Settembre 2021

PubAIV 2021
(aggiornamento Settembre 2021)

1) Magmi e sistemi di alimentazione (3 articoli)
2) Dinamiche eruttive e di messa in posto (5 articoli)
3) Geologia e struttura dei vulcani (2 articoli)
4) Monitoraggio, pericolosità e rischio vulcanico (2 articoli)

Tematica 1: Magmi e sistemi di alimentazione
Caracciolo A., Kahl M., Bali E., Guðfinnsson G.H., Halldórsson S.A., Hartley M.E. (2021)
Timescales of crystal mush mobilization in the Bárðarbunga-Veiðivötn volcanic system based on olivine diffusion chronometry.
American Mineralogist, 106(7), 1083-1096
Data di pubblicazione: 01/07/2021
PubAIV-ID-00017 - Articolo in Rivista (non-open access)

The timescales of magmatic processes within a volcanic system may be variable over a volcano’s geological history. Crystals reflect environmental perturbations under which they grew, and compositional gradients quenched inside crystals on eruption can be exploited to extract timescales of magmatic processes. Here, we use multi-element diffusion chronometry in olivine macrocrysts to recover their residence time in a melt that ultimately erupted at the surface. The macrocrysts were mobilized by the carrier melt from mushy layers in the magma reservoir, and diffusion timescales likely reflect the time interval between mush disaggregation, ascent, and eruption. To unravel the evolution of mush disaggregation timescales with time, we target early-Holocene, middle-Holocene, and historical magmatic units erupted in the Bárðarbunga-Veiðivötn volcanic system in Iceland’s Eastern Volcanic Zone. Macrocryst contents vary between samples; early-Holocene samples are highly phyric (10–45 vol% macrocrysts) and contain gabbroic nodules, whereas middle-Holocene (5–15 vol%) and historical units (5–10 vol%) tend to be generally less phyric. Early-Holocene olivine macrocrysts have core compositions in the range Fo84–87, while middle-Holocene and historical samples record a wider range in core compositions from Fo80 to Fo86.5. Olivine rims are in chemical equilibrium with their carrier liquid and are slightly more evolved in early-Holocene units (Fo76–81) compared to middle-Holocene (Fo78–80) and historical (Fo81–83) units. Diffusion chronometry reveals that the timescale between mush dis-aggregation and eruption has changed over time, with timescales getting shorter approaching recent times. Early-Holocene olivine macrocrysts dominantly record Fe-Mg diffusion timescales between 200–400 days, while middle-Holocene and historical units typically record timescales of about 70 and 60 days, respectively. Barometric studies suggest that melts and crystals are likely stored and gradually transferred throughout an interconnected multi-tiered system that ultimately culminates in a mid-crustal reservoir(s) at about 6.8–7.5 ± 2.5 km depth, where final disaggregation by the carrier liquid took place. We argue that, as a result of extensional processes enhanced by rifting events, well-mixed melts got drawn into mid-crustal reservoir(s), causing crystal mush loosening and mobilization. In addition, we propose that more energy in the form of heat and/or melt supply was required in the early-Holocene to break up the dense mush fabric and convert it into an eruptible magma. Conversely, as evidenced by the diverse macrocryst content of the historical units and by the lack of gabbroic nodules, the system has become characterized by a less compact mush fabric since at least the middle-Holocene, such that fresh injection of melt would easily loosen and mobilize the mush, resulting in an eruption within a couple of months. This study provides evidence that along axial rift settings, rifting-related processes can help to “pull the mush apart” with no requirement for primitive magma injection as an eruption trigger. Furthermore, we provide evidence that in the Bárðarbunga-Veiðivötn volcanic system specifically, the time between mush disaggregation and eruption has decreased considerably with time, indicating shorter warning times before imminent eruptions.
Fedele L., Cole P.D., Scarpati C., Robertson R.E.A. (2021)
Petrological insights on the last 1000 years of explosive activity at La Soufrière volcano, St. Vincent (Lesser Antilles).
Lithos, 392–393, 106150
Data di pubblicazione: 03/04/2021
PubAIV-ID-00015 - Articolo in Rivista (non-open access)

