Description: Dikes and sills are the moving building blocks of the plumbing system of volcanoes and play a fundamental role in the accretionary processes of the crust. They nucleate, propagate, halt, resume propagation, and sometimes change trajectory with drastic implications for the outcome of eruptions (Sigmundsson et al., 2010). Their dynamics is still poorly understood, in particular when different external influencing factors are interacting. Here we apply a boundary element model to study dike and sill formation, propagation and arrest in different scenarios. We model dikes as finite batches of compressible fluid magma, propagating quasi-statically in an elastic medium, and calculate their trajectories by maximising the energy release of the magma-rock system. We consider dike propagation in presence of density layering, of density plus rigidity layering, of a weakly welded interface between layers, under the action of an external stress field (of tectonic or topographic origin). Our simulations predict sill formation in several situations: i) when a horizontal weak interface is met by a propagating dike; ii) when a sufficiently high compressive tectonic environment is experienced by the ascending dike and iii) in case a dike, starting below a volcanic edifice, propagates away from the topographic load with a low dip angle. We find that dikes halt and stack when they become negatively buoyant and when they propagate with low overpressure at their upper tip toward a topographic load. Neutral buoyancy by itself cannot induce dikes to turn into sills, as previously suggested.

Description: Published

Description: 39-50

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: Surface tension plays an important role in the nucleation of H2O gas bubbles in magmatic melts and in the time-dependent rheology of bubble-bearing magmas. Despite several experimental studies, a physics based model of the surface tension of magmatic melts in contact with H2O is lacking. This paper employs gradient theory to develop a thermodynamical model of equilibrium surface tension of silicate melts in contact with H2O gas at low to moderate pressures. In the last decades, this approach has been successfully applied in studies of industrial mixtures but never to magmatic systems. We calibrate and verify the model against literature experimental data, obtained by the pendant drop method, and by inverting bubble nucleation experiments using the Classical Nucleation Theory (CNT). Our model reproduces the systematic decrease in surface tension with increased H2O pressure observed in the experiments. On the other hand, the effect of temperature is confirmed by the experiments only at high pressure. At atmospheric pressure, the model shows a decrease of surface tension with temperature. This is in contrast with a number of experimental observations and could be related to microstructural effects that cannot be reproduced by our model. Finally, our analysis indicates that the surface tension measured inverting the CNT may be lower than the value measured by the pendant drop method, most likely because of changes in surface tension controlled by the supersaturation.

Description: Published

Description: 113-127

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Primitive basalticmagmas are crucial in the study of the geochemical heterogeneity documented in Etnamagmas and their inferred mantle sources. We undertook a systematic sampling of the less evolved basalts (Mg# N50) erupted over the last 15 ka, a time period which corresponds to the activity of the youngest volcanic edifice of Mt. Etna complex, i.e. Mongibello volcano. We focused on lava flows and pyroclastites emplaced during ‘deepdyke fed’ (DDF) eruptions which were driven by the rapid ascent of deeply-rooted magma intrusions that bypassed the shallow plumbing system of the volcano. All the samples were analyzed by the same laboratory to avoid analytical bias, to build a comprehensive dataset on their major and trace element compositions and to propose a coherent framework for interpreting the geochemical fingerprints of present-day Etna basalts. Trace element modeling, togetherwith literature data for Sr isotopes, gave insight into long-term magmatic processes related to different melting degrees of the heterogeneous mantle beneath Mt Etna. DDF magma batches provide good snapshots of their mantle source heterogeneities that point to the variable involvement of clinopyroxenitic lithology, Rb–87Sr–Cl-rich fluid component(s) possibly controlled by their source mineralogy, and slab-derived fluids selectively enriched in alkalis (Rb, K). The ongoing alkali (Rb, K) enrichment of the present-day magmas, well manifest since the 1970s, is decoupled from that of Sr and Cl. We propose that this process is linked to mantle source composition and is concomitant with changes in both volcanological and seismotectonic patterns of the volcano. There is no time evolution of DDF magma chemistry.

Description: Published

Description: 123-134

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: A statistical analysis of Loss of Lock (LoL) over Brazil throughout the 24th solar cycle is performed. Four geodetic GPS dual-frequency (L1, L2) receivers, deployed at different geographic latitudes ranging from about 25° to 2° South in the eastern part of the country, are used to investigate the LoL dependence on time of the day, season, solar and geomagnetic activity. The results of the analysis show that LoL is most likely in the post-sunset hours during summer and equinox, especially within the southern crest of the Equatorial Ionospheric Anomaly (EIA), in a region between about 10°S and 25°S of geographic latitude, matching the typical behaviour of scintillation over Brazil. This is confirmed by the correlation found between the relative occurrence of LoL (LoL (%)) and the Rate Of TEC Index (ROTI), used as a proxy of scintillation index and calculated for each receivers along the entire period of investigation. The LoL (%) for given solar and geomagnetic indices show some correlation with increasing the severity of the index. This correlation is strongest in the area of the southern crest of the EIA, while there is little to no apparent impact closer to the equator, depending on the index. LoL (%) increases with increasing geomagnetic disturbances, varying between ~1% and ~10% for AE ranged between 400 and 1200 nT, and exceeding 3% when Dst is around −100 nT, both related to moderate-severely disturbed conditions.

Description: Published

Description: 219-225

Description: 2A. Fisica dell'alta atmosfera

Description: JCR Journal

Description: While mantle convection is a fundamental ingredient of geodynamics, the driving mechanism of plate tectonics remains elusive. Are plates driven only from the thermal cooling of the mantle or are there further astronomical forces acting on them? GPS measurements are now accurate enough that, on long baselines, both secular plate motions and periodic tidal displacements are visible. The now 〉20 year-long space geodesy record of plate motions allows a more accurate analysis of the contribution of the horizontal component of the body tide in shifting the lithosphere. We review the data and show that lithospheric plates retain a non-zero horizontal component of the solid Earth tidal waves and their speed correlates with tidal harmonics. High-frequency semidiurnal Earth's tides are likely contributing to plate motions, but their residuals are still within the error of the present accuracy of GNSS data. The low-frequency body tides rather show horizontal residuals equal to the relative motion among plates, proving the astronomical input on plate dynamics. Plates move faster with nu- tation cyclicities of 8.8 and 18.6 years that correlate to lunar apsides migration and nodal precession. The high- frequency body tides are mostly buffered by the high viscosity of the lithosphere and the underlying mantle, whereas low-frequency horizontal tidal oscillations are compatible with the relaxation time of the low-velocity zone and can westerly drag the lithosphere over the asthenospheric mantle. Variable angular velocities among plates are controlled by the viscosity anisotropies in the decoupling layer within the low-velocity zone. Tidal oscillations also correlate with the seismic release.

Description: Published

Description: 103179

Description: 1T. Struttura della Terra

Description: JCR Journal

Description: Many long-term monitoring sites in Antarctic regions, which deploy ground-based stratospheric remote sensors and fly radiosondes or ozonesondes on balloons, supported the Airborne Polar Experiment in September and October 1999. Support consisted of supplying data to the campaign in real time, and in some cases by increasing the frequency of measurements during the campaign. The results will strengthen scientific conclusions from the airborne measurements. But results from these sites are allowing important scientific studies of new aspects of the ozone hole in their own right, because like the aircraft and its campaign, many sites traverse the vortex edge and are close to the largest source of lee waves, or measure infrequently observed trace gases such as HNO3. Examples of such studies are the behaviour and value of NO2 in midwinter, ozone filamentation with no apparent horizontal advection, the frequency and amplitude of gravity waves over the Antarctic Peninsula, mixing in the lowest stratosphere in Antarctic spring, the mechanism and frequency of HNO3 enhancement above the ozone peak in midwinter, and trends in UV dose in southern South America.

Description: Published

Description: 835–845

Description: 5A. Ricerche polari e paleoclima

Description: JCR Journal

Description: In the last decades, a growing number of works has increasingly focused on the study of thermal waters using the approach described by Giggenbach (1988). Based on the dependence on temperature of the equilibrium constants, the Na-K-Mg diagram is the combination of the Na-K and K-Mg geothermometers. The pristine approach proposed by Giggenbach (1988) included several constraints for its successful application. In spite of this, the Na-K-Mg diagram is often used out of the boundaries conditions of applicability. In order to promote a proper use of the diagram, a detailed description is given and several examples of mixing, dilution and concentration are discussed. The obtained findings highlight the need of cautiousness when using the diagram to estimate temperature of hydrothermal systems.

Description: Published

Description: 119577

Description: 4V. Processi pre-eruttivi

Description: 1TR. Georisorse

Description: JCR Journal

Description: Vesiculation of crystallising magma can produce either a mobile vesicular magma or a rigid network of crystals containing vesicular liquid. Where partially crystallized rigid mush underlies less-crystallized magma, such as near the base of a lava flow or in the cumulus pile of a magma chamber, evolved interstitial melt and/or gas may escape into the main body of magma. The consequences of this may include contamination of the overlying liquid with gas and interstitial melt, or intrusion of diapirs of vesicular evolved liquids to form vertical vesicle cylinders and other segregation features found in many basaltic lava flows and sills. Analog experiments were used to investigate some of the phenomena that can arise during vesiculation within a crystal mush, which was simulated by pumping air through a porous plate that formed the floor of a container filled with a viscous liquid floored with a layer of glass beads. Experiments used either a single liquid or two stably stratified liquids with a liquid interface either coincident with the top of the porous layer of beads or slightly above the porous layer. For a range of liquid viscosities and air flow rates (vesiculation rates), individual bubbles emerged from the top of the porous layer of beads and carried a thin trail of interstitial liquid into the overlying liquid. The number of bubble trains leaving the surface of the porous bed increased with decreasing liquid viscosity and flow rate, and with increasing bead size (and, hence, with increasing permeability). Analog vesicle cylinders, composed of diapirs of bubbly interstitial liquid, were produced only when a layer of buoyant bubbly liquid lay above the surface of the porous layer. The relative size of the bubbles and constrictions within the porous layer are argued to control whether individual bubbles (leading to bubble trains) or vesicular liquid (leading to vesicle cylinders) leaves the porous layer and hence whether vesicle cylinders can form.

Description: Published

Description: 287–300

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: In the last few decades, advanced monitoring networks have been extended to the main active volcanoes, providing warnings for variations in volcano dynamics. However, one of the main tasks of modern volcanology is the correct interpretation of surface-monitored signals in terms of magma transfer through the Earth's crust. In this frame, it is crucial to investigate decompression-induced magma degassing as it controls magma ascent towards the surface and, in case of eruption, the eruptive style and the atmospheric dispersal of tephra and gases. Understanding the degassing behaviour is particularly intriguing in the case of poorly explored evolved alkaline magmas. In fact, these melts frequently feed hazardous, highly explosive volcanoes (e.g., Campi Flegrei, Somma-Vesuvius, Colli Albani, Tambora, Azores and Canary Islands), despite their low viscosity that usually promotes effusive and/or weakly explosive eruptions. Decompression experiments, together with numerical models, are powerful tools to examine magma degassing behaviour and constrain field observations from natural eruptive products and monitoring signals. These approaches have been recently applied to evolved alkaline melts, yet numerous open questions remain. To cast new light on the degassing dynamics of evolved alkaline magmas, in this study we present new results from decompression experiments, as well as a critical review of previous experimental works. We achieved a comprehensive dataset of key petrological parameters (i.e., 3D textural data for bubbles and microlites using X-ray computed microtomography, glass volatile contents and nanolite occurrence) from experimental samples obtained through high temperature-high pressure isothermal decompression experiments on trachytic alkaline melts at super-liquidus temperature. We explored systematically a range of final pressures (from 200 to 25 MPa), decompression rates (from 0.01 to 1 MPa s−1), and volatile (H2O and CO2) contents. On these grounds, we integrated coherently literature data from decompression experiments on evolved alkaline (trachytic and phonolitic) melts under various conditions, with the aim to fully constrain the degassing mechanisms and timescales in these magmas. Finally, we simulated numerically the experimental conditions to evaluate strengths and weaknesses in decrypting degassing behaviour from field observations. Our results highlight that bubble formation in evolved alkaline melts is primarily controlled by the initial volatile (H2O and CO2) content during magma storage. In these melts, bubble nucleation needs low supersaturation pressures (≤ 50–112 MPa for homogeneous nucleation, ≤ 13–25 MPa for heterogeneous nucleation), resulting in high bubble number density (~ 1012–1016 m−3), efficient volatile exsolution and thus in severe rheological changes. Moreover, the bubble number density is amplified in CO2-rich melts (mole fraction XCO2 ≥ 0.5), in which continuous bubble nucleation predominates on growth. These conditions typically lead to highly explosive eruptions. However, moving towards slower decompression rates (≤ 10−1 MPa s−1) and H2O-rich melts, permeable outgassing and inertial fragmentation occur, promoting weakly explosive eruptions. Finally, our findings suggest that the exhaustion of CO2 at deep levels, and the consequent transition to a H2O-dominated degassing, can crucially enhance magma vesiculation and ascent. In a hazard perspective, these constraints allow to postulate that time-depth variations of unrest signals could be significantly weaker/shorter (e.g., minor gas emissions and short-term seismicity) during major eruptions than in small-scale events.

