ALBERT

Description: Tor Caldara natural reserve hosts the southernmost discharge of endogenous gas of Colli Albani volcano (mostly CO2 with a relevant H2S content up to 6.3 vol.%). Gas discharges in zones where past sulfur mining removed the impervious surficial cover (e.g. Miniera Grande and Miniera Piccola) and along tectonic fissures. A structural study of the reserve has shown the presence of two zones with different characteristics: prevailing directions NS and N30° in the northern zone; EW and N60° in the southern one. In MarchJuly 2012 a geochemical study was carried out, including a soil CO2 flux survey and continuous monitoring (from 2 to 11 days) of air concentration of CO2 and H2S in 12 sites of the reserve. Environmental parameters were also monitored. Total diffuse soil flux of endogenous CO2 was estimated to 17.48 ton*day1 from 1,259 measurements over a 0.47 km2 surface, with 6.56 ton*day1 only from Miniera Grande. This is the second highest value of soil CO2 flux at Miniera Grande, after that of 2005 (9.25 ton*day1) and is significantly higher than in 2009 (1.20 ton*day1). As both the 2005 and 2012 surveys were made shortly after earthquakes with epicentres near to Tor Caldara (max ML= 4.7 in 2005 and 3.5 in 2012), data confirm that soil CO2 flux increases during earthquakes because of seismic rock microfracturing and soil shaking. Hazardous air concentrations have been found only for H2S, up to immediately lethal values (5651,124 ppm) and with potentially lethal values (≥ 250 ppm) long persisting (up to 12h27’) in several no wind nights. Instead, the CO2 air concentration remained always well below dangerous levels (maximum recorded value = 2.1 vol.%). The most hazardous gas releasing sites were found in Miniera Grande and in a small pond NE of Miniera Piccola, where the carcasses of mammals and other small animals are frequently found. The killer gas is H2S, and the dangerous sites should be appropriately fenced to prevent access to people and animals.

Description: Regione Lazio Civil Protection Department

Description: Published

Description: 1-48

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

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: 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: 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: Slope dynamics in volcanic environments comprise a wide spectrum of phenomena, from large lateral collapse to shallow debris remobilization, which may represent a major threat for human communities and infrastructures. Many volcanos built up from the ocean floor and large portions of the volcano edifice are submerged. In these settings, only the edifice’s summit can be investigated by terrestrial remote sensing and in-situ approaches. Growth and destruction, including tectonics and gravitational phenomena, affect entire volcano flanks and are not limited to the physical boundary of the sea level but could comprise their subaqueous parts.

Description: Published

Description: 2615–2618

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

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