The petrological features of scoria samples and enclosed holocrystalline xenoliths fromthe last ~1000 years of activity of the La Soufrière volcano of St. Vincent (Lesser Antilles) are described in detail here. The products of the investigated prehistoric eruptions (pre-1440, 1440, 1580 CE) are relatively homogeneous basaltic andesites (with a paragenesis consisting of plagioclase, clinopyroxene, orthopyroxene and opaques) commonly hosting gabbroic xenoliths. Scoria samples fromthe historical eruptions (1718–1812 and 1902–03 CE) are mostly similar to the former in terms of whole-rock composition, mineral chemistry and types of xenoliths, but include also a mafic-rich scoria type (plagioclase + clinopyroxene + olivine) in the products of the 1902–03 eruption that is
less evolved in composition and encloses ol-gabbro and ultramafic xenoliths. Both scoria types were likely affected by crystal contamination and accumulation processes, as indicated by their moderately to strongly porphyritic textures and large compositional variation of the crystal populations. Recycling of xenocryst,
protocryst and/or antecryst phases, however, did not significantly modify the original magma composition, as suggested by the overall consistency of whole-rock differentiation trends with petrography, mineral chemistry, xenolith types and glass compositions (within both inclusions and the groundmass) and experimental petrology observations, crystal fractionation therefore still appearing as the main evolutionary process. Most of the gabbro and ol-gabbro xenoliths have mineral compositions in line with that of the coexisting phenocrysts and textural
features consistent with an intrusive origin, i.e., representing fully-crystallised melt aliquots. Conversely, ultramafic, troctolitic and noritic xenoliths (plus some ol-gabbro) are likely representing cumulitic assemblages, i.e., mineral phases removed from the magma by crystal fractionation. The typical association of An-rich plagioclase and relatively Fo-poor olivine of the troctolite (and ol-gabbro) cumulates is ascribed to crystallisation from a hydrous (H2O ~4.5–6 wt%) high-Al2O3 basalt/basaltic andesite magma crystallising at shallow depths (~0.2 GPa,
i.e., at ~7 km). On the other hand, the ultramafic cumulitic xenoliths are thought to derive from a less hydrous basalt magma stalling at deeper levels (~0.4 GPa, ~13 km). The tapping of such magma could mark a major rejuvenation event, which is the process that likely triggered the 1902–03 eruption.
Giuffrida M., Scandura M., Costa G., Zuccarello F., Sciotto M., Cannata A., Viccaro M. (2021)
Tracking the summit activity of Mt. Etna volcano between July 2019 and January 2020 by integrating petrological and geophysical data.
Journal of Volcanology and Geothermal Research, 418, 107350
Data di pubblicazione: 18/07/2021
PubAIV-ID-00016 - Articolo in Rivista (non-open access)

The evolution of volcanic activity observed at the New South East Crater (NSEC) and Voragine (VOR) between July 2019 and January 2020 has been deciphered by taking into account the changes of textures and chemical zoning of plagioclase and olivine crystals from the erupted lavas and tephra. The petrological observations have been integrated with analyses of the amplitude and source location of volcanic tremor and infrasound data. Characteristics of crystals erupted on July 2019 at the NSEC reflect protracted intrusions of magma into the mid-upper section of the plumbing system, approximately within 290–120 MPa, which acted as the main zone of magma accumulation and crystallization before the beginning of the eruptive activity. Textures and compositions of crystals erupted at VOR emphasize the beginning of volcanic activity driven by recharge/discharge phases that mostly affect the shallowest portion of the Mt. Etna plumbing system (<40 MPa). At the end of 2019, mineral compositions and zoning patterns changed again in accordance with eruption dynamics. The observed changes reflect the transition from an early phase, between November and December 2019, characterized by substantial equilibrium during magma storage and transport toward higher disequilibrium conditions and eruptive frequency, in January 2020. This has been associated to episodes of deep replenishment of mafic magmas displacing the resident one. Diffusion chronometry applied to zoned olivines shows that most of the episodes of magma intrusion correlate temporally with changes in the features of both volcanic tremor and infrasonic events in terms of amplitude and source location, providing evidence that such geophysical signals are directly related to the magma dynamics in the upper plumbing system.
Tematica 2: Dinamiche eruttive e di messa in posto
Andronico D., Cannata A., Di Grazia G., Ferrari, F. (2021) 
The 1986–2021 paroxysmal episodes at the summit craters of Mt. Etna: Insights into volcano dynamics and hazard. 
Earth-Science Reviews, 220, 103686
Data di pubblicazione: 18/05/2021
PubAIV-ID-00018 - Articolo in Rivista (non-open access)