Description: Published

Description: 103402

Description: 1V. Storia eruttiva

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: 4V. Processi pre-eruttivi

Description: 5V. Processi eruttivi e post-eruttivi

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: The dichotomy between explosive volcanic eruptions, which produce pyroclasts, and effusive eruptions, which produce lava, is defined by the presence or absence of fragmentation during magma ascent. For lava fountains the distinction is unclear, since the liquid phase in the rising magma may remain continuous to the vent, fragment in the fountain, then re-weld on deposition to feed rheomorphic lava flows. Here we use a numerical model to constrain the controls on basaltic eruption style, using Kilauea and Etna as case studies. Based on our results, we propose that lava fountaining is a distinct style, separate from effusive and explosive eruption styles, that is produced when magma ascends rapidly and fragments above the vent, rather than within the conduit. Sensitivity analyses of Kilauea and Etna case studies show that high lava fountains (〉50 m high) occur when the Reynolds number of the bubbly magma is greater than ∼0.1, the bulk viscosity is less than 10^6, and the gas is well-coupled to the melt. Explosive eruptions (Plinian and sub-Plinian) are predicted over a wide region of parameter space for higher viscosity basalts, typical of Etna, but over a much narrower region of parameter space for lower viscosity basalts, typical of Kilauea. Numerical results show also that the magma that feeds high lava fountains ascends more rapidly than the magma that feeds explosive eruptions, owing to its lower viscosity. For the Kilauea case study, waning ascent velocity is predicted to produce a progressive evolution from high to weak fountaining, to ultimate effusion; whereas for the Etna case study, small changes in parameter values lead to transitions to and from explosive activity, suggesting that eruption transitions may occur with little warning.

Description: RCUK NERC DisEqm project

Description: Published

Description: 116658

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Rare Earth Elements (REE; lanthanides and yttrium) are elements with high economic interest because they are critical elements for modern technologies. This study mainly focuses on the geochemical behavior of REE in hyperacid sulphate brines in volcanic-hydrothermal systems, where the precipitation of sulphate minerals occurs. Kawah Ijen lake, a hyperacid brine hosted in the Ijen caldera (Indonesia), was used as natural laboratory. ∑REE concentration in the lake water is high, ranging from 5.86 to 6.52 mg kg-1. The REE pattern of lake waters normalized to the average local volcanic rock is flat, suggesting isochemical dissolution. Minerals spontaneously precipitated in laboratory at 25 °C from water samples of Kawah Ijen were identified by XRD as gypsum. Microprobe analyses and the chemical composition of major constituents allow to identify possible other minerals precipitated: jarosite, Al-sulphate and Sr, Ba-sulphate. ∑REE concentration in minerals precipitated (mainly gypsum) range from 59.53 to 78.64 mg kg-1. The REE patterns of minerals precipitated normalized to the average local magmatic rock show enrichment in LREE. The REE distribution coefficient (KD), obtained from a ratio of its concentration in the minerals precipitated (mainly gypsum) and the lake water, shows higher values for LREE than HREE. KD-LREE/KD-HREE increases in the studied samples when the concentrations of BaO, MgO, Fe2O3, Al2O3, Na2O and the sum of total oxides (except SO3 and CaO) decrease in the solid phase. The presence of secondary minerals different than gypsum can be the cause of the distribution coefficient variations. High concentrations of REE in Kawah Ijen volcanic lake have to enhance the interest on these environments as possible REE reservoir, stimulating future investigations. The comparison of the KD calculated for REE after mineral precipitation (mainly gypsum) from Kawah Ijen and Poás hyperacid volcanic lakes allow to generalize that the gypsum precipitation removes the LREE from water.

Description: Published

Description: 140133

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: 2IT. Laboratori analitici e sperimentali

Description: JCR Journal

Description: The partitioning of carbon dioxide (CO〈sub〉2〈/sub〉) released by soils at Vulcano Island (Aeolian Islands, Italy) was performed by combining the CO〈sub〉2〈/sub〉 flux and the carbon isotope measurements. Based on this method, the amount of CO〈sub〉2〈/sub〉 of volcanic origin was quantified six times during the period 2015–2018. The data analysis allowed us to establish the correlation between CO〈sub〉2〈/sub〉 soil degassing and changes in the contribution of volcanic fluids. Carbon isotope determinations were performed in situ to enhance the coverage of data collection in space and time. These data were combined with both the CO〈sub〉2〈/sub〉 contents in the ground gases and the soil CO〈sub〉2〈/sub〉 flux. The amount of volcanic CO〈sub〉2〈/sub〉 was distinguished from that of biogenic origin by implementing a three-component mixing model. The results of this study indicate that the increase in CO〈sub〉2〈/sub〉 output in September 2018 reflects the increase in volcanic gas emissions. The measurement method and analysis presented in this work are sufficiently general to be applicable to the monitoring programs of active volcanoes.

Description: Published

Description: 106972

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Calderas are topographic depressions formed by the collapse of a partly drained magma reservoir. At volcanic edifices with calderas, eruptive fissures can circumscribe the outer caldera rim, be oriented radially and/or align with the regional tectonic stress field. Constraining the mechanisms that govern this spatial arrangement is fundamental to understand the dynamics of shallow magma storage and transport and evaluate volcanic hazard. Here we show with numerical models that the previously unappreciated unloading effect of caldera formation may contribute significantly to the stress budget of a volcano. We first test this hypothesis against the ideal case of Fernandina, Galápagos, where previous models only partly explained the peculiar pattern of circumferential and radial eruptive fissures and the geometry of the intrusions determined by inverting the deformation data. We show that by taking into account the decompression due to the caldera formation, the modeled edifice stress field is consistent with all the observations. We then develop a general model for the stress state at volcanic edifices with calderas based on the competition of caldera decompression, magma buoyancy forces and tectonic stresses. These factors control: 1) the shallow accumulation of magma in stacked sills, consistently with observations; 2) the conditions for the development of circumferential and/or radial eruptive fissures, as observed on active volcanoes. This top-down control exerted by changes in the distribution of mass at the surface allows better understanding of how shallow magma is transferred at active calderas, contributing to forecasting the location and type of opening fissures.

Description: Published

Description: 257-293

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: Highlights -Gas blowouts from water wells are frequent in the southeastern zone of Rome -Emitted gas killed some pets and families had to be evacuated for security reasons -Gas has a magmatic origin with the highest helium R/Ra of Colli Albani gas discharges -Monitoring of soil CO2 flux and air gas concentration allowed to assess gas hazard -Gas diffusing in soil reached nearby houses creating dangerous indoor conditions

Description: The southeastern zone of Rome city is located at the northwest periphery of the quiescent Colli Albano volcano. This zone is characterized by the presence of a shallow (depth ~ 45–50 m) gas pressurized aquifer that produces gas blowouts when it is reached by wells. Three gas blowouts occurred in this zone in 2003, 2008 (another one was discovered during the present study) and 2016 and in this paper we describe in detail the latter two. The emitted gas consists mostly of CO2 (〉90 vol%) and contains a low but significant quantity of H2S (0.3–0.5 vol%) and it has the highest helium isotopic R/Ra value (1.90) of all Colli Albani natural gas discharges, suggesting its likely magmatic origin. In both the described gas blowouts, dozens of families had to be prudentially evacuated from their houses and the emitted gas killed some animals. We monitored, continuously or by discrete surveys, the soil CO2 flux, the indoor and outdoor air concentration of CO2 and H2S, the environmental parameters and we checked whether the cementation of the gas releasing wells had been effective. In both cases, the upper part of the wells had been partly closed with an inflating packer to avoid free gas dispersion in atmosphere; as a consequence gas diffused laterally from the wells into the permeable surficial soil up to reach the nearest houses creating hazardous indoor conditions, particularly for CO2 in some basements. During the well cementation operations, and in one case because of the packer rupture, gas and nebulized water were freely discharged from the wells into the atmosphere, and high air CO2 and H2S concentrations were found. Fortunately gas was quickly dispersed by strong winds. The positive results obtained in all the studied gas blowouts demonstrate that our applied geochemistry approach represents a model of intervention useful for the assessment of the hazard associated to accidental endogenous gas release. This model is of fundamental importance also to overcome the risk problems created by accidental gas blowout from wells in an urbanized environment, up to the safe return of the people in their evacuated houses.

Description: Published

Description: 104769

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: In the world, volcanic systems exhibit a wide range of eruption styles threatening the lives of millions of people. Relatively slow effusive eruptions generate lava flows (low viscosity magma) and lava domes (high viscosity magma) and tend to evolve over days to decades. Alternatively, explosive eruptions can inject very large volumes of fragmented magma and volcanic gas high into the atmosphere over shorter periods (minutes to weeks to months). Mitigation of the associated risk to populations, the built environment, and the cultural heritage relies upon our ability to accurately assess volcanic hazards, and this, in turn, depends on our understanding of the processes that control the style and scale of volcanic eruptions. To this end, technological developments over the last couple of decades have greatly improved our ability to characterize magmatic systems and detect precursors at high spatial and temporal resolution through the use of analytical and observational volcanology, including monitoring-derived data, and volcano geophysics. Numerical modeling of magma ascent can serve to link all of these data and processes to build effective near-real-time strategies. The complexity of the volcanic system, derived from the multiphase, multicomponent character of the magmatic mixtures and from their interaction dynamics with the surrounding host rocks, is however manifested in the complexity of its mathematical representation, and numerical models able to describe several interdependent processes, eventually at disequilibrium conditions, are required to capture the nature of volcanic systems with fidelity. In this chapter, we present the main equations governing magma ascent, highlighting the multiphase and disequilibrium nature of volcanic flows, and the presence of complex feedback mechanisms between gas exsolution, outgassing, and crystallization that are able to influence the most important characteristics of the resulting volcanic events. Then, a suite of numerical simulations is described to show the effect of some parameters and processes in controlling eruption style and scale, and thus the potential eruption hazard.

Description: Published

Description: 239-284

Description: 5V. Processi eruttivi e post-eruttivi

Description: Active lava lakes – as the exposed upper part of magmatic columns – are prime locations to investigate the conduit flow processes operating at active, degassing volcanoes. Persistent lava lakes require a constant influx of heat to sustain a molten state at the Earth's surface. Several mechanisms have been proposed to explain how such heat transfer can operate efficiently. These models make contrasting predictions with respect to the flow dynamics in volcanic conduits and should result in dissimilar volatile emissions at the surface. Here we look at high-frequency SO2 fluxes, plume composition, thermal emissions and aerial video footage from the Villarrica lava lake in order to determine the mechanism sustaining its activity. We found that while fluctuations are apparent in all datasets, none shows a stable periodic behaviour. These observations suggest a continuous influx of volatiles and magma to the Villarrica lava lake. We suggest that ascending volatile-rich and descending degassed magmas are efficiently mixed within the volcanic conduit, resulting in no clear periodic oscillations in the plume composition and flux. We compare our findings to those of other lava lakes where equivalent gas emission time-series have been acquired, and suggest that gas flux, magma viscosity and conduit geometry are key parameters determining which flow mechanism operates in a given volcanic conduit. The range of conduit flow regimes inferred from the few studied lava lakes gives a glimpse of the potentially wide spectrum of conduit flow dynamics operating at active volcanoes.

