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  • 1
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    Crystallization Kinetics of Alkali Feldspar in Peralkaline Rhyolitic Melts: Implications for Pantelleria Volcano (2021)
    Frontiers
    Details
    Publikationsdatum: 2021-01-25
    Beschreibung: Peralkaline rhyolites, associated with extensional tectonic settings, are medium to low viscosity magmas that often produce eruptive styles ranging from effusive to highly explosive eruptions. The role of pre-eruptive conditions and crystallization kinetics in influencing the eruptive style of peralkaline rhyolitic magmas has been investigated and debated considering equilibrium conditions. However, experimental constraints on the effect of disequilibrium in crystallization in such magmas are currently lacking in the literature. Therefore, we performed isobaric cooling experiments to investigate alkali feldspar crystallization kinetics in peralkaline rhyolitic melts. Experiments were performed under water-saturated, water-undersaturated, and anhydrous conditions between 25 and 100 MPa, at 670–790◦C and with experimental durations ranging from 0.5 to 420 h. Here we present the first data on crystallization kinetics of alkali feldspar, which is the main crystal phase in peralkaline rhyolitic melts, in order to improve our understanding of the evolutionary timescales of these melts and their ability to shift between effusive and explosive activity. Our experimental results indicate that the alkali feldspar nucleation delay can range from hours to several days as a function of undercooling and H2O content in the melt. Thus, a peralkaline rhyolitic magma can be stored at the pre-eruptive conditions for days without important variations of its crystal fraction. This suggests that crystallization may not necessarily play the main role in triggering fragmentation during explosive eruptions of peralkaline rhyolitic magmas.
    Beschreibung: PRIN 2009 (2009PZ47NA_002), FAR2012, PRIN 2017 (2017J277S9 – all MC) and the EU LIFE
    Beschreibung: Published
    Beschreibung: 177
    Beschreibung: 4V. Processi pre-eruttivi
    Beschreibung: JCR Journal
    Schlagwort(e): alkali feldspar ; peralkaline rhyolite ; nucleation delay ; crystallization kinetics ; Pantelleria volcanic system ; Crystallization Kinetics of Alkali Feldspar ; Peralkaline Rhyolitic Melts
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 2
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    Explosivity of basaltic lava fountains is controlled by magma rheology, ascent rate and outgassing (2020)
    Elsevier
    Details
    Publikationsdatum: 2021-03-30
    Beschreibung: 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.
    Beschreibung: RCUK NERC DisEqm project
    Beschreibung: Published
    Beschreibung: 116658
    Beschreibung: 5V. Processi eruttivi e post-eruttivi
    Beschreibung: JCR Journal
    Schlagwort(e): 04.08. Volcanology
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 3
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    Increasing CO2 flux at Pisciarelli, Campi Flegrei, Italy (2018)
    Details
    Publikationsdatum: 2018-03-07
    Beschreibung: The Campi Flegrei caldera is located in the metropolitan area of Naples (Italy) and has been undergoing different stages of unrest since 1950, evidenced by episodes of significant ground uplift followed by minor subsidence, increasing and fluctuating emission strengths of water vapor and CO2 from fumaroles, and periodic seismic crises. We deployed a scanning laser remote-sensing spectrometer (LARSS) that measured path-integrated CO2 concentrations in the Pisciarelli area in May 2017. The resulting mean CO2 flux is 578 246 t d􀀀1. Our data suggest a significant increase in CO2 flux at this site since 2015. Together with recent geophysical observations, this suggests a greater contribution of the magmatic source to the degassing and/or an increase in permeability at shallow levels. Thanks to the integrated path soundings, LARSS may help to give representative measurements from large regions containing different CO2 sources, including fumaroles, low-temperature vents, and degassing soils, helping to constrain the contribution of deep gases and their migration mechanisms towards the surface.
    Beschreibung: Published
    Beschreibung: 1017–1024
    Beschreibung: 4V. Dinamica dei processi pre-eruttivi
    Beschreibung: JCR Journal
    Schlagwort(e): CO2 flux at Pisciarelli, Campi Flegrei, Italy
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 4
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    Plagioclase nucleation and growth kinetics in a hydrous basaltic melt by decompression experiments (2018)
    Details
    Publikationsdatum: 2018-03-23
    Beschreibung: Isothermal single-step decompression experiments (at temperature of 1075 °C and pressure between 5 and 50 MPa) were used to study the crystallization kinetics of plagioclase in hydrous high-K basaltic melts as afunction of pressure, effective undercooling (ΔTeff) and time. Single-step decompression causes water exsolution and a consequent increase in the plagioclase liquidus, thus imposing an effective undercooling (∆Teff), accompanied by increased melt viscosity. Here, we show that the decompression process acts directly on viscosity and thermodynamic energy barriers (such as interfacial-free energy), controlling the nucleation process and favoring the formation of homogeneous nuclei also at high pressure (low effective undercoolings). In fact, this study shows that similar crystal number densities (Na) can be obtained both at low and high pressure (between 5 and 50 MPa), whereas crystal growth processes are favored at low pressures (5–10 MPa). The main evidence of this study is that the crystallization of plagioclase in decompressed high-K basalts is more rapid than that in rhyolitic melts on similar timescales. The onset of the crystallization process during experiments was characterized by an initial nucleation event within the first hour of the experiment, which produced the largest amount of plagioclase. This nucleation event, at short experimental duration, can produce a dramatic change in crystal number density (Na) and crystal fraction (φ), triggering a significant textural evolution in only 1 h. In natural systems, this may affect the magma rheology and eruptive dynamics on very short time scales.