Despite Mt. Etna's long-standing reputation as an effusive volcano, since 1986 there has been an evident increase in mid-intensity explosive eruptions from its summit craters, with more than 240 episodes, better known as paroxysms (otherwise called paroxysmal episodes). These are characterized by strong Strombolian to lava fountaining activity that lasts from tens of minutes to a few days, producing some km-high volcanic plumes and tephra fallouts up to hundreds of km on the ground. Most paroxysms give life to sequences which are clustered like “episodic” eruptions for periods of a few days to a few months, their frequent recurrence causing hazard to air traffic and impacting densely inhabited areas. Nonetheless, a list containing the dates and data of these eruptions is lacking. In this paper, we tried to fill this gap by compiling a complete record, including master data (date, crater), eruption style and seismic parameters for identifying, characterizing and quantifying both the individual episodes and the entire period. This information comes from a critical review of surveillance reports, raw-data analysis and scientific literature. A retrieval of homogenous and comparable seismic data was possible only for episodes after 2006 following the renewal of seismic stations. The eruption list provides a complete picture of the 1986–2021 paroxysms, allowing to evaluate their temporal distribution, make a statistical analysis of their time-interval, and undertake a comprehensive investigation of the features of volcanic tremor. The results show a high probability (72%) of having a paroxysmal episode in the 10 days following the previous one. Moreover, a scaling relationship associated with the number-size distribution of the amplitude increases of volcanic tremor accompanying the explosive activities has been constrained. During sequences of paroxysms, combining these outputs can help improve the hazard assessment in terms of frequency of the associated tephra fallouts, and predict the duration of the entire sequence.
Giordano G., De Astis G. (2021)
The summer 2019 basaltic Vulcanian eruptions (paroxysms) of Stromboli.
Bulletin of Volcanology 83, 1
Data di pubblicazione: 10/01/2021
PubAIV-ID-00025 - Articolo in Rivista (open access)

Stromboli is an active, open conduit mafic volcano, whose persistent mild Strombolian activity is occasionally punctuated by much stronger explosions, known as paroxysms. During summer 2019, the volcano unexpectedly produced one such paroxysm on July 3, followed by intense explosive and intermittent effusive activity culminating in a second paroxysm on August 28.
Visual observations and the analysis of the fall deposits associated with the two paroxysms allowed us to reconstruct ballistic exit velocities of up to 160 m s−1. Plume heights of ~ 8.4 km and 6.4 km estimated for the two events correspond to mass eruption rates of 1.1 × 106 kg s−1 and 3.6 × 105 kg s−1, respectively. This is certainly an underestimate as directional pyroclastic flows into
which mass was partitioned immediately formed, triggering small tsunamis at the sea entrance. The mass of ballistic spatters and blocks erupted during the July 3 event formed a continuous cover at the summit of the volcano, with a mass calculated at ~ 1.4 × 10^8 kg. The distribution of fall deposits of both the July 3 and August 28 events suggests that pyroclasts characterized by terminal
fall velocities < 10–20 m s−1 remained fully suspended within the convective region of the plume and did not fall at distances closer than ca 1700 m to the vent. Based on the impulsive, blast-like phenomenology of paroxysms as well as the deposit distribution and type, paroxysms are classified as basaltic Vulcanian in style. The evolution of the summer 2019 eruptive events was not properly captured within the framework of the alert level system which is focused on tsunamigenic processes, and this is discussed so as to provide elements for the implementation of the reference scenarios and an upgrade of the system to take into account such events. In particular we find that, although still largely unpredictable, at least at operational time scales, and not necessarily tsunamigenic, Vulcanian eruptions and the subsequent evolution of the eruptive phenomena should be considered for the alert level system. This serves as a warning to the implementation of alert systems where the unexpected needs to be taken into account, even at systems that are believed to be relatively “predictable” as is the case at many persistently active, open vent mafic systems.
Giordano G., Cas R.A.F. (2021)
Classification of ignimbrites and their eruptions.
Earth-Science Reviews 220, 103697
Data di pubblicazione: 01/06/2021
PubAIV-ID-00026 - Articolo in Rivista (non-open access)

