ALBERT

Description: Radon monitoring represents an important investigation tool for environmental changes assessment and geochemical hazard surveillance. Despite anomalous radon emissions are commonly observed prior to earthquakes or volcanic eruptions, radon monitoring alone is not yet successful in correctly predicting these catastrophic events because contrasting radon signals are unexpectedly measured by lithologically distinct areas. This contribution aims to summarize and integrate natural and laboratory studies pertaining to the transport behavior of radon in different rock types experiencing variable stress and thermal regimes at subvolcanic conditions. The final purpose is to ignite novel and pioneer experimental researches exploring the causes and consequences of radon anomalous emissions, in order to elucidate in full the relationship between the physicochemical changes in substrate rocks and the radon signal.

Description: Published

Description: 309-328

Description: 4V. Processi pre-eruttivi

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: Multiparametric observations integrate signals from different techniques into a unified time and space frame, and are key in understanding and monitoring the evolution of volcanic systems and eruptive activity. Mafic explosive eruptions, with a relatively high frequency of occurrence and low intensity, allow for detailed multiparametric observations at a relatively close distance. Typically, pyroclast ejection in these eruptions is not steady, but is characterized by the occurrence of ejection pulses, linked to pressure release events and featuring a characteristic nonlinear decay of pyroclasts exit velocity. Pulse frequency, duration, and exit velocity define the dominant eruptive style, function of the volume and pressure of the released gas, conduit size, and magma rheological-mechanical properties. No important differences in pressure and velocity divide eruptions with different magnitude and style. Ejection pulses influence the geophysical signature, plume development, and the emplacement of ballistic volcanic projectiles at eruptions from Strombolian to Vulcanian styles.

Description: Published

Description: 379-411

Description: 4V. Processi pre-eruttivi

Description: 5V. Processi eruttivi e post-eruttivi

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

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: Major, minor and rare earth elements were analyzed in the acid sulphate - chloride thermal springs associated to Puracé volcano – hydrothermal system. The waters of Puracé were classified in 2 different groups as a function of the physico-chemical parameters and element distributions. Group 1 is characterized by the highest pH (⁓ 3.5), an outlet temperature of ⁓ 81 °C and a strong depletion of Fe, Al, Si and Ba with respect to the isochemical dissolution of the average volcanic local rock. Group 2 waters have lower pH values ⁓ 1.9 and temperature (⁓ 48 °C) compared with Group 1. Moreover, Group 2 is not characterized by a typical pathway representing the congruent dissolution of the rock and shows a distribution of major and minor elements that is more close to the near-congruent dissolution of the average volcanic local rock with respect to Group 1. These geochemical features of major and minor elements allow to propose that the chemical composition of the waters of Group 1 is strongly affected by the precipitation of secondary minerals such as alunite, jarosite, kaolinite, barite and polymorphs of SiO2. The grouping of waters is also supported by the distribution of dissolved REE normalized to the average volcanic local rock. Group 1 shows REE patterns strongly depleted in light rare earth elements (LREE), typical of water that formed alunitic and/or kaolinitic rocks. On the contrary, Group 2 is characterized by flat patterns, in according to the near-congruent dissolution of the rocks. REE dissolved in waters of Puracé were compared with REE in the acidic waters of Nevado del Ruiz and Azufral Colombian volcanoes and with REE in minerals recognized in advanced argillic alteration (alunite, gypsum and kaolinite). Precipitation of secondary minerals is proposed as a common process depleting LREE in acidic sulphate – chlorine waters in volcano – hydrothermal systems. Furthermore, the chemical fractionation of the major and minor elements was interpreted together with the corresponding distributions of REE in order to trace the water – rock interaction processes. Saturation indexes of most common secondary minerals identified in advanced argillic alterations were calculated using PHREEQC software in a range of temperature from 25 to 250 °C. This geochemical approach allows to identify the possible mineral precipitation or dissolution of secondary minerals as well as the temperature at which the water reached equilibrium with a given set of minerals. In Group 1, the precipitation of secondary minerals LREE enriched (alunite minerals and kaolinite) was traced at temperature of precipitation higher than ⁓ 101 °C.

Description: Published

Description: 107106

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

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: Hydrothermally-altered rocks collected at Solfatara volcano, Campi Flegrei caldera complex, Italy, are comparable to zones of steam-heated alterations found at low sulfidation epithermal deposits, and volcanic gases collected at Solfatara have temperatures and C-O-H isotopic compositions akin to those forming low sulfidation epithermal deposits. By contrast, hydrothermal alterations collected at La Fossa volcano, Vulcano island, Italy, are comparable to zones of residual vuggy silica formed in high sulfidation epithermal deposits, and volcanic gases collected at La Fossa have temperatures and C-O-H isotopic compositions comparable to those forming high sulfidation epithermal deposits. At Solfatara, amorphous and hydrous opal-A is responsible for shifts in δ7Li values, from +2.2‰ in fresher rocks, to −3.6‰ in most altered rocks, with increases in Au and Cu concentrations (up to 3 ppb and 96 ppm). The increase in Au and Cu concentrations in progressively-altered rocks resulted from the transport of Cu-Au in magmatic-hydrothermal fluids and their partitioning into pyrite, Fe oxides, phyllosilicates, sulfates, and/or opal-A. It is proposed that the combination of opal-A, decreases in δ7Li values, and increases in Cu and Au concentrations represent an exploration vector for low sulfidation epithermal veins. At La Fossa, α-cristobalite is responsible for shifts in δ7Li values, ranging from −0.9‰ in least-altered rocks, to +4.7‰ in most altered rocks, with decreases in Au-Cu concentrations. The decrease in Au and Cu concentrations in progressively-altered rocks may have resulted from the metasomatism of pyrite and Fe oxides, the dissolution of clinopyroxene and opal, and the invasion of the samples by α-cristobalite. The combination of α-cristobalite, increases in δ7Li values, and decreases in Cu and Au concentrations are proposed as proxies for potential high sulfidation epithermal disseminations. Alternating phases of high eruptive activity and quiescent degassing at volcanoes generally, and at Solfatara and La Fossa specifically, suggest that the physicochemical conditions of individual subvolcanic hydrothermal systems should also be alternating, between conditions that are characteristic of low- and high sulfidation epithermal ore-forming environments, and that the related zones of silicification should be alternating between low δ7Li and high Cu-Au values dominated by opal-A, and higher δ7Li and lower Cu-Au values dominated by α-cristobalite.

Description: Published

Description: 103934

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

Description: JCR Journal