Description: This research was conducted as part of the “Trail By Fire” expedition (PI: Y. Moussallam). The project was supported by the Royal Geographical Society (with the Institute of British Geographers) with the Land Rover Bursary; the Deep Carbon Observatory DECADE Initiative; Ocean Optics; Crowcon; Air Liquide; Thermo Fisher Scientific; Santander; Cactus Outdoor; Turbo Ace and Team Black Sheep. We thank Sebastien Carretier and Rose-Marie Ojeda together with IRD South-America personnel for all their logistical help. We further thank the CONAF and DGAC for their help. YM acknowledges support from the Scripps Institution of Oceanography Postdoctoral Fellowship program. CIS acknowledges a research startup grant from Victoria University of Wellington

Description: Published

Description: 237-247

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: In this paper a new approach for processing arrays of data is proposed. It is based on fuzzy logic and the concepts of cellular computation. Arrays of simple, identical processing elements (called fuzzy cells) are defined by using fuzzy rules. Moreover, each fuzzy cell interacts with its local neighbors. The overall behavior of these locally interacting fuzzy systems is used to process arrays of data. Some examples of practical applications are proposed. Among these, the new approach is applied to image-processing problems, and to the simulation of heat diffusion phenomena.

Description: This work was partially supported by the Italian National Research Council (C.N.R.) under the special project "Reti neurali per i sistemi di controllo".

Description: Published

Description: 47-52

Description: 3IT. Calcolo scientifico

Description: JCR Journal

Description: A review of seismic methods for monitoring and understanding active volcanoes

Description: Published

Description: 4V. Processi pre-eruttivi

Description: Recent measurements of surface vertical displacements of the European Alps show a correlation between vertical velocities and topographic features, with widespread uplift at rates of up to ~2–2.5 mm/a in the North-Western and Central Alps, and ~1 mm/a across a continuous region from the Eastern to the South-Western Alps. Such a rock uplift rate pattern is at odds with the horizontal velocity eld, characterized by shortening and crustal thickening in the Eastern Alps and very limited deformation in the Central and Western Alps. Proposed me- chanisms of rock uplift rate include isostatic response to the last deglaciation, long-term erosion, detachment of the Western Alpine slab, as well as lithospheric and surface de ection due to mantle convection. Here, we assess previous work and present new estimates of the contributions from these mechanisms. Given the large range of model estimates, the isostatic adjustment to deglaciation and erosion are su cient to explain the full observed rate of uplift in the Eastern Alps, which, if correct, would preclude a contribution from horizontal shortening and crustal thickening. Alternatively, uplift is a partitioned response to a range of mechanisms. In the Central and Western Alps, the lithospheric adjustment to deglaciation and erosion likely accounts for roughly half of the rock uplift rate, which points to a noticeable contribution by mantle-related processes such as detachment of the European slab and/or asthenospheric upwelling. While it is di cult to independently constrain the patterns and magnitude of mantle contributions to ongoing Alpine vertical displacements at present, future data should provide additional insights. Regardless, interacting tectonic and surface mass redistribution processes, rather than an individual forcing, best explain ongoing Alpine elevation changes.

Description: Published

Description: 589-604

Description: 1T. Struttura della Terra

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: We report on the Strombolian to Violent Strombolian eruption of Montaña Grande which occurred between 789 and 725 BCE in the Güimar Valley on the NE flank of Tenerife island. The eruption produced a ca. 180 m-high sco- ria cone, a thick fallout deposit mostly dispersed southwest and a vast lava flow field that extends east of the cone, towards the coast, for 3.3 × 2.2 km. The eruption occurred in an unusual geodynamic context, outside the North West Rift and North East Rift zones and out of Las Cañadas caldera which are the main geological structures of Tenerife, where the volcanic activity concentrated during the Holocene. The tephra and lava have a trachybasalt composition similar to products of the recent activity of Tenerife but characterized by a distinct trace element pattern (Ta depletion relative to Nb), that points to a distinct source for the magma feeding the eruption and an ascent history along the whole crust which is independent and different from the central feeding system of the Teide-Pico Viejo volcanic complex. The study of this eruption, which until now had been completely neglected, adds new significant data for the correct definition of volcanic risk in Tenerife.

Description: Published

Description: 106918

Description: 1V. Storia eruttiva

Description: JCR Journal

Description: Between February 6 and 12, 2016, an earthquake sequence affected the western sector of the Hyblean foreland domain in SE Sicily (Italy), a region characterized by several disastrous events, as the seismic history describes, of which little is still known about the seismogenic sources. Despite the low magnitude of most events (MLmax 4.3), the sequence represents one of the largest episodes of seismic strain release in the area over the last 30 years since the December 13, 1990 earthquake (ML = 5.4). Accurate seismic phase arrival times related to the seismic sequence were obtained by using a wave-correlation method which enabled a significant improvement in precision of earthquake locations, allowing to detect a N-S striking rupture area about 8 km deep. The N-S trending discontinuity well matches, in the near-surface, with the observed geological structures, in rather good agreement with the computed focal solutions which evidence a roughly N-S elongated structure characterized by a left-lateral kinematics. The detailed knowledge learned on the geometry of the fault surface activated by the seismic sequence, together with the characterization of earthquake source parameters, gave important constraints for a realistic estimation of seismic ground motion throughout stochastic simulations. The modeling technique was based on the comparison between instrumental signals of the strongest event of the sequence and the associated synthetic ones. This permitted to properly define the set of input parameters for the construction of a realistic scenario for a MW 6.1 earthquake, which provides the largest contribution to the seismic hazard for the investigated area.

Description: Published

Description: 106553

Description: 4T. Sismicità dell'Italia

Description: JCR Journal

Description: Following on the discovery (in 2011) of a layer of distal tephra from the Pomici di Avellino eruption (Somma-Vesuvius, EU5) in the Agro Pontino (southern Lazio, Italy), further detailed study of the Holocene sediment archives in this graben and in the nearby Fondi coastal basin showed that distal tephra from this EU5 eruption occurs as a rather continuous, conspicuous layer. Two other, less conspicuous tephra layers were found, identified as the earlier Astroni 6 eruption from the Campi Flegrei (Fondi basin) and the later AP2 eruption of the Somma-Vesuvius (Agro Pontino). The identification of the distal tephra layers rests upon a combination of criteria, including stratigraphy, macro characteristics, mineralogy, geochemical data on glass composition, Sr-isotopic ratios, and the known tephrochronology for the period concerned, i.e. between c. 2500 and 1000 BCE. 14C datings serve to constrain their age. No significant spatial variation in the characteristics of the main tephra layer (EU5) was observed, other than distinct fining with increasing distance from the vent. Based on a detailed palaeogeographical reconstruction, the occurrence and preservation of these tephra are explained by the local environmental conditions governing their preservation during this time span (the Central Italian Bronze Age), and by the later evolution of the area. The observations underpin that multiple corings are needed to fully assess whether sedimentary hiatuses exist in palaeorecords, based on cores from sediment archives. Lastly, our study shows that hazard evaluations for future eruptions by Campanian volcanoes should pay more attention to their potential impacts on distal areas.

Description: Published

Description: 107041

Description: 1V. Storia eruttiva

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: The Pleistocene (~460–265 ka) San Venanzo volcanic complex belongs to the IAP (Intra-Apennine Province) in central Italy, which comprises at least four small Pleistocene monogenetic volcanoes plus several unrooted pyroclastic deposits with peculiar mineralogical and whole-rock chemical compositions. San Venanzo products are strongly SiO2-undersaturated, CaO- and MgO-rich and show ultrapotassic serial character. The relatively common occurrence of calcite in the pyroclastic rocks and the overall high CaO content are interpreted in literature as primary mineral. The main rock facies at San Venanzo are calcite-rich scoria and lapilli tuffs, with minor massive lava flows, and a rare pegmatoid variant (melilitolitic pockets). All the San Venanzo rocks are feldspar-free, with a typical paragenesis of forsteritic olivine, non-stoichiometric Ca-rich diopside, melilite, leucite, kalsilite, opaque minerals, nepheline, phlogopite, calcite, apatite, cuspidine, wollastonite, kirschsteinite-monticellite s.s. ± glass and other minor and very rare minerals typical of agpaitic melts. Based on petrographic analyses, the studied rocks can be classified as olivine melilitites, olivine leucite melilitites, venanzites (a local variant of kamafugites), calcite leucite melilitolites and Ca-rich olivine leucite melilitite tuffs. Mass balance calculations indicate a direct genetic link between the lava bodies and the pegmatoid melilitolitic pocket through a fractional crystallization process characterized by the removal of ~74% of a melilite-bearing uganditic cumulate made up of melilite, leucite, olivine, kalsilite and chromite. Primitive mantle-normalized patterns of the lavas and tuffs are rather spiked and share negative anomalies for Ba, Nb, Ta, P and Ti resembling typical magmas generated by supra-subduction mantle wedge. These compositions are very different from the only two other kamafugite localities outside Italy (Toro Ankole and Virunga in the East Africa Rift and Alto Paranaiba Igneous Province in SE Brazil). The melilitolite sample is more incompatible element-enriched than the other San Venanzo volcanic rocks, coherently with its evolved liquid composition proposed here. Major and trace element contents indicate a general depletion proportional to the amount of CaO content. The negative trends in Harker-type diagrams with CaO as abscissa are compatible with a process of variable interaction between a silicate magma with sedimentary marly carbonates/limestones. The presence of Mg-rich (Fo97–92) and rim-ward CaO-enriched (up to 1.72 wt%) euhedral olivine, as well as the presence of thin kirschsteinite rim around olivine crystals agree with a process of crustal carbonate assimilation by an originally strongly SiO2-undersaturated silicate magma. On the other hand, the lack of feldspars even in the rocks with the highest SiO2, the high CaO content, and the extreme SiO2-undersaturation of San Venanzo rocks exclude their derivation from a simple peridotitic source. In order to generate these peculiar compositions, the presence of a SiO2-K2O-CaO-rich H2O-bearing component, identified in a carbonated phlogopite peridotite is required. The results of different isotopic systematics (Sr-Nd-Pb-He-Ne-Ar) presented here are compatible with a process of crustal contamination both at mantle source levels (to explain the general N-S isotopic trends recorded in Quaternary volcanic rocks of Italian peninsula and Sicily) and with interaction of ultrabasic melts with limestones at shallow crustal depths.

Description: Published

Description: 103256

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: The chemical and isotopic features of the fluids (water and gases) in the Lucane thermal area (southern Italy) have been investigated in order to verify their origin, water temperature in the geothermal reservoir, and to recognize the main natural processes concerning the water composition during ascent towards the surface. The Lucane geothermal system is placed in the southern sector of the Apennines chains, a seismically active area, close to the southern base of the Mt. Alpi carbonate massif. Along the study area, two main sets of high-angle faults form an almost orthogonal fault system that, as suggested by local structural geology, acts as a preferential pathway for uprising deep fluids. Here, we recognized two different types of waters: (i) cold shallow waters having a meteoritic origin and interacting with carbonate rocks (dolomite and calcite), whose dissolved gases show a dominant atmospheric contribution and (ii) hypothermal waters (average temperature of 21 °C), having a meteoritic origin and interacting with both carbonate rocks and inter-bedded evaporitic deposit. Geochemical data allow estimating a geothermal reservoir temperature between 30 °C and 60 °C, according to silica and Ca/ Mg geothermometers, respectively. A heat discharge related to hypothermal groundwater flow between 7.75E +06 and 2.00E+07 J/s was computed. δ18O and δ2Η data allowed recognizing a meteoric origin for hypothermal (hereafter TL) waters, with mean recharge (infiltration) elevations between 1300 and 1700 m a.s.l. These waters are gas-rich (e.g., CO2 and He), which amounts are higher than those in air-saturated water (ASW). Carbon and helium isotope signature in the TL waters indicate their mainly crustal origin and involve a tectonic control on fluid migration through the crust. Furthermore, we observe that the He isotopic signature in gases dissolved in TL waters is stable over time and its monitoring could be a powerful tool to assess the seismogenetic processes since their preparatory phases.