The term “ignimbrite” probably encompasses the one of the largest ranges of deposit types on Earth, associated with the partial to total collapse of explosive eruption columns feeding pyroclastic density currents. Surprisingly, there is no quantified classification scheme for ignimbrite types, as there is for fallout deposits, and this is a remarkable deficiency of modern volcanology. This has so far prevented the identification of standardized descriptors for ignimbrites and the improvement of methods for the documentation of their characteristics, such as happened for fallout deposits, building on the classification scheme proposed by Walker in 1973. Despite some earlier attempts, ignimbrite types do not conform to eruption style nomenclature. In this paper, we explore and discuss descriptors for a classification scheme based on the correlation of runout, areal extent, aspect ratio and volume from a compiled database comprising 92 ignimbrites, which then allows current understanding of pyroclastic flow dynamics to be considered. We refer to single ignimbrite outflow units, i.e. emplaced without significant breaks in their sedimentation, in extra-caldera settings and forming individual cooling units, irrespective of internal lithofacies architecture. Our main finding is that ignimbrites show remarkable power-law relationship between dispersal area/equivalent runout and bulk volume. Runout is directly related to increasing mass flow rate feeding the pyroclastic current. Volume is related to the magnitude of the flow event. We therefore propose that by measuring first order field observables such as bulk volume and dispersal area provides the opportunity to evaluate magnitude and intensity of related pyroclastic currents and, for large eruptions dominated by ignimbrites, of the eruption. Based on the relationships identified we propose that ignimbrites that originated from the collapse of single point-source eruption columns, usually smaller than 1 km3, are named “Vulcanian ignimbrites” and “Plinian ignimbrites” depending on the style of the eruption they are associated with. Larger ignimbrites that originated from caldera-forming eruptions along ring-fault fissure vents should be regarded as related to a separate eruption style - with respect to the common Hawaiian-Plinian trend -, where the effect of increased mass flow rate due to ring-fissure vents is dominant and controls the dynamics of the resulting collapsing fountains and pyroclastic flows, irrespective of the kind of eruption style that preceded the onset of the caldera collapse. These are named “caldera-forming ignimbrites” and are further subdivided into small, intermediate, large and super, based on their increasing erupted volume.
Spina L., Del Bello E., Ricci T., Taddeucci J., Scarlato P. (2021) 
Multi-parametric characterization of explosive activity at Batu Tara Volcano (Flores Sea, Indonesia)
Journal of Volcanology and Geothermal Research, 413, 107199
Data di pubblicazione: 18/02/2021
PubAIV-ID-00022 - Articolo in Rivista (non-open access)

Batu Tara is an active but poorly studied volcano located in the Lesser Sunda Archipelago (Indonesia). Its last known long-lasting eruptive phase, dating 2006–2015, was characterised by frequent short-lived explosions, similar in style and magnitude to those of the well monitored Stromboli volcano (Italy). On September 2014, we collected high-frequency multi-parametric measurements of the ongoing explosive activity to investigate the dynamics of intermediate-size volcanic explosions. We acquired synchronized acoustic, thermal and visible high-speed imaging data, and parameterized different spatial and temporal properties of each explosive event: i) maximum height and ejection velocity of bombs and plumes, ii) duration, iii) amplitude of acoustic and thermal transients, iv) acoustic and thermal energy, v) spectral features of the acoustic signals. The latter ones justify the assumption of a pipe resonance of the uppermost conduit section, likely in response to the arrival of over-pressurized gas at the free magma surface. The variability of the investigated parameters agrees with previous observations of intermediate-size explosions at other volcanoes, reflecting the complexity of the related source processes.
Stabile P., Arzilli F., Carroll M.R. (2021)
Crystallization of peralkaline rhyolitic magmas: pre- and syn-eruptive conditions of the Pantelleria system.
Comptes Rendus. Géoscience, 353, 1-20
Data di pubblicazione: 05/08/2021
PubAIV-ID-00023 - Articolo in Rivista (open access)

