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Petrological studies of active volcanoes typically focus on eruptive phenomena occurring over long timescales of the order of days to years, aiming at identifying major changes in the physico-chemical state of magma during ascent towards the surface. Exceptionally, we present results from an integrated petrological and statistical approach based on the compilation of ∼5300 major and trace element data for glass and crystals, in combination with volcanological data on eruptive events occurred over timescales of minutes at Stromboli volcano (Sicily). On May 11, 2019, we had the rare opportunity to collect individual fresh fallout ash products from eighteen mostly consecutive explosions, erupted in a 2-h time span and, at the same time, to acquire continuous high frequency (50 Hz) infrared thermal data of the same explosions. Through video analysis, we observe that explosions were more frequent and ash-dominated at the southwestern crater area (SCA, 8–10 events/h) than at the northeastern crater area (NCA, 3–5 events/h), where coarser material was ejected. The statistical analysis of glass and plagioclase compositions reveals differences in the products erupted from the two crater areas. SCA explosions tapped less differentiated magmas (Mg#∼42–46, ∼257–365 LaN, ∼0.7–0.9 Eu/Eu*) in equilibrium with more anorthitic plagioclase cores (An∼72–88), whereas NCA area explosions are more differentiated (Mg#∼40–44, ∼286–387 LaN, ∼0.6–0.8 Eu/Eu*) and in equilibrium with less anorthitic plagioclase cores (An∼68–82). Thermometric calculations based on major and trace element clinopyroxene-plagioclase-melt equilibrium modeling highlight that the SCA explosions were statistically fed by hotter magmas in comparison to NCA explosions. Plagioclase-based diffusion modeling also indicates longer timescales for the dynamic ascent of NCA magmas, leading to preferential groundmass crystallization at the conduit walls and transition from sideromelane to tachylite groundmass textures. The final emerging picture is that in May 2019, concurrent normal eruptions from different crater areas at Stromboli were heralds of compositionally and thermally diverse magmas rising at different rates within the uppermost branched part of the conduit region. High frequency petrological investigations aided by statistical treatment of data have the potential to constrain dynamic conduit processes related to transient, explosive eruptions in persistently active volcanoes, thereby offering new insights on the interplay between magma dynamics, ascent timescales, and eruptive behavior. ISSN:0024-4937

Basaltic volcanoes can remain active for tens to thousands of years with the continual presence of magma, requiring storage and transport conditions that can sustain persistently eruptible melt. Magma storage conditions beneath these volcanoes may significantly change with time, leading to sudden and dramatic changes in explosivity. Determining the rates and causes of these changes and how they modulate eruptive style over societally relevant timescales is of paramount importance for evaluating potential hazards. In June-August 2019, one major explosion and two paroxysms occurred at Stromboli volcano (Southern Italy) within only 64 days offering a unique opportunity to study the short-term variations in a basaltic plumbing system that can lead to paroxysmal events.Stromboli is an active open conduit basaltic volcano well-known for its persistent mild (normal) Strombolian activity occasionally interrupted by sudden, short-lived events ranging in size and intensity from major (violent Strombolian) to paroxysmal explosions. Strombolian activity, effusive eruptions and major explosions, all involve a degassed, highly porphyritic (hp) magma from a shallow reservoir. Deep-seated more mafic and, volatile-rich low-porphyritic (lp) magma is erupted, alongside hp-magma, during paroxysms, and in smaller quantities during some of the major explosions. Both lp- and hp-magmas were erupted during the 3 July and 28 August 2019 paroxysms, whereas only hp-magma was erupted during the major explosion on 25 June 2019.Via a multifaceted approach using clinopyroxene from the summer 2019 paroxysms, we reveal a key role for batches of volatile-rich lp-magma recharge arriving in the shallow reservoir up to a few days before these events. Our data indicate a rejuvenated Stromboli plumbing system where the extant crystal mush is efficiently permeated by recharge lp-magma with minimum remobilisation promoting a direct linkage between the deeper (lp) and shallow (hp) reservoirs. This sustains the current variability of eruptive styles with near immediate eruptive response to mafic magma recharge. The remarkable agreement between our calculated recharge timescales and the observed variation in time of various monitoring signals strongly supports such a model.Our approach provides vital insights into magma dynamics and their effects on monitoring signals demonstrating that detailed petrological studies integrated with volcano monitoring signals are fundamental for a fast response during a volcanic unrest phase or crisis.This work has been published in Nature Communication: Petrone, C.M., Mollo, S., Gertisser, R. et al. Magma recharge and mush rejuvenation drive paroxysmal activity at Stromboli volcano. Nat Commun 13, 7717 (2022). https://doi.org/10.1038/s41467-022-35405-z.