Description: Published

Description: 106618

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: Individual volcanoes can produce both effusive and explosive eruptions. A transition between these two eruption styles dramatically changes the hazards and can occur either between distinct eruption events or within one eruption episode. The causes of these transitions are difficult to determine due to the number of system parameters that can influence whether or not magma fragments in a runaway process. We apply a numerical model of magma ascent in a volcanic conduit to isolate and test the effects of key parameters related to magma rheology and system geometry. We find that for a given volcanic system, parameters that control magma viscosity, such as initial water mass fraction, initial crystal volume fraction, and temperature, have the greatest influence on whether or not magma fragments during ascent and erupts explosively. We also define a ‘critical condition’ for the full set of initial parameters under which a transition in eruption style, from effusive to explosive or the reverse, is more likely to occur. Under these conditions, small heterogeneities in the water or crystal content of the magma, or small perturbations to the conduit pressure gradient due to magma chamber overpressure or dome growth or collapse, can disrupt the magmatic conditions and cause a transition in eruption style. The 2010 VEI 4 eruption of Merapi Volcano included both effusive and explosive phases and was larger by an order of magnitude than its eruptions during the previous century. We constrain our model for the Merapi system using published literature values and show that between the previous eruption in 2006 and the 2010 eruption, the shallow magmatic system at Merapi reached critical conditions due to the ascent from depth of a large, hotter, more volatile-rich magma. Under these critical conditions and according to our model results, small changes in the volatile content of the magma, small dome collapses, subtle changes in degassing rate, or the addition of CO2 to the magma through decarbonation of the bedrock, are all feasible mechanisms for triggering rapid transitions between effusive and explosive activity during the 2010 eruption period.

Description: Published

Description: 106767

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Inspired by coarea formula in geometric measure theory, an occupation time formula for continuous semimartingales in R^N is proven. The occupation measure of a semimartingale, for N ≥ 2, is singular with respect to Lebesgue measure but it has a bounded density “transversal” to a foliation, under proper assumptions. In the particular case of the foliation given locally by the distance function from a manifold, the transversal density is related to a geometric local time of the semimartingale at the manifolds of the foliation.

Description: Published

Description: 3342–3361

Description: 3IT. Calcolo scientifico

Description: JCR Journal

Description: Magma-carbonate interactions and the subsequent CO2 release can occur before and during an eruption, critically affecting magma storage and ascent processes. However, the mechanisms and timescales of those interactions are unclear, particularly during the fast magma withdrawal that feeds high-intensity eruptions. In order to better understand magma‑carbonate interactions, we selected the caldera-forming Pomici di Base plinian eruption, the oldest (22 ka) and largest (〉 4.4 km3) explosive event in the history of the Somma-Vesuvius volcanic system, as case study. During this event the emission of trachytic and latitic-shoshonitic (~25% and ~75% of the erupted magma volume respectively) magmas generated a long-lasting plinian column, hypothetically driven by CO2 liberation during magma‑carbonate interaction. In this study, we reconstruct in detail the evolution of the plumbing system during the Pomici di Base eruption combining geochemical (major/minor elements and radiogenic/stable isotopes) analyses of juvenile products with thermodynamic and kinetic calculations. Our results demonstrate that magmatic stoping (i.e., the formation and transport of host-rock pieces into a magma body) during caldera collapse evolution can promote rapid magma assimilation of carbonate blocks and CO2-rich fluids resulting from destabilization of the carbonate bedrock, thus triggering CO2 release and acting as a fuel for the eruption explosivity, especially when residual hot mafic magmas are involved. Our findings suggest that the accurate knowledge of these processes and their influence on eruptive dynamics are critical for improving the hazard assessments of volcanoes with plumbing systems located in carbonate bedrocks.

Description: Published

Description: 105628

Description: 1V. Storia eruttiva

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: 4V. Processi pre-eruttivi

Description: 5V. Processi eruttivi e post-eruttivi

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Tectonic earthquake swarms (TES) often coincide with aseismic slip and sometimes precede damaging earthquakes. In spite of recent progress in understanding the significance and properties of TES at plate boundaries, their mechanics and scaling are still largely uncertain. Here we evaluate several TES that occurred during the past 20 years on a transform plate boundary in North Iceland. We show that the swarms complement each other spatially with later swarms discouraged from fault segments activated by earlier swarms, which suggests efficient strain release and aseismic slip. The fault area illuminated by earthquakes during swarms may be more representative of the total moment release than the cumulative moment of the swarm earthquakes. We use these findings and other published results from a variety oftectonic settings to discuss general scaling properties for TES. The results indicate that the importance of TES in releasing tectonic strain at plate boundaries may have been underestimated.

Description: Published

Description: 62-70

Description: 3T. Sorgente sismica

Description: JCR Journal

Description: Hekla is a frequently active volcano with an infamously short pre-eruptive warning period. Our project contributes to the ongoing work on improving Hekla’s monitoring and early warning systems. In 2012 we began monitoring gas release at Hekla. The dataset comprises semi-permanent near-real time measurements with a MultiGAS system, quantification of diffuse gas flux, and direct samples analysed for composition and isotopes (δ13C, δD and δ18O). In addition, we used reaction path modelling to derive information on the origin and reaction pathways of the gas emissions. Hekla’s quiescent gas composition was CO2-dominated (0.8 mol fraction) and the δ13C signature was consistent with published values for Icelandic magmas. The gas is poor in H2O and S compared to hydrothermal manifestations and syn-eruptive emissions from other active volcanic systems in Iceland. The total CO2 flux from Hekla central volcano (diffuse soil emissions) is at least 44 T d−1, thereof 14 T d−1 are sourced from a small area at the volcano’s summit. There was no detectable gas flux at other craters, even though some of them had higher ground temperatures and had erupted more recently. Our measurements are consistent with a magma reservoir at depth coupled with a shallow dike beneath the summit. In the current quiescent state, the composition of the exsolved gas is substantially modified along its pathway to the surface through cooling and interaction with wall-rock and groundwater. The modification involves both significant H2O condensation and scrubbing of S-bearing species, leading to a CO2-dominated gas emitted at the summit. We conclude that a compositional shift towards more S- and H2O-rich gas compositions if measured in the future by the permanent MultiGAS station should be viewed as sign of imminent volcanic unrest on Hekla.

Description: The research leading to these results has received funding from the Icelandic Centre for Research (RANNIS, grant number 110002-0031); the European Community’s Seventh Framework Programme under Grant Agreement No. 308377 (Project FUTUREVOLC); and the International Civil Aviation Organization.

Description: Published

Description: 80-99

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: The tectonic evolution of the European Eastern Alps within the Alpine orogeny is still under debate. Open ques- tions include: the link between surface, crustal and mantle structures; the nature of the Moho gap between the two plates; the relationship between the Alps, the adjacent foreland basin and the Bohemian Massif lithospheric blocks. We collected one year of continuous data recorded by ~250 broadband seismic stations –55 of which installed within the EASI AlpArray complementary experiment– in the Eastern Alpine region. Exploiting surface wave group velocity from seismic ambient noise, we obtained an high-resolution 3D S-wave crustal model of the area. The Rayleigh-wave group-velocity from 3 s to 35 s are inverted to obtain 2-D group velocity maps with a resolution of ~15 km. From these maps, we determine a set of 1D velocity models via a Neighborhood Algorithm, resulting in a new 3D model of S-wave velocity with associated uncertainties. The vertical parameterization is a 3-layer crust with the velocity properties in each layer described by a gradient. Our final model finds high correlation with specific geological features in the Eastern Alps up to 20 km depth, the deep structure of the Molasse basin and important variations of crustal thickness and velocities as a result of the Alpine orogeny post-collisional evolution. The strength of our new information relies on the absolute S-wave crustal velocity and the velocity gradient unambiguously sampled along the Moho, only limited by the amount and quality distribution of the data available.

Description: Published

Description: 100006

Description: 1T. Struttura della Terra

Description: 2TR. Ricostruzione e modellazione della struttura crostale

Description: N/A or not JCR

Description: The Torre Alfina medium enthalpy geothermal field is located about 10 km north of the Bolsena caldera (Italy). The reservoir is a buried structural high consisting of fractured Meso-Cenozoic carbonate sequences and sealed by clayey flysch successions and Pliocene marine clays. We performed TOUGH2 numerical simulations, testing different model designs based on contrasting conceptual models. Results indicate that deep circulation is forced by the geometry of the reservoir and by the applied T and P gradients. We interpret the Torre Alfina field as a "blind" system, mostly recharged by lateral advection of heat and fluids from the Bolsena caldera deep high-enthalpy system, through the permeable caldera faults.

Description: Published

Description: 101947

Description: 1TR. Georisorse

Description: 6SR VULCANI – Servizi e ricerca per la società

Description: 7SR AMBIENTE – Servizi e ricerca per la società

Description: JCR Journal

Description: Soil gas and Electrical Resistivity Tomography (ERT) surveys were performed in Medolla (Emilia-Romagna Region, northern Italy) within a farming area characterized by macroseeps, absence of vegetation and anomalous temperatures of soil to investigate the soil gas migration mechanism and verify the presence of a buried fault intersecting the macroseeps. Soil gas (222Rn, 220Rn, He and C2H6) concentrations and flux (φCO2 and φCH4) measurements were carried out from 2008 to 2015, comprising the 2012 Emilia seismic sequence. Moreover, in 2016 a ERT survey, combined with new flux measurements, was performed along four profiles (ranging from 180 to 630 m long) centered on the main macroseep. We found that the seismic sequence sensibly influenced the soil gas distribution in the area. All investigated species, but He, increased their values early after the mainshocks, likely due to crustal deformation which promoted the geogas uprising. In 2015, when the stress has vanished, these concentrations gradually decreased toward pre-seismic values. Helium concentrations showed an opposite behavior as they decreased in May 2012 and then gradually increased over time. This trend may be reasonably due to the enhancement of the strain field which promoted the He dissipation from soil to the atmosphere, due to its high volatility. In all the geochemical surveys conducted from 2008 to 2015, soil gas high values around the main macroseeps were identified, delighting the presence of an alignment in the E-W direction. This trend, identified for several gas species, ultimately supports the theory of a hidden fault which favors the intensification of fluids migration along zones characterized by greater permeability. ERT results highlighted a sub-horizontal layering characterized by different resistivity intervals, roughly matching local stratigraphy. In most profiles we observed a slightly increase of resistivity and a sharp inter-ruption of the electro-layering in correspondence of the main macroseep, both near the surface and at depth. This implies that a fracture zone due to the presence of a buried fault cannot be excluded. The combined use of geochemical and geophysical techniques in this study confirmed the usefulness of such multiparametric approach for mapping out hidden structures in tectonically active areas, allowing to better understanding the fluid migration processes through preferential leakage pathways.

Description: Published

Description: 106678

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: 7A. Geofisica per il monitoraggio ambientale

Description: JCR Journal

Description: We present geochemical data collected from volcanic ash-bearing sediments on the upper slope of the northern Hikurangi margin during the RV SONNE SO247 expedition in 2016. Gravity coring and seafloor drilling with the MARUM-MeBo200 allowed for collection of sediments down to 105 meters below seafloor (mbsf). Release of dissolved Sr2+with isotopic composition enriched in 86Sr (87Sr/86Sr minimum = 0.708461 at 83.5 mbsf) is indicative of ash alteration. This reaction releases other cations in the 30-70 mbsf depth interval as reflected by maxima in pore-water Ca2+and Ba2+concentrations. In addition, we posit that Fe(III) in volcanogenic glass serves as an electron acceptor for methane oxidation, a reaction that releases Fe2+measured in the pore fluids to a maximum concentration of 184 μM. Several lines of evidence support our proposed coupling of ash alteration with Fe-mediated anaerobic oxidation of methane (Fe-AOM) beneath the sulfate-methane transition (SMT), which lies at ∼7 mbsf at this site. In the ∼30-70 mbsf interval, we observe a concurrent increase in Fe2+and a depletion of CH4with a well-defined decrease in δ13C-CH4values indicative of microbial fractionation of carbon. The negative excursions in δ13C values of both DIC and CH4are similar to that observed by sulfate-driven AOM at low SO2−4concentrations, and can only be explained by the microbially-mediated carbon isotope equilibration between CH4and DIC. Mass balance considerations reveal that the iron cycled through the coupled ash alteration and AOM reactions is consumed as authigenic Fe-bearing minerals. This iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals, as estimated from sequential extraction analyses. Using a numerical modeling approach we estimate the rate of Fe-AOM to be on the order of 0.4μmol cm−2yr−1, which accounts for ∼12% of total CH4removal in the sediments. Although not without uncertainties, the results presented reveal that Fe-AOM in ash-bearing sediments is significantly lower than the sulfate-driven CH4consumption, which at this site is 3.0μmol cm−2yr−1. We highlight that Fe(III) in ash can potentially serve as an electron acceptor for methane oxidation in sulfate-depleted settings. This is relevant to our understanding of C-Fe cycling in the methanic zone that typically underlies the SMT and could be important in supporting the deep biosphere.