Pantelleritic magmas are low-viscosity peralkaline rhyolites which exhibit large differences in eruptive style (explosive to effusive). The processes that promote fragmentation and explosive eruptions of pantelleritic magma remain subject to debate, but undoubtedly variations of magma viscosity during magma ascent and degassing contribute to differences in eruptive style. Because crystallization can significantly influence magma rheology, we present a review of equilibrium and disequilibrium crystallization experiments of pantellerites, focusing on the crystallization of the main phases, alkali feldspar, and (lesser) clinopyroxene. Our analysis of data for several explosive pantelleritic eruptions on Pantelleria suggests pre-eruptive pressures of 50–100 MPa, temperatures of 700–800 °C for water-saturated conditions. Given these conditions, we show that the low pre-eruptive crystal fractions (0.08 to 0.15), temperatures between 700 and 800 °C, and the decrease of melt H2O content during magma ascent/decompression can promote a significant change in viscosity (up to 106–107 Pa·s), leading to magma brittle fragmentation and explosive eruptions. Because of their typical range of viscosity, pantelleritic magmas may show greater variations in eruptive style due to differences in ascent (decompression) rate when compared with metaluminous rhyolites.
Tematica 3: Geologia e struttura dei vulcani
Cannata A., Iozzia A., Alparone S., Bonforte A., Cannavò F., Cesca S., Gresta S., Rivalta E., Ursino A. (2021) 
Repeating earthquakes and ground deformation reveal the structure and triggering mechanisms of the Pernicana fault, Mt. Etna. 
Communications Earth & Environment 2, 116
Data di pubblicazione: 09/06/2021
PubAIV-ID-00019 - Articolo in Rivista (open access)

Structure and dynamics of fault systems can be investigated using repeating earthquakes a repeatable seismic sources, alongside ground deformation measurements. Here we utilise a dataset of repeating earthquakes which occurred between 2000 and 2019 along the transtensive Pernicana fault system on the northeast flank of Mount Etna, Italy, to investigate the fault structure, as well as the triggering mechanisms of the seismicity. By grouping the repeating earthquakes into families and integrating the seismic data with GPS measurements of ground deformation, we identify four distinct portions of the fault. Each portion shows a different behaviour in terms of seismicity, repeating earthquakes and ground deformation, which we attribute to structural differences including a segmentation of the fault plane at depth. The recurrence intervals of repeating earthquake families display a low degree of regularity which suggests an episodic triggering mechanism, such as magma intrusion, rather than displacement under a constant stress.
Gambino S., Armienti P., Cannata A., Del Carlo P., Giudice G., Giuffrida G., Liuzzo M., Pompilio M. (2021) 
Chapter 7.3 Mount Melbourne and Mount Rittmann. 
Geological Society, London, Memoirs, 55(1), 741-758.
Data di pubblicazione: 01/01/2021
PubAIV-ID-00020 - Capitolo di un libro (non-open access)

Mount Melbourne and Mount Rittmann are quiescent, although potentially explosive, alkaline volcanoes located 100 km apart in Northern Victoria Land quite close to three stations (Mario Zucchelli Station, Gondwana and Jang Bogo). The earliest investigations on Mount Melbourne started at the end of the 1960s; Mount Rittmann was discovered during the 1988–89 Italian campaign and knowledge of it is more limited due to the extensive ice cover. The first geophysical observations at Mount Melbourne were set up in 1988 by the Italian National Antarctic Research Programme (PNRA), which has recently funded new volcanological, geochemical and geophysical investigations on both volcanoes. Mount Melbourne and Mount Rittmann are active, and are characterized by fumaroles that are fed by volcanic fluid; their seismicity shows typical volcano signals, such as long-period events and tremor. Slow deformative phases have been recognized in the Mount Melbourne summit area. Future implementation of monitoring systems would help to improve our knowledge and enable near-realtime data to be acquired in order to track the evolution of these volcanoes. This would prove extremely useful in volcanic risk mitigation, considering that both Mount Melbourne and Mount Rittmann are potentially capable of producing major explosive activity with a possible risk to large and distant communities.
Tematica 4: Monitoraggio, pericolosità e rischio vulcanico
Monaco L., Palladino D.M., Gaeta M., Marra F., Sottili G., Leicher N., Mannella G., Nomade S., Pereira A., Regattieri E., Wagner B., Zanchetta G., Albert P.G., Arienzo I., D’Antonio M., Petrosino P., Manning C.J., Giaccio B. (2021)
Mediterranean tephrostratigraphy and peri-Tyrrhenian explosive activity revaluated in light of the 430-365 ka record from Fucino Basin (central Italy).
Earth-Science Review 220, 103706
Data di pubblicazione: 21/09/2021
PubAIV-ID-00024 - Articolo in Rivista (open access)