Starting from February 2021, Mt. Etna (Italy) experienced a period of intense explosive activity with 17 lava fountain episodes between 16 February and 1 April 2021. During the eruptive cycle, the Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Etneo (INGV-OE) issued 62 alert notifications known as VONAs (Volcano Observatory Notice for Aviation) to inform the aeronautical authorities about the volcanic activity. We present an automated VONA-based workflow aimed at real-time assessment of the volcanic hazard due to tephra fallout at Mt. Etna. When a VONA reporting tephra emission is issued by INGV-OE, numerical simulations accounting for atmospheric and eruptive uncertainties are automatically initialized to produce probabilistic hazard maps of tephra fallout and atmospheric dispersal. We applied the workflow to three lava fountains that occurred during the 2021 eruptive cycle. To test the modelling results, we compared the simulated ground load with field data, and the extent and position of the simulated volcanic cloud with the observed or estimated volcanic cloud from the Toulouse Volcanic Ash Advisory Center. Overall, we found a good match between simulated and observed quantities (tephra loads and volcanic cloud position), especially when accurate information on eruptive conditions (column height and duration) are supplied by the VONAs. Finally, through a statistical analysis, we found that column height and wind field are fundamental in determining tephra ground accumulation. For this reason, these parameters should be constrained by observational data as accurately as possible when performing numerical simulations, especially in the line of developing operational workflows., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Volcanic hazards associated with lava flows advancing on a snow cover are often underrated. On 16 March 2017, during a mild effusive-explosive eruption at Mt Etna (Italy) a slowly advancing lava lobe interacted with the snow cover producing a sudden, short-lasting sequence of explosions. White vapor, brown ash and coarse material were suddenly ejected, and the products hit a group of people, injuring some of them. The proximal deposit formed a continuous mantle of ash, lapilli and decimetric-sized bombs, and the ballistic material reached up to 200 meters away from the lava edge. A total deposit mass of 7.1 ± 0.8 × 104 kg was estimated, corresponding to a lava volume removed by the explosion of 32.0 ± 3.6 m3. Textural and morphological data on the ejected clasts were used to constrain a model of lava-snow interaction. Results suggest that the mechanism responsible for the explosions was the progressive pressure build-up due to vapor accumulation under the lava flow, while no evidence was found for the occurrence of fuel-coolant interaction processes driving the explosions. Although these low-intensity explosions are not too frequent, the collected data represent a unique dataset which provides useful information on the involved processes and the associated hazard, but also on possible measures of mitigation to prevent potentially dramatic accidents at volcanoes like Etna, recording up to thousands of visitors per day.