Description: Gymnodinium catenatum is able to produce paralytic shellfish toxins (PSTs) and was responsible for a massive bloom in the Taiwan Strait, East China Sea, in June 2017, which resulted in serious human poisoning and economic losses. To understand the origin of the bloom and determine the potential for blooms in subsequent years, water and sediment samples collected in the Taiwan Strait from 2016 to 2019 were analyzed for cells and cysts using light microscopy (LM) and/or quantitative polymerase chain reaction (qPCR). The morphology of both cells and cysts from the field and cultures was examined with LM and scanning electron microscopy (SEM). Large subunit (LSU) and/or internal transcribed spacer (ITS)-5.8S rRNA gene sequences were obtained in 13 isolates from bloom samples and five strains from cysts. In addition, cells of strains TIO523 and GCLY02 (from the Taiwan Strait and Yellow Sea of China, respectively) were subjected to growth experiments, and cysts from the field were used for germination experiments under various temperatures. Our strains shared identical LSU and ITS-5.8S rRNA gene sequences with those from other parts of the world, and therefore belonged to a global population. A low abundance of G. catenatum cells were detected during most of the sampling period, but a small bloom was encountered in Quanzhou on June 8, 2018. Few cysts were observed in 2016 but a marked increase was observed after the bloom in 2017, with a highest density of 689 cysts cm−3. Cysts germinated at temperatures between 14 and 23 °C with a final germination rate over 93%. Strains TIO523 and GCLY02 displayed growth at temperatures between 17 and 26 °C and 14 and 26 °C, respectively, with both strains displaying the highest growth rate of ca. 0.5 divisions d–1 at 23 °C. The PSTs of the three strains and cysts from the sediments were analyzed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). All strains were able to produce PSTs, which were dominated by N-sulfocarbamoyl C toxins (C1/2, 53.0–143.5 pg cell−1) and decarbamoyl gonyautoxins (dcGTX2/3, 26.7–52.1 pg cell−1), although they were not detected in cysts. However, hydroxybenzoyl (GC) toxins were detected in both cells and cysts. Our results suggested that the population in the Taiwan Strait belonged to a warm water ecotype and has a unique toxin profile. Our results also suggested that the persistence of cells in the water column may have initiated the bloom.

Description: Reconstruction maps and map sequences provide the essential basis and boundary conditions for interpreting ancient Earth system processes. Such maps can be generated using a variety of techniques to reunite formerly conjugate features as interpreted in a range of different data types. The highest confidence is achieved by reuniting large numbers of geographically widespread and precisely located markers that are simply and robustly interpreted. These markers are most widespread in the oceanic lithosphere, because of its relatively simple tectonic history of plate divergence that ends with subduction. The reliability of maps decreases with time in the past as the distribution of markers is first confined to the continental crust and, before this, to geographically ever-smaller and geologically more interpretation-dependent remnants, alongside which the range of suitable reconstruction techniques narrows. Relative reconstructions must be placed in a global reference frame, using any of a variety of techniques that also become smaller with past time. Reconstructions have been used for paleogeographic mapping to provide constraints on studies of regional deformation and to provide constraints on plate motion for geodynamic studies.

Description: The enigmatic 85°E Ridge crosses the Bay of Bengal from north to south. Its strong gravity anomaly low is associated with Cretaceous hotspot volcanism. South of 5°N, the gravity low bends into a SW-NE orientation and continues as far SW as the Afanasy Nikitin Seamounts. This change has been interpreted to represent a bent hotspot track. We report new constraints on the crustal structure and genesis beneath the SW-trending gravity low based on new refraction seismic, reflection seismic, and shipborne gravity data. Our findings show that the crustal structure across the gravity low does not differ significantly from the adjacent, 4.5 to 7 km thick oceanic crust. No basement ridge, significant crustal thickening, or magmatic underplating were identified. We found no evidence for a southern prolongation of the 85°E Ridge. Instead, our P-wave velocity and density models reveal the gravity low to express a flexural basin, which is a result of widespread mid-Miocene to recent lithospheric deformation in the Indian Ocean. The ~25 mGal negative gravity anomaly is therefore not related to the passage of the Indian plate over a mantle plume, casting doubt on the possibility that volcanism at the Afanasy Nikitin Seamounts might be related to the same plume as the northern 85°E Ridge. The northern 85°E Ridge may have been generated at the northern prolongation of the 86°E Fracture Zone.

Description: Greenhouse gas emissions from physical permafrost thaw disturbance and subsidence, including the formation and expansion of thermokarst (thaw) lakes, may double the magnitude of the permafrost carbon feedback this century. These processes are not accounted for in current global climate models. Thermokarst lakes, in particular, have been shown to be hotspots for emissions of methane (CH4), a potent greenhouse gas with 32 times more global warming potential than carbon dioxide (CO2) over a 100-year timescale. Here, we synthesize several studies examining CH4 dynamics in a representative first-generation thermokarst lake (Vault Lake, informal name) to show that CH4 production and oxidation potentials vary with depth in thawed sediments beneath the lake. This variation leads to depth-dependent differences in both in situ dissolved CO2:CH4 ratios and net CH4 production responses to additional warming. Comparing CH4 production, oxidation, and flux values from studies at Vault Lake suggests up to 99% of produced CH4 is oxidized and/or periodically entrapped before entering the atmosphere. We summarize these findings in the context of CH4 literature from thermokarst lakes and identify future research directions for incorporating thermokarst lake CH4 dynamics into estimates of the permafrost carbon feedback.

Description: Grain size reduction due to cataclasis is a key process controlling fault frictional properties during the seismic cycle. We investigated the role of cleavage planes on fracturing and microstructural evolution during cataclasis in wet and dry carbonate fault gouges (50 wt% calcite, 50 wt% dolomite) deformed in a rotary-shear apparatus over a wide range of slip rates (30 μms−1 to 1 ms−1) and displacements (0.05–0.4 m). During shearing, progressive strain localization forms a narrow slip zone that undergoes significant frictional heating (at high slip rates), but the bulk gouge always accommodates low finite shear strains and deforms at low temperatures. Microstructural analysis of the bulk gouges indicates that deformation occurred by brittle fracturing and twinning. Microfractures in calcite are closely spaced, often exploit cleavage r-rhomb planes, and occur mainly subparallel to the expected principal stress orientation (σ1). Instead, twin planes typically occur sub-perpendicular to σ1. Electron backscatter diffraction analysis of the bulk gouges shows that calcite develops a well-defined crystallographic preferred orientation (CPO) at all investigated deformation conditions. The CPO is defined by a clustering of the calcite c-axes around an orientation sub-parallel to σ1. The calcite CPO is interpreted to result from grain rotation during granular flow, followed by brittle fracturing that occurred preferentially along calcite cleavage planes. This interpretation is supported by measurements of calcite grain shape-preferred orientations that show a population of elongate calcite grains oriented with their long axes sub-parallel to σ1. Our experimental results indicate that well-defined CPOs can form at low temperature in cataclastic fault rocks, and that mineral cleavage can strongly influence the evolution of grain sizes and shapes during comminution.

Description: Published

Description: 37-50

Description: 3T. Sorgente sismica

Description: 2IT. Laboratori analitici e sperimentali

Description: JCR Journal

Description: An update of the surface ground deformation field over the Lipari-Vulcano complex has been provided by analyzing all the available GPS observations collected in the last two decades. The geodetic velocity field, referred to a fixed Eurasian frame, shows a remarkable negative velocity gradient between the southernmost stations (velocity values of ∼9.0 mm/yr) and the northernmost ones, resulting in a N–S contraction of ∼4.5 mm/yr. In addition, all the GPS stations show subsidence with rates decreasing from the northernmost stations (∼ -10.0 mm/yr) to the southernmost ones (∼ -4.8 mm/yr). Modelling of geodetic data demonstrates that the observed surface deformation field results from the joint contribution of regional (tectonic) and local (magmatic) sources. Such a dataset is unable to uniquely constrain the magmatic source. Indeed, the three performed models (M1, M2 and M3) produce statistically equivalent deformation sources. The source modeled in M1 is spatially coincident with that of M3, and both are located beneath the Vulcanello cone at depth of ∼4 km bsl. Conversely, the source modeled in M2 is placed at depth of 0.76 km bsl beneath the northern rim of the La Fossa crater. Integration of these results with geochemical and petrological data already available from literature suggests, however, that the M1≡M3 source placed beneath the Vulcanello cone should be the preferred model.

Description: Published

Description: 106689

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: Turrialba is an active volcano of the Cordillera Volcánica Central in Costa Rica, which is currently experiencing a renewal of the eruptive activity after ~150 years of eruptive quiescence. Because of its explosive eruptive records in the recent geological history and the proximity with the metropolitan area of San José, this volcano poses serious threats to the population and economy of the area. In this study, we investigated the andesitic products of an explosive event (VEI 4) that occurred at Turrialba volcano ~2 ka, which we referred to as “El Retiro” eruption. Results fromfield observations, textural and chemical analyses indicate that the El Retiro eruptionwas characterized by two main pulses separated by a low energy activity. The eruption was fed by a homogeneous andesitic magma batch that crystallized along a P-T path of 0.1–400 MPa and 1050–1145 °C. The vesicle number density of pumiceous clasts ranges between 107 and 108 cm−3, in agreement with previous data from subplinian eruptions. The magma batch underwent decompression rates and pre-fragmentation velocities of 0.40–0.95 MPa s−1 and 23–37 m s−1, respectively. A marked textural variability within each stratigraphic layer has been also observed. This potentially suggests a horizontal zonation of the magma column, a condition that may have induced velocity gradients and high viscosity contrasts in the conduit leading to magma fragmentation. The observed pulsating behavior translates into mass eruption rate fluctuations that can be related to changes in magma volatile contents. Further explosive eruptions with characteristics similar to those observed for El Retiro, cannot be excluded at Turrialba volcano. This denotes the importance of investigating eruption dynamics at the conduit, providing key information to rigorously assess the volcanic risk in populated areas.

Description: Published

Description: 101-115

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Reconstruction of Paleomagnetic Secular Variation (PSV) of the geomagnetic field is fundamental both to assess geodynamo models and to obtain age constraints for rocks, sediments and archaeological material. We present refined age-calibrated Holocene PSV and relative paleointensity (RPI) stack curves derived from Arctic marine sediments (Northwestern Barents Sea). The Holocene sections of four sedimentary cores were correlated on the basis of paleomagnetic trends and age models, and stacked. The resultant composite PSV and RPI Holocene records (NBS stack) and the reconstructed Holocene Virtual Geomag- netic Pole (VGP) path were evaluated in comparison with the most recent paleomagnetic stack curves and geomagnetic field models. The data indicate that during the Holocene time, the VGPs moved within the superficial projection of the inner core tangent cylinder, with the exception of short time intervals around 5600 and 3200 cal yr BP when VGPs extended to lower latitudes. These deviations might reflect regional geomagnetic features, such as persistent geomagnetic flux lobes at core-mantle boundary. Our data confirm that the large VGP shift observed around 5600 cal yr BP is the result of an increased radial magnetic field at the core-mantle boundary over North America, whilst the VGP shift around 3200 cal yr BP represents a major swing to middle latitudes toward the Middle East and might be associated to a regional high paleointensity peak, known as Levantine Iron Age Anomaly (LIAA).