    Beschreibung: MIUR, PRIN 2009, FAR2012 funds to M.R. Carroll.
    Beschreibung: Published
    Beschreibung: 55
    Beschreibung: 4V. Dinamica dei processi pre-eruttivi
    Beschreibung: JCR Journal
    Schlagwort(e): Plagioclase ; Nucleation rate ; Growth rate ; Basaltic melts ; Decompression ; 04.08. Volcanology
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 5
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    The unexpected explosive sub-Plinian eruption of Calbuco volcano (22–23 April 2015; southern Chile): Triggering mechanism implications (2020)
    Details
    Publikationsdatum: 2020-02-24
    Beschreibung: Plinian-type eruptions are extremely hazardous, producing pyroclastic fallout and flows extending many kilometres from the vent. The most commonly invoked eruption trigger for Plinian-type eruptions is the intrusion of fresh magma, generally associated with precursory ground deformation and seismicity days/weeks before eruption. Closed-system internal triggering has also been proposed, such as protracted crystallisation of magma, which can produce a build-up of exsolved volatiles and thus pressurise the system prior to eruption. On 22–23 April 2015 Calbuco volcano, Chile, produced a sub-Plinian eruption with 〈3 h seismic precursory activity and no clear deformation signals in the preceding months. Here, we show that petrological and geochemical evidence do not support a hypothesis of eruption triggering due to pre-eruptive intrusion of fresh magma, but instead are consistent with an internal trigger. We found that basaltic andesitic magma was stored at depths between 8 and 12 km (i.e. 230–320 MPa) beneath Calbuco volcano before the 2015 eruption. The stored magma had an initial temperature of 900–950 °C, was water-saturated (5.5–6.5 wt% H2O) and formed phenocrysts of titanomagnetite, orthopyroxene, clinopyroxene and plagioclase cores (An78–93). Gradual cooling of the magma chamber produced thermal gradients and magma convection, evidenced by plagioclase overgrowth rims (An58–77) and blocky microlites (25–250 μm). Our interpretation is that this continuing crystallisation induced second boiling and an over-pressurisation of the system, leading to the rapid onset of the 2015 eruption. Petrological and geochemical evidence therefore shows that a closed-system magma chamber can evolve into a highly explosive eruption with very little precursory warning, posing a challenge for current volcano monitoring paradigms. We propose that internal triggering should be carefully considered as a mechanism for unexpected sub-Plinian eruptions, prompting a potential revision of existing hazard management strategies.
    Beschreibung: Published
    Beschreibung: 35-50
    Beschreibung: 4V. Processi pre-eruttivi
    Beschreibung: JCR Journal
    Schlagwort(e): Calbuco ; Sub-Plinian eruption ; Internal trigger ; Crystallisation ; Volcanic hazard ; 04.08. Volcanology ; Petrology ; 04.06. Seismology
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 6
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    From magma ascent to ash generation: investigating volcanic conduit processes by integrating experiments, numerical modeling, and observations (2018)
    Details
    Publikationsdatum: 2021-09-03
    Beschreibung: Processes occurring in volcanic conduits, the pathways through which magma travels from its storage region to the surface, have a fundamental control on the nature of eruptions and associated phenomena. It has been well established that magma flows, crystallizes, degasses, and fragments in conduits, that fluids migrate in and out of conduits, and that seismic and acoustic waves are generated and travel within conduits. A better understanding of volcanic conduits and related processes is of paramount importance for improving eruption forecasting, volcanic hazard assessment and risk mitigation. However, despite escalating advances in the characterization of individual conduit processes, our understanding of their mutual interactions and the consequent control on volcanic activity is still limited. With the purpose of addressing this topic, a multidisciplinary workshop led by a group of international scientists was hosted from 25 to 27 October 2014 by the Pisa branch of the Istituto Nazionale di Geofisica e Vulcanologia under the sponsorship of the MeMoVolc Research Networking Programme of the European Science Foundation. The workshop brought together the experimental, theoretical, and observational communities devoted to volcanological research. After 3 days of oral and poster presentations, breakout sessions, and plenary discussions, the participants identified three main outstanding issues common to experimental, analytical, numerical, and observational volcanology: unsteadiness (or transience), disequilibrium, and uncertainty. A key outcome of the workshop was to identify the specific knowledge areas in which exchange of information among the subdisciplines would lead to efficient progress in addressing these three main outstanding issues. It was clear that multidisciplinary collaboration of this sort is essential for progressing the state of the art in understanding of conduit magma dynamics and eruption behavior. This holistic approach has the ultimate aim to deliver fundamental improvements in understanding the underlying processes generating and controlling volcanic activity.