The eruption of basaltic magmas dominates explosive volcanism on Earth and other planets within the Solar System. The mechanism through which continuous magma fragments into volcanic particles is central in governing eruption dynamics and the ensuing hazards. However, the mechanism of fragmentation of basaltic magmas is still disputed, with both viscous and brittle mechanisms having been proposed. Here we carry out textural analysis of the products of ten eruptions from seven volcanoes by scanning electron microscopy. We find broken crystals surrounded by intact glass that testify to the brittle fragmentation of basaltic magmas during explosive activity worldwide. We then replicated the natural textures of broken crystals in laboratory experiments where variably crystallized basaltic melt was fragmented by rapid deformation. The experiments reveal that crystals are broken by the propagation of a network of fractures through magma, and that afterwards the fractures heal by viscous flow of the melt. Fracturing and healing affect gas mobility, stress distribution, and bubble and crystal size distributions in magma. Our results challenge the idea that the grain size distribution of basaltic eruption products reflects the density of fractures that initially fragmented the magma and ultimately indicate that brittle fracturing and viscous healing of magma may underlie basaltic explosive eruptions globally. In explosive basaltic eruptions, brittle fragmentation and subsequent healing by viscous melt are documented by textural analysis of products from ten disparate eruptions, suggesting that grain size may not reflect the initial fracture density of magma.

A variety of eruptive styles concurred to define the explosive activity of the 2021 Cumbre Vieja eruption (La Palma, Canary Islands, Spain). These styles include, as broadly defined, lava fountaining, Strombolian explosions, rapid Strombolian, spattering, ash-rich jets, and ash venting, and occurred both alternately and simultaneously at the multiple vents that hosted the activity during the more-than-three-months-long eruption. In order to capture the defining features and the underlying processes of these styles and of their transitions, we deployed FAMoUS (Fast, MUltiparametric Setup) during two field campaigns, between 22 September-1 October and between 5-9 November 2021. FAMoUS includes one high-speed camera (frame rate 250 to 500 frames per second (FPS) and 0.021-0.147 m/pixel resolution at the vent), one thermal camera (up to 50 FPS and 0.2-0.8 m/pixel .ca), three high-definition cameras (25 FPS, 0.03-1.2 m/pixel ca.), and one microphone (flat response between 0.5 and 10000 Hz, sampling rate 20 kHz). Preliminary video processing results, obtained using both manual tracking and Optical Flow routines, reveal ejection velocities of pyroclasts in the 20-220 m/s range, with the highest and the lowest values of peak velocity being recorded during Strombolian explosions and ash venting, respectively. All activity styles display ejection velocity fluctuations and variably marked ejection pulses, which are more pronounced during Strombolian explosions. Lava fountains feature the highest mean ejection velocity and a variety of fluctuation patterns, with larger-amplitude and more abrupt ones when transitioning towards Strombolian explosions. The maximum settling velocity of bomb-to lapilli-sized pyroclasts in the vicinity of the vent is remarkably stable around 50 m/s. The transition between the different styles of activity is marked by changing rates of ejection pulse frequency/amplitude and relative proportions of ash and bombs, pointing to a feedback between the volume, ascent rate, and frequency of gas pockets rising in the conduit, and the changes induced by their transit through the magma residing in the uppermost termination of the conduit.

The eruption of fragmental magma of basaltic composition is the most frequent type of explosive volcanism on Earth and in the Solar System, with eruptions spanning from centuries of persistent, weak explosions, through days to months of lava fountains and ash emissions, to rare, global-scale catastrophic events. The mechanism through which continuous magma fragments into volcanic particles is central in governing eruption dynamics and the ensuing hazards. However, the mechanism of fragmentation of basaltic magmas is still disputed, with both viscous and brittle mechanisms having been proposed for different eruptive styles. Here we carry out textural analysis of the products of ten eruptions from seven volcanoes by Scanning Electron Microscope. We find broken crystals surrounded by intact glass and other features that testify to the brittle fragmentation of basaltic magmas during explosive activity differing in style, intensity and magnitude. We then replicated the natural textures of broken crystals in laboratory experiments where variably crystallised basaltic melt was fragmented by rapid deformation. The experiments reveal that crystals are broken by the propagation of a network of fractures through magma, and that afterwards many of the fractures heal by viscous flow of the melt. Fracturing and healing affect gas mobility, stress distribution, and bubble and crystal size distributions in magma. Our results challenge the idea that the grain size distribution of basaltic eruption products reflects the density of the fractures that initially fragmented the magma. Unrecognised broken crystals and accompanying textures appear in previous literature covering many eruptions spanning Hawaiian lava fountains, catastrophic Plinian events, and more. We conclude that brittle fragmentation and subsequent healing are not specific to some eruption style or pyroclast type, but are ubiquitous factors controlling basaltic explosive volcanism.