Description: Published

Description: 106133

Description: 1A. Geomagnetismo e Paleomagnetismo

Description: JCR Journal

Description: The western limb of the Hellenic Arc defines the boundary of a large intracontinental active extensional domain covering the Aegean and the southwestern part of the Balkan peninsula. Along this boundary a transition from collision in the north to subduction in the south is associated with post-Miocene clockwise rotations of . We present a new GPS velocity field that, with new permanent station velocities in Albania, Bulgaria, Kosovo, Montenegro, and Northern Macedonia, provides insights into previously unresolved aspects on the large-scale dynamics of continental lithosphere and on the relation between long and short-term kinematics. In particular we address (1) the kinematic description of the collision/subduction transition, (2) the relation between long-term finite rotations with geodetically-measured instantaneous rotations, (3) the forces maintaining and resisting the deformation of the extensional domain and (4) the extent of its northern boundary. We use the analogy of rigid elongate inclusions in the velocity field to predict the senses and approximate rates of rotation of crustal blocks in the deforming continental region. Across the collision/subduction transition zone a large rotational pattern in the velocity field is found whose spatial pattern and sense of rotation is compatible with the observed paleomagnetic rotations through the occurrence of fault-bounded block rotations. Geodetic observations show that clockwise vertical axis rotation of the western limb of the Hellenic margin is active today, with distribution and rates that are essentially the same as that defined by the paleomagnetic data for the last 5 Ma. The maximum rates of the rotational component of the velocity field is found along the wide arrangement of fault-bounded blocks in central Greece that accomodate the NE-SW dextral shear transferred from the northern Aegan trough. The northern limit of the rotating margin defines a hinge (Scutari-Pec transverse zone) that has remained stationary throughout the Middle Miocene (relative to the upper plate of the collision/subduction system) with important implications for the distribution of strength of the western margin of the Hellenic Arc. The distribution and style of deformation along the western boundary of the extensional domain is controlled by the relation between gravitational forces, driving the flow of crustal material towards the low-lying adjacent regions sea floor, and heterogeneous resistive forces along the collision/subduction boundary.

Description: Published

Description: 116246

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: Explosive volcanic eruptions are characterized by highly variable degrees of magma fragmentation, even during a single eruptive event. The increasing amount of fine pyroclasts is often uncritically related to explosive magma–water interaction (i.e., hydromagmatic fragmentation). Here we report examination of two examples of major explosive eruptions from the Quaternary Vulsini Volcanic District (central Italy), in which the fine-grained nature of deposits, even in near-vent settings, indicates negligible effect of transport and implies the eruption of highly fragmented magmas. SEM morphoscopy of the juvenile products rules out extensive ash production due to hydromagmatic fragmentation. We apply a recently developed Stereo-Scanning Electron Microscopy (SSEM) technique (Proussevitch et al., 2011) to determine vesicularity features (e.g., bubble size distribution and bubble number density; hereafter BSD and BND, respectively) of ash particles. SSEM analysis provides new insights into magma vesiculation history and fragmentation mechanism leading to major ash-rich eruptions. We conclude that extensive ash production was related to essentially magmatic processes involving high degrees of decompression in shallow magma reservoirs.

Description: Published

Description: 98-107

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Understanding how long-term subduction dynamics relates to the short-term seismicity and crustal tec tonics is a challenging but crucial topic in seismotectonics. We attempt to address this issue by linking long-term geodynamic evolution with short-term seismogenic deformation in the Northern Apennines. This retreating subduction orogen displays tectonic and seismogenic behaviors on various spatiotemporal scales that also characterize other subduction zones in the Mediterranean area. We use visco-elasto-plastic seismo-thermo-mechanical (STM) modeling with a realistic 2D setup based on available geological and geophysical data. The subduction dynamics and seismicity are coupled in the numerical modeling, and driven only by buoyancy forces, i.e., slab pull. Our results suggest that lower crustal rheology and lithospheric mantle temperature modulate the crustal tectonics of the Northern Apennines, as inferred by previous studies. The observed spatial distribution of upper crustal tectonic regimes and surface displacements requires buoyant, highly ductile material in the subduction channel beneath the internal part of the orogen. This allows protrusion of the asthenosphere in the lower crust and lithospheric delamination associated with slab retreat. The resulting surface velocities and principal stress axes generally agree with present-day observations, suggesting that slab delamination and retreat can explain the dynamics of the orogen. Our simulations successfully reproduce the type and overall distribution of seismicity with thrust faulting events in the external part of the orogen and normal faulting in its internal part. Slab temperatures and lithospheric mantle stiffness affect the cumulative seismic moment release and spatial distribution of upper crustal earthquakes. The properties of deep, sub-crustal material are thus shown to influence upper crustal seismicity in an orogen driven by slab retreat, even though the upper crust is largely decoupled from the lithospheric mantle. Our simulations therefore highlight the effect of deep lower crustal rheologies, self-driven subduction dynamics and mantle properties in controlling shallow deformation and seismicity.

Description: Published

Description: 228481

Description: 1T. Struttura della Terra

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: The 10Be/9Be ratio is commonly employed as a tool for establishing the stratigraphic position of paleomagnetic excursions and reversals whenever the traditional paleomagnetic approach fails to provide conclusive results. In particular, it is held that 10Be production rates in the atmosphere depend on the strength of the Earth’s magnetic field, and the fallout and deposition of cosmogenic beryllium at the surface happen on a very short time scale. However, investigations performed on terrestrial and marine successions demonstrate that the 10Be record and the paleomagnetic signal are often asynchronous. Mechanisms that control the conveyance and deposition of cosmogenic 10Be to the seafloor are still ambiguous and poorly documented. Here, we discuss the dynamics of 10Be in a central Mediterranean marginal marine depositional scenario characterized by a pervasive terrigenous influx. Our data show that a very close correlation exists between 10Be concentrations and the local proxy of rainfall rates and regimes (pollen), indicating that a considerable 10Be transport from the mainland may occur in response to the remobilization of terrestrial reservoirs during periods of increased runoff. Superimposed is a dynamic oceanographic setting that further controls the preservation potential of 10Be at the bottom, in terms of changing water chemistry and/or composition of the sedimentary flux to the seafloor. Results of our investigation suggest that, in particular environmental and depositional settings, the interplay between climate, terrigenous yield and oceanography may jeopardize the sedimentary depiction of the meteoric 10Be contribution, thus challenging the use of 10Be for tracking the stratigraphic position of geomagnetic reversals.

Description: Published

Description: 106039

Description: 1A. Geomagnetismo e Paleomagnetismo

Description: JCR Journal

Description: Total CO2 output from fumaroles, bubbling and water dissolved gases and soil gases was investigated at Pantelleria Island volcano, Italy. The preliminary results indicate an overall output of 0.39 Mt a−1 of CO2 from the island. The main contribution to the total output was from diffuse soil degassing (about 0.32 Mt a−1), followed by dissolved CO2 (0.034 Mt a−1), focussed soil degassing (0.028 Mt a−1) and bubbling CO2 (0.013 Mt a−1). The contribution of CO2 from fumarole gases was found to be negligible (1.4×10−6 Mt a−1). Carbon-13 values for CO2 coupled with those for associated He in gases from fumaroles and sites of focussed soil degassing clearly rule out any significant organic CO2 component and suggest a common mantle origin for these gas species. The inferred mantle source beneath Pantelleria would seem to have peculiar geochemical characteristics, quite distinct from those of mantle producing MORB but compatible with those of magmatic sources of central Mediterranean and central European volcanoes. These findings indicate that the Pantelleria volcanic complex is a site of active mantle degassing that is worthy of attention for future geochemical surveillance of the island.

Description: Published

Description: 883-894

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Volcanic activity atMt. Etna in the last decade hasmostly beenmanifested by sequences of short paroxysmal episodes characterised by powerful lava fountains and high eruption columns. On the 23 February 2013, an exceptionally intense episode occurred at the New South-East Crater, producing a fountain N800 m high (among the highest ever recorded at Etna) and a ~9 km eruption column that dispersed ash N400 kmfromthe vent. Textural and petrographic analyses of lapilli revealed that magma erupted during the high-intensity phase is characterised by lowmicrolite contents (b7 area%), high vesicularity (76–83%), and high vesicle number densities (6–8.2 × 106 cm−3). The short-lived initial Strombolian explosions removed viscous magma from the conduit, enabling the rapid ascent of gas-rich, microlite-poor magma and the eruption of an 800 mhigh fountain and 9 kmhigh eruption column. For the 23 February eruption, the high vesicularity and lowmicrolite content of the pyroclasts support the hypothesis that volatile-rich magma was the driver of the high intensity lava fountain. This eruptive event, along with three other recent events at Etna over the last 15 years, can be defined as subplinian based on eruption rate and column height, but also generated incandescent 800–1000 m fountains. For these reasons, we propose to term this event, and others at Etna characterised by similar eruption features and parameters, as subplinian fountaining events.

Description: Published

Description: 241-250

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: The elevation of an orogenic belt is commonly related to crustal/lithosphere thickening. Here, we discuss the Apennines as an example to show that topography at a plate margin may be controlled not only by isostatic adjustment but also by dynamic, mantle-driven processes. Using recent structural constraints for the crust and mantle we find that the expected crustal isostatic component explains only a fraction of the topography of the belt, indicating positive residual topography in the central Apennines and negative residual topography in the northern Apennines and Calabria. The trend of the residual topography matches the mantle flow induced dynamic topography estimated from regional tomography models. We infer that a large fraction of the Apennines topography is related to mantle dynamics, producing relative upwellings in the central Apennines and downwellings in the northern Apennines and Calabria where subduction is still ongoing. Comparison between geodetic and geological data on vertical motions indicates that this dynamic process started in the early Pleistocene and the resulting uplift appears related to the formation and enlargement of a slab window below the central Apennines. The case of the Apennines shows that at convergent margins the elevation of a mountain belt may be significantly different from that predicted solely by crustal isostasy and that a large fraction of the elevation and its rate of change are dynamically controlled by mantle convection.

Description: Published

Description: 163-174

Description: 1T. Struttura della Terra

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: The Mw = 7.3 earthquake near the Iran-Iraq border in west Iran (34.911°N, 45.959°E) occurred at 18:18:17 UTC (LT = UTC + 03:30), November 12, 2017 as the result of oblique-thrust faulting at mid-crustal depth (∼19 km). Median, Kalman filter and Neural Network, as three standard, classical and intelligent methods, have been implemented to investigate three months of GPS Total Electron Content (TEC) measurements and to detect the striking anomalous variations around the time and location of the mentioned earthquake. The first method detects unusual variations, 9 days before the event, between 21:00 and 22:00 UTC. The other two methods of Kalman filter and Neural Network detect another clear anomaly on 11 days preceding the earthquake at 16:00 UTC. These findings are two of the outstanding results of GPS-TEC precursor analysis. This paper also presents the results of Swarm satellites (Alpha, Bravo and Charlie) data analysis inside the Dobrovolsky area around the Iran earthquake epicenter during the period from 1 August to 30 November 2017. The time series and orbital analysis of six measured parameters including electron density, electron temperature, magnetic scalar and vectors (X, Y, Z) components indicate irregular variations between 8 and 11 days prior to the occurrence of the earthquake. Since the variations of the solar and geomagnetic indices follow a normal behaviour during the whole period of the observed ionospheric anomalies between 8 and 11 days before the earthquake, it can be concluded that multi-precursors analysis has an important role to acknowledge the seismo-LAI (Lithospheric-Atmospheric-Ionospheric) anomalies associated to strong earthquakes such as this case. Furthermore, some physical and chemical atmospheric parameters from a climatological database are investigated and some interesting anomalies above two standard deviations prior to the earthquake are found. This paper shows not only anomalies in atmosphere and ionosphere but also a contemporary analysis of different data sources to detect the possible Lithosphere Atmosphere Ionosphere Coupling (LAIC) effects.