Accurately reconstructing the scale and timing of dynamic processes, such as Middle-Late Pleistocene explosive volcanism and rapid climatice change, requires rigorous and independent chronological constraints. In this framework, the study of distal volcanic ash layers, or tephra, transported and deposited over wide regions during explosive volcanic eruptions, is increasingly being recognised as a fundamental chronostratigraphic tool for addressing these challenging issues. Here we present a high-resolution distal tephra record preserved in the lacustrine sedimentary succession of the Fucino Basin, central Italy. The investigated record spans the 430-365 ka time interval, covering the entirety of Marine Isotope Stage 11 (MIS 11), and provides important insights into peri-Tyrrhenian potassic explosive volcanism from sources located in central Italy against a backdrop of Mediterranean palaeooclimate records. The succession of ash fall events of this time interval is reconstructed through a detailed lithostratigraphic, geochemical and 40Ar/39Ar geochronological characterization of the deposits preserved as discrete layers in the Fucino F4-F5 sediment core. This work is complemented by similarily detailed characterization of selected proximal pyroclastic units from the peri-Tyrrhenian potassic volcanoes. Geochemical fingerprinting of the tephra deposits by means of their major, minor and trace elements and Sr isotope compositions indicates that all the thirty-two investigated ash layers derived from the peri-Tyrrhenian potassic volcanoes. The stratigraphically continuous succession of the Fucino tephra layers allowed the development of a fully independent, 40Ar/39Ar age-constrained, Bayesian age-depth model for the investigated time interval. The age-model allows us to establish modelled ages for the tephra layers within the succession that are not directly dated. The resulting dated tephra record clearly reveals a highly time resolved and previously unparalelled chronicle of explosive activity from the Vulsini, Vico, Sabatini, Colli Albani and Roccamonfina volcanic complexes. Our study provides a benchmark and valuable geochemical and geochronological dataset to be used as a reference for any future development and application of the tephrostratigraphic methods across the central Mediterranean area both during the investigated 430-365 kyr time interval, and deeper in time. This contribution underlines the importance of integrating proximal and distal sedimentary records to more accurately establish long-term and comprehensive volcanic eruption records.
Re G., Corsaro R.A., D'Oriano C., Pompilio M. (2021)
Petrological monitoring of active volcanoes: A review of existing procedures to achieve best practices and operative protocols during eruptions.
Journal of Volcanology and Geothermal Research, 419, 107365
Data di pubblicazione: 30/07/2021
PubAIV-ID-00021 - Articolo in Rivista (non-open access)

A questionnaire to survey the common petrological monitoring procedures adopted by volcano monitoring institutions has been developed, aimed at identifying prevailing techniques and rating their suitability in terms of costs versus benefits. The collected information resulted from a sample of eighteen participating institutions, which include countries with some of the most important active volcanic provinces worldwide. The participating institutions also offer insights into volcanoes with a variety of volcanic activity, providing a comprehensive picture of the state of the art of petrological monitoring. The final purposes are (i) to promote the advancement that petrologic monitoring brings in the comprehension of the eruptive processes, providing the only “signals” (i.e., rock samples) concerning the physico-chemical properties of the magma feeding the eruption; (ii) to design best practices, and (iii) to define the minimum requirements needed to perform an efficient petrological monitoring during ongoing eruptions. The survey also highlighted the main problems to overcome to have a profitable petrological monitoring infrastructure, including (i) the time required to accomplish both field survey and laboratory works (sampling, sample preparation, and analyses), (ii) the lack of onsite analytical facilities, (iii) the shortage of qualified staff.

Starting from the state of the art of petrological monitoring, how it is performed by the different institutions worldwide, and what participants considered as the major problems, we identified the Best Practices in Petrological Monitoring as the best compromise between fast and easy analyses and the relevance of the acquired results.
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