    Beschreibung: Published
    Beschreibung: S0666
    Beschreibung: 4V. Dinamica dei processi pre-eruttivi
    Beschreibung: JCR Journal
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 7
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    A novel protocol for resolving feldspar crystals in synchrotron X-ray microtomographic images of crystallized natural magmas and synthetic analogs (2019)
    Mineralogical Society of America
    Details
    Publikationsdatum: 2021-09-03
    Beschreibung: X‑ray computed microtomography is a non-destructive imaging technique recognized in the geosciences as a powerful tool to investigate rock textures directly in three dimensions (3D) at the micrometer and sub-micrometer scale. The quantitative morphological and textural analysis of images requires segmentation and characterization of phases in the reconstructed volume based upon their gray levels (related to their relative X‑ray attenuation) and/or morphological aspects. Often the differences in X‑ray attenuation of some phases are so small that no contrast is observed in the reconstructed slices or, although the human eye can discern the differences between these phases, it is difficult, or sometimes impossible, to reliably segment and separately analyze these phases. Facing this challenge, we propose an experimental and computational procedure that allows the segmentation of phases with small density variations in geomaterials. By using an experimental protocol based on phase-contrast synchrotron X‑ray microtomography combined with a customized 3D image processing procedure, we successfully segmented feldspar from the glassy matrix in both a natural volcanic sample and a synthetic analog. Our results demonstrate that crystallized natural volcanic rocks and synthetic analogs can be characterized by synchrotron X‑ray phase-contrast microtomography and that phase-retrieval processing is an invaluable tool for the reconstruction of 3D multiphase textures.
    Beschreibung: Elettra- proposal no. 20120015
    Beschreibung: Published
    Beschreibung: 2301–2311
    Beschreibung: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Beschreibung: JCR Journal
    Schlagwort(e): Synchrotron X‑ray microtomography ; Phase-contrast X‑ray imaging ; Phase-retrieval ; 3D rock textures ; Crystallization ; Feldspars ; Synchrotron X-ray microtomographic images of crystallized natural magmas
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 8
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    Volatile segregation and generation of highly vesiculated explosive magmas by volatile-melt fining processes: The case of the Campanian Ignimbrite eruption (2020)
    Elsevier
    Details
    Publikationsdatum: 2021-09-03
    Beschreibung: 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.
    Beschreibung: Published
    Beschreibung: 1-14
    Beschreibung: 4V. Processi pre-eruttivi
    Beschreibung: JCR Journal
    Schlagwort(e): Ignimbrite ; Extremely dilute pyroclastic density currents ; Magmatic volatiles ; Fluxing ; Chromatographic separation
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 9
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    Dendritic crystallization in hydrous basaltic magmas controls magma mobility within the Earth's crust (2022)
    Nature PG
    Details
    Publikationsdatum: 2022-07-07
    Beschreibung: The majority of basaltic magmas stall in the Earth's crust as a result of the rheological evolution caused by crystallization during transport. However, the relationships between crystallinity, rheology and eruptibility remain uncertain because it is difficult to observe dynamic magma crystallization in real time. Here, we present in-situ 4D data for crystal growth kinetics and the textural evolution of pyroxene during crystallization of trachybasaltic magmas in high-temperature experiments under water-saturated conditions at crustal pressures. We observe dendritic growth of pyroxene on initially euhedral cores, and a surprisingly rapid increase in crystal fraction and aspect ratio at undercooling ≥30 °C. Rapid dendritic crystallization favours a rheological transition from Newtonian to non-Newtonian behaviour within minutes. We use a numerical model to quantify the impact of rapid dendritic crystallization on basaltic dike propagation, and demonstrate its dramatic effect on magma mobility and eruptibility. Our results provide insights into the processes that control whether intrusions lead to eruption or not.
    Beschreibung: Published
    Beschreibung: 3354
    Beschreibung: 5V. Processi eruttivi e post-eruttivi
    Beschreibung: JCR Journal
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 10
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    Role of volatiles in highly explosive basaltic eruptions (2022)
    Nature PG
    Details
    Publikationsdatum: 2022-07-07
    Beschreibung: Water and carbon dioxide are the most abundant volatile components in terrestrial magmas. As they exsolve into magmatic vapour, they promote magma buoyancy, accelerating ascent and modulating eruptive dynamics. It is commonly thought that an increase in pre-eruptive volatile content produces an increase in eruption intensity. Using a conduit model for basaltic eruptions, covering the upper 6 km of conduit, we show that for the same chamber conditions mass eruption rate is not affected by CO2 content, whereas an increase in H2O up to 10 wt.% produces an increase in eruption rate of an order of magnitude. It is only when CO2 is injected in the magma reservoir from an external source that the resulting pressurisation will generate a strong increase in eruption rate. Results also show that ascent velocity and fragmentation depth are strongly affected by pre-eruptive volatile contents demonstrating a link between volatile content and eruptive style.
    Beschreibung: Published
    Beschreibung: 156
    Beschreibung: 5V. Processi eruttivi e post-eruttivi
    Beschreibung: JCR Journal
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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