Description: ASI

Description: Published

Description: 143-158

Description: 7T. Variazioni delle caratteristiche crostali e precursori sismici

Description: JCR Journal

Description: A multidisciplinary field campaign was carried out at Nisyros Island (Greece). Hydrothermal gases were sampled and analysed, and CH4 and CO2 fluxes from the soils were measured with the accumulation chamber method. The sampling area (Lakki plain) covers an area of about 0.08 km2, and includes the main fumarolic areas of Kaminakia, Stefanos, Ramos, Lofos and Phlegeton. Flux values measured at 130 sites range from −3.4 to 1420 mg m−2 d−1 for CH4 and from 0.1 to 383 g m−2 d−1 for CO2. The fumarolic areas show very different CH4 degassing patterns, Kaminakia showing the highest CH4 output values (about 0.8 t a−1 from an area of about 30,000 m2) and Phlegeton the lowest (about 0.01 t a−1 from an area of about 2500 m2). The total output from the entire geothermal system of Nisyros should not exceed 2 t a−1. Previous indirect estimates of the CH4 output at Nisyros, based on soil CO2 output and CH4/CO2 ratios in fumarolic gases, were more than one order of magnitude higher. The present work further underscores the utmost importance of direct CH4 flux data because indirect methods totally disregard methanotrophic activity within the soil. Ten soil samples were collected for CH4 consumption experiments and for metagenomic analysis. Seven of the soil samples showed small but significant CH4 consumption (up to 39.7 ng g−1 h−1) and were positive for the methanotrophs-specific gene (pmoA) confirming microbial CH4 oxidation in the soil, notwithstanding the harsh environmental conditions (high temperature and H2S concentrations and low pH).

Description: Published

Description: 119546

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: JCR Journal

Description: Quantification of the CO2 released by the volcanoes to the atmosphere is relevant for the evaluation of the balance between deep-derived, biogenic and anthropogenic contributions. The current study estimates the CO2 released from Furnas do Enxofre degassing area (Terceira Island, Azores archipelago) by applying an approach that integrates the flux of CO2 fromthe soilwith the δ13C-CO2 values. A deep-derived CO2 output of 2.54 t d−1 is estimated for an area of ~23,715 m2. High biogenic-derived CO2 flux values (~45 g m−2 d−1) associated with light carbon isotopic content (δ13C=−28‰±1.1‰) are detected and explained by the type of vegetation that characterizes the study site. Carbon isotopic compositions of the CO2 (−6.4‰±1.2‰) measured in olivine-hosted fluid inclusions of the Terceira basalts are presented for the first time and contribute to defining the mantle-CO2 signature. Differences between these values and heavier carbon isotope values from gas in fumaroles at Furnas do Enxofre (−4.66‰to−4.27‰) are explained by the carbon isotopic fractionation occurring when CO2 reacts to form calcite in the geothermal reservoir at temperatures N180 °C. A clear correlation between the soil temperature and deep CO2 fluxes is observed and the integration of the diffuse degassing information with the composition of the fumarolic emissions allows estimating a thermal energy flux of 1.1 MW.

Description: Published

Description: 106968

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: 4V. Processi pre-eruttivi

Description: JCR Journal

Description: Greece is a region characterised by intense geodynamic activity that favours the circulation of hydrothermal fluids in the crust transporting volatiles from either the deep crust or the mantle to the surface. Elevated heat flow values are detectable at Sperchios Basin and North Euboea (central Greece), two areas defined by a system of deeply rooted extensional faults and Quaternary volcanic activity. This setting contributed to the formation of numerous hydrothermal systems, which are mostly expressed as CO2-rich thermal springs with intense bubbling. The CO2 output from six bubbling pools has been determined by flux measurements with the use of the floating chamber method. The highest bubbling CO2 output has been found at Thermopyles and Psoroneria (0.6 and 0.84 t/d, respectively), where the outgoing channels have an elevated flow (〉250 l/s) of gas-charged water (〉15 mmol/l of CO2). Although no bubbling is noticed along the stream, the CO2 content decreases by an order of magnitude after few hundreds of metres, indicating an intense degassing from the water. Taking into account the water flow and the amount of CO2 lost to the atmosphere, the CO2 output of the outgoing channels is quantified in 12.5 t/d for Thermopyles and 9.23 t/d for Psoroneria. Output estimation has also been made for the other springs of the area. The diffuse CO2 release from the outgoing channels has always been higher respect to that of the visible bubbling, suggesting that most of the degassing is “hidden”. Furthermore, the loss of CO2 from the water has determined a shift in dissolved carbonate species as demonstrated by the pH increase along the channel that led eventually to an oversaturation in carbonate minerals and therefore travertine deposition. The total CO2 output to the atmosphere of the study area is estimated at ~27 t/d, with the major contribution deriving from the degassing along the outflow channels of the thermal springs. Such output is comparable to that of the single active volcanic systems along the South Aegean Active Volcanic Arc and highlights the importance of “hidden” degassing along CO2-oversaturated streams.

Description: Published

Description: 104660

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: JCR Journal

Description: The Mediterranean area has been inhabited since long time and the development of human settlements along its coastlines allowed to “record” the occurrence of natural disasters as tsunamis in different coastal settings. Nowadays, the same coastal areas host large cities and critical infrastructures and the availability of historical and geological data on the tsunamis of the past, on their characteristics and effects can significantly contribute to the development of adequate mitigation measures, defense actions and better awareness of people living along the coastlines. The knowledge of past tsunamis is one of the keys to better forecast future events: our territory is a natural laboratory where past natural events can replicate in the future with with similar characteristics. All the coastlines may be considered as the geological and geomorphological archive of past inundations. In the Mediterranean area, valuable historical evidence of past tsunamis and several paleotsunami traces exist, these were recently well organized in homogeneous and coherent geographical databases; these represent the core of this manuscript. This type of information, recently improved and enriched, allows to increase the knowledge of tsunami histories of the Mediterranean sites most prone to tsunamis, providing information on the intensity and frequency of past events.

Description: Published

Description: 6T. Studi di pericolosità sismica e da maremoto

Description: N/A or not JCR

Description: Transient volcanic plumes are time-dependent features generated by unsteady eruptive sources, having similar eruption duration and plume development timescales. Their morphological evolution reflects both the discharge history at the vent and air entrainment, crucial parameters controlling volcanic ash dispersal and impact on the environment and human activities. However, despite its importance, transient plume morphology has been scarcely quantified, due to both observational and analytical hindrances. In this study, we introduce new tools to quantify the initial morphological evolution of transient volcanic plumes by applying fractal analysis and plume's perimeter measurements to thermal high-speed and visible-light high-resolution videos of eruptions. Eruptive plumes from Sakurajima (Japan), Stromboli (Italy), and Fuego (Guatemala) volcanoes were recorded during several field campaigns in 2012–2016. The eruption dataset has been complemented by the fractal analysis of three 2D numerical gas-jet simulations at different Reynolds number (2 × 103, 5 × 103 and 10 × 103) in order to provide reference configurations to compare with the natural cases. The two shape analysis methods used show different sensitivities. The ratio between plume and bounding box perimeters appears to be more perceptive of punctual dynamical variations, while fractal analysis reflects the overall plume evolution. Both methods highlight that plume shape complexity increases over time and is related to the formation and development of smaller scale vortexes. The variability of the rate of fractal dimension increase over time (αD) effectively captures plume evolution. It also appears that αD correlates with the ash eruption rate (AER) evolution and the instability of the source. This study shows that discharge history and intensity at the vent are the first order control on plume's shape evolution and, by inference, on its air entrainment ability.

Description: Published

Description: 59–71

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Fluid primary source(s) and chemical-physical processes controlling water and gas chemistry of thermal springs from Eastern Cordillera, sub-Andean Ranges and Santa Bárbara (Jujuy Province, northern Argentina) were investigated to provide information for a preliminary evaluation of the geothermal potential in these areas. Thermal manifestations in Eastern Cordillera (Reyes) and part of those in the western sector of sub-Andean Range (Aguas Calientes) are fed by shallow aquifers, interacting with Quaternary- Neogene rocks and the upper portion of Pliocene-Miocene formations (Orán Group), whereas the meteoric water recharge area is located at〉2500 m a.s.l., corresponding to Chañi hill. Differently, El Jordán thermal spring in the sub-Andean Range is fed by a hydrothermal aquifer hosted within highly porous and fractured formations of the Salta Group (Yacoraite Formation) and recharged by meteoric water from Sierra de Calilegua (∼1500m a.s.l.). The latter is the recharge area of the La Quinta geothermal waters as well, but these have been fed at higher altitudes (〉 2500 m a.s.l.) in the range. The hydrothermal reservoir feeding the other thermal springs from the Santa Barbara system (Caimancito, El Palmar, and Siete Aguas) is recharged by meteoric water from Zapla Ranges and Santa Barbara Hill at〈2500m a.s.l. The high-TDS (〉 16,000 mg/L) Na+-Cl- La Quinta thermal springs are produced by interaction with the evaporite deposits of Salta Group, including halite, whereas the chemistry of El Palmar, El Jordán and Caimancito thermal springs, showing a Na+-SO4 2-(Cl−) composition, depends on mixing with shallower SO4 2--rich waters interacting with gypsum deposits of Anta Formation. Dissolved and bubbling gases from all the investigated provinces are related to CO2- and CH4-rich crustal fluids produced by both thermogenic processes occurring within the hydrothermal systems and microbial activity at relatively low depth, with low to negligible mantle contribution, as indicated by the 3He/4He values ≤ 0.21 Ra. The fluid reservoir feeding the Quinta thermal springs shows the highest estimated temperatures (〉 200 °C), which, considering the depth of Salta Group in the Santa Barbara system (~2000 m), support the idea, suggested by previous authors, of an anomalous geothermal gradient for this area, a promising pre-requisite for future exploitation of the geothermal resource.

Description: Published

Description: 102627

Description: 1TR. Georisorse

Description: JCR Journal

Description: As far as the European continent, Region Campania in Southern Italy presents an almost unique combination - in terms of both variety and intensity-of potential risks for the residents: this densely populated area is actually most notably exposed to hydrogeological (flood and landslides), seismic, volcanic hazards In such a setting, alongside with an up-to-date scientific approach to risks analysis and the constant update of emergency plans, it is of paramount importance that a “risk awareness culture” should be developed by the residents. In order to maximize the effectiveness of the communication campaigns to support and improve such a culture, a study of risk perception has been carried out in 12 municipalities and 2 territorial unions of Campania Region. Different areas have been examined, the overall exposure of each almost always being characterised by a prevalent specific risk: seismic, volcanic, hydrogeological. The results of this surveys show that the historical memory has a crucial role on the hazards perception. It's also worth of noting that few communities consider that they have been sufficiently well-informed by civil protection agencies and/or authorities about the natural hazards specific to their area and the practical procedures for evacuation. To overcome these deficiencies emergency plans should be designed, developed and practised through the collaboration of all key stakeholders, from civil protection authorities to the residents communities.