Between 19 September and 13 December 2021 (85 days), a flank eruption took place along the Cumbre Vieja ridge (La Palma Island), one of the most active volcanic centers of Canary Islands. The last 7000 years of Cumbre Vieja activity has been characterized by a combination of effusive and explosive eruptions. These generated both cinder cones and lava flows. The previous event occurred between October 26 and November 28, 1971 (eruption of Teneguía). The 2021 eruption was characterized by the alternate (and often simultaneous) emission of lava flows, lava fountains and tephra plumes along a ~1 km-length fissure consisting of about ten vents that built a cinder cone complex. The southern vents were mostly associated with the generation of tephra plumes and lava fountains, while the northern vents were mostly associated with the generation of lava flows. The ~12 km2 lava flow field on the west side of the island reached the sea on September 28, forming a new lava delta and interacting with sea water producing lava haze (i.e. laze). Even though tephra was sedimented all over La Palma and sometimes reached the neighboring islands, the cumulative tephra deposit is mostly elongated towards the southwest and the northeast due to the prevailing wind direction, reaching a maximum thickness southwest of the fissure. Both lava fountains and more explosive tephra plumes contributed to the formation of the tephra deposit. Tephra plumes were associated with variable intensity reaching a few kilometers of altitude (

On September 19, 2021, the Cumbre Vieja volcano (La Palma, Canary Islands) erupted after 50 years dormant; the last eruption occurred in 1971, forming the Teneguía cone. Historical volcanism on La Palma typically produces simultaneous explosive/effusive eruptions producing cinder cones, tephra deposits and lava flow fields. The 2021 eruption was characterized by almost continuous tephra emission along a ~ 1 km long fissure, with only a few phases of quiescence lasting no more than few hours. Up to ten explosive vents were active at different times, with eruptive styles ranging from ash-venting, powerful Strombolian activity and lava fountaining. These formed volcanic plumes occasionally reaching 6-7 km above the growing composite cone. Coeval lava flows with variable, but mostly high effusion rates accompanied the explosive activity. The eruption stopped after 85 days on December 13, 2021.Studying the textures and morphology of tephra deposits can help define and classify the explosive processes that dominated the rise of magma and its fragmentation. For this reason, from the onset of the eruption, tephra samples were collected daily. These samples represent airfall from the plume, and were collected at distances between 1 and 13 km from the new Cumbre Vieja cone. Samples were used to evaluate the mass load per square meter unit, together with grain-size analysis. During the study period, 87 samples were weighed, giving tephra mass loads between 0.10 kg/m2 and 79 kg/m2. These values can be used for estimating the total erupted tephra mass within the first period of the eruption. The grain-size distribution of samples was measured at half-phi steps by CAMSIZER (Retsch), and shows significant temporal variation in magma fragmentation and dispersal. This can be correlated to variations in plume height and eruption style.Componentry analysis on ash samples was performed to assess both style and changes in the explosive activity. Seventeen ash samples (22 September – 1 November) were sieved to separate the 0.25-0.5 mm fraction, which allows easier distinction of particle components. Four types of components were recognized: sideromelane, tachylite, lithics and free crystals, each one characterized by different morphological and textural features. During the opening phase, a high percentage of sideromelane was erupted, then over the following weeks an increase in both lithic particles and variations in morphological features of sideromelane fragments were observed. Fragmentation-related broken crystals within intact particles are also found.These preliminary results match the variability in eruption styles observed. They confirm that tephra studies may constitute a powerful tool for monitoring ongoing intense eruptions by helping to comprehend, together with other techniques, the evolution of eruption