Description: Published

Description: id 101164

Description: 6SR VULCANI – Servizi e ricerca per la società

Description: JCR Journal

Description: On 26th January 2001, an earthquake of magnitude Mw 7.7 occurred near Bhuj, in northwestern India, resulting in severe environmental effects. No unequivocal primary surface rupture was observed for the earthquake, but it caused widespread liquefaction and lateral spreading in the Rann of Kachchh and Little Rann. After the earthquake, several researchers collected field evidence of secondary surface rupture, rockfall, dry craters, and surface manifestations of liquefaction, including the formation of mud volcanoes and lateral spreads, in the meizoseismal area. Analysis of pre- and post-earthquake satellite images suggests that several “dry” streams in the Rann of Kachchh began to flow due to extensive liquefaction induced by the earthquake. In this present study, the macroseismic intensity of the Bhuj earthquake is evaluated by considering these environmental effects and applying the ESI-07 intensity scale to the affected area. As an outcome, the epicentral intensity of the 2001 Bhuj earthquake was determined to be XI. According to historical records and seismic catalogs, 16th June 1819 Allah Bund earthquake caused prominent surface rupture which was not so clear in the case of 2001 Bhuj earthquake, but the secondary effects were similar for both earthquakes. Considering the environmental effects caused by the 1819 Allah Bund earthquake, an intensity of XI was estimated for the epicentral area. For both earthquakes, the ESI scale yields a significant difference of one to two degrees with the traditional intensity scales. The 2001 Bhuj earthquake and 1819 Allah Bund earthquake shows similar ESI-07 intensity of XI despite of different epicentral locations. This implies the reliability of ESI-07 scale application for different earthquakes of similar dimensions in the same geological setting. This study contributes to the application of ESI-07 scale for Indian earthquakes, especially reverse faulting events, and to the future improvement of the ESI scale with emphasis on its applicability to historical earthquakes on the Indian subcontinent. Also, this study may help in future land use planning in the meizoseismal area of 1919 Allah Bund and 2001 Bhuj earthquakes

Description: Published

Description: 127-143

Description: 1T. Struttura della Terra

Description: 2T. Deformazione crostale attiva

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal

Description: The diffuse emission of CO2 from the south east sector of Nisyros caldera (Lakki plain) has beenmeasured during a detailed survey (~1400 soil CO2 flux measurements) performed in October 2018. The gas emissions are fed by hydrothermal sources and, inminor part, by the soil biogenic activity whosemean CO2 flux (4 gm−2 d−1) is here estimated for the first time. The total amount of hydrothermal CO2 reaches 92 ± 8 t/d, a value that is slightly higher than that estimated with the same method between 1999 and 2001 (74 ± 7 t/d). The gas is emitted by different diffuse degassing structures (DDSs), including volcanic-hydrothermal structures (craters and domes) and NE-SWand NW-SE-trending tectonic lineaments. Even if the total CO2 emission is not particularly high at Nisyros (close to themedian of CO2 emissionsmeasured in volcanoesworldwide), the process is very energetic. The thermal energy associated with the shallow condensation of the steam in the DDSs reaches ~60MW, whilewe estimate at 134–270MWthe total amount of thermal energy involved in the convective rising of the deep geothermal liquids that transport the gas from the depth toward the surface. This large flux of energy could dramatically increase during future earthquakes by addition of heat and mass from a deep hydrothermal reservoir, potentially triggering hydrothermal explosions, as it happened several times in the past few centuries.

Description: Published

Description: 44-53

Description: 1TR. Georisorse

Description: JCR Journal

Description: The shear-sensitive microalga Heterosigma akashiwo is known to produce brevetoxin-like compounds that are active in voltage-dependent sodium channels. In this work, we present a study on the production of anaesthetic extracts from H. akashiwo biomass obtained in low-shear bioreactors at different growth phases. The photobioreactors (PBRs) used had specific configurations and were operated in such a way as to avoid cellular damage by hydrodynamic stress. Cultures were developed in small static-control flasks and PBRs with volumes ranging from 1.5 L to 200 L. The bioactivity of the produced extracts was assessed in vitro (Neuro-2a cell-based assay) and in vivo (Zebra fish model). Bioactivity depended slightly on the growth phase and culture system, with greater toxicity with the Neuro-2a model when stationary-phase extracts were used. Interestingly, extracts were not cytotoxic against other human cell lines. Steady production of anaesthetic bioactives was observed. In vivo anaesthetic efficacy, assessed with the Zebra fish model, was similar to that of commercial products, and without any observed mortality at 24-h post exposure.

Description: Plankton composition and density, and domoic acid (DA) content in microplankton and mesozooplankton were assessed over the northern Patagonian coastal shelf in late austral summer 2013. Maximum values of DA in these two plankton fractions as well as maximum densities of both Pseudo-nitzschia spp. (mainly the toxigenic P. australis) and DA potential vectors were only detected on the southern coast of San Matías Gulf and the eastern coast of Valdés Peninsula. In this zone, waters were characterized by low temperature, high nitrate, and intermediate values of silicic acid and phosphate. Based on the high association between the DA values recorded and the values of either micro- and mesozooplankton grazer density or biomass, we inferred that DA transfer from Pseudo-nitzschia spp. occurred largely through the small copepods Euterpina acutifrons and Oithona nana, Calanidae nauplii and Calanidae copepodites, Noctiluca scintillans, and euphausiid developmental stages. Small copepods, Calanidae nauplii and copepodites, and cladocerans were proposed as novel DA vectors although this suggestion requires experimental confirmation. This study provides the first lines of evidence of the co-occurrence of Pseudo-nitzschia spp. blooms with DA production and accumulation in mesozooplanktonic grazers at the base of the food web and of the environmental and oceanographic conditions that seem to favor these processes over the northern Patagonian shelf coasts.

Description: The LOHAFEX iron fertilization experiment consisted in the fertilization of the closed core of a cyclonic eddy located south of the Antarctic Polar Front in the Atlantic sector of the Southern Ocean. This eddy was characterized by high nitrate and low silicate concentrations. Despite a 2.5 fold increase of the chlorophyll-a (Chl-a) concentrations, the composition of the biological community did not change. Phytoplankton biomass was mostly formed by small autotrophic flagellates whereas zooplankton biomass was mostly comprised by the large copepod Calanus simillimus. Efficient recycling of copepod fecal pellets (the main component of the downward flux of organic matter) in the upper 100–150 m of the water column prevented any significant deep export of particulate organic carbon (POC). Before fertilization, dissolved iron (DFe) concentrations in the upper 200 m were low, but not depleted, at ~0.2 nM. High DFe concentrations appeared scattered from day 14 onwards as a result of the grazing activity. A second fertilization on day 21 had no significant effect on the DFe and Chl-a standing stocks. Work with unfiltered samples using different acidification protocols revealed that, by midway of LOHAFEX, rapid recycling of iron-replenished copepod fecal pellets explained the source of bioavailable iron that prolonged the duration of the bloom for many weeks. Here we present the evolution of the organic speciation of iron in the upper 200 m of the water column during LOHAFEX by a Competing Ligand Equilibrium method using voltammetry. During the first 12 days of the experiment, ligands of an affinity for iron similar to the ligands found before fertilization (logK′Fe′L~11.9) accumulated in fertilized waters mostly in the upper 80 m (from ~1 nM to ~2.5 nM). The restriction of ligand accumulation to the depth of Chl-a penetration points to exudation by the growing autotrophic population as the initial source of ligands. From day 5 onwards, we found in many samples a new class of ligands (L1) characterized by a significant higher conditional stability constant than the background complexation (logK′Fe′L1~12.9). During the middle section of the experiment (days 12 to 25) the accumulation of overall ligands and specifically L1, reached an upper limit in surface waters (at ~3 nM). Overall ligands and L1 accumulation was also observed below the mixed layer depth indicating that grazing was the process behind ligand release. During the last 10 days of the experiment ligands kept accumulating in deep waters but suffered a small decrease in the upper 50 m of the water column caused by the vanishing of L1. Ligand removal restricted to the euphotic layer was probably caused by photodegradation. A high correlation between [DFe] and [L1] suggested that recycled iron (released during grazing and copepod fecal pellet cycling) was in the form of FeL1 complexes. We hypothesize that the iron binding ligands released to the dissolved phase during LOHAFEX were mostly photosensitive intracellular ligands rapidly degraded in extracellular conditions (e.g.: pigments). Sloppy feeding by copepods and recycling of cells and cellular material in copepod fecal pellets caused the transfer of particulate ligands to the dissolved phase as zooplankton built up as a response to the blooming community.

Description: The late Pleistocene trachytic Campanian Ignimbrite (〉 300 km3 DRE, ca. 39 ka) covers the Campanian Plain (Italy) around Naples. It is found behind ridges〉1000m high at 80 km from the source in the Campi Flegrei caldera. This points towards very dilute currents, that together with the huge amount of discharged magmatic material, suggest a magma reservoir highly enriched in volatiles. The huge volume of magma that extruded during the Campanian Ignimbrite eruption differentiated and mixed at shallow depth (6–3 km), as shown by modelling of the petrologic and geochemical features of the erupted products together with melt inclusion-based studies of gas-melt saturation. With respect to compositionally similar but lower magnitude Phlegraean eruptions (e.g., Agnano-Monte Spina,〉1 km3 DRE, ca. 4.6 ka), the large amount of volatiles discharged by Campanian Ignimbrite was likely due to fractional crystallization of the lowermost portion of its magmatic reservoir. Because of the long residence time of the Campanian Ignimbrite magmatic system within the crust, an efficient decoupling took place during the upward migration of volatile elements in response to a chromatographic fractionation between H2O and CO2. This caused early pulses of nearly pure CO2 (CO2-fluxing), followed by a long-lasting H2O enrichment which yielded dissolved H2O contents up to 6–7 wt%. An overpressurized CO2- dominated gas cap was consequently produced, uniformly distributed at the top of the magma chamber. The onset of the eruption tapped this cap and generated Plinian columns, causing depressurization and fast volume decrease that facilitated, or even drove, the caldera collapse. H2O-rich magma was discharged during the following phase, characterised by pyroclastic density currents. The uniform distribution of the high values of void fraction (〉 70%) and the high degree of vesicle connectivity throughout the magma body testify to the huge abundance of volatiles. These percolate from the crystallizing basal layers and determine the volatile-melt fining process yielding an efficient separation between H2O and CO2. The gas saturation-based estimates of the tapped foamy magma are compatible with the extent of magma chamber roof collapse, the strong expansion revealed by textural data, and the transport and deposition mechanisms, reflecting depressurization and inflation of the volatile-rich magma within the collapsed and laterally confined caldera.

Description: Published

Description: 1-14

Description: 4V. Processi pre-eruttivi

Description: JCR Journal

Description: Detecting changes of sediment boundaries on the seafloor is important for a better understanding of sediment dynamics and related impacts to benthic habitats. Side-scan sonars (SSS) perform more cost-effectively in shallow waters than other acoustic systems because of their larger swath widths, and the resolution of its images does not change with varying water depth. However, as they are generally towed behind the survey vessel, they tend to have lower positioning accuracy, which makes them unreliable for change detection analyses. In this study, we present a workflow that processes SSS data in a way that makes them fit for change detection analyses. To test the capacity of SSS mosaics for change detection, we used a free software called “Digital Shoreline Analysis System”, which was developed by the United States Geological Survey for ArcGIS version 10.4 onwards. The methods were applied in three areas in the Sylt Outer Reef, German Bight, North Sea. Our results showed that with appropriate processing, SSS mosaics could be used for change detection of sharp sediment boundaries. We found a common trend in the sediment distribution patterns of coarse sediments by monitoring the movement of their boundaries. The boundaries moved in northeast-southwest direction and boundary movements of less than 20 m were typically observed. The methods presented here are semi-automated, repeatable, and replicable, which has potential for wide-scale monitoring of sediment distribution patterns.

Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 33(4), (2020): 1535-1545, doi:10.1175/JCLI-D-19-0547.1.

Description: In a transient warming scenario, the North Atlantic is influenced by a complex pattern of surface buoyancy flux changes that ultimately weaken the Atlantic meridional overturning circulation (AMOC). Here we study the AMOC response in the CMIP5 experiment, using the near-geostrophic balance of the AMOC on interannual time scales to identify the role of temperature and salinity changes in altering the circulation. The thermal wind relationship is used to quantify changes in the zonal density gradients that control the strength of the flow. At 40°N, where the overturning cell is at its strongest, weakening of the AMOC is largely driven by warming between 1000- and 2000-m depth along the western margin. Despite significant subpolar surface freshening, salinity changes are small in the deep branch of the circulation. This is likely due to the influence of anomalously salty water in the subpolar intermediate layers, which is carried northward from the subtropics in the upper limb of the AMOC. In the upper 1000 m at 40°N, salty anomalies due to increased evaporation largely cancel the buoyancy increase due to warming. Therefore, in CMIP5, temperature dynamics are responsible for AMOC weakening, while freshwater forcing instead acts to strengthen the circulation in the net. These results indicate that past modeling studies of AMOC weakening, which rely on freshwater hosing in the subpolar gyre, may not be directly applicable to a more complex warming scenario.

Description: We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Table 1 of this paper) for producing and making available their model output. We also thank John Marshall for helpful discussions on the driving mechanisms of the AMOC, and three anonymous reviewers whose comments greatly improved the manuscript. This work was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program Award 80NSSC17K0372, and by National Science Foundation Award OCE-1433132.

Description: 2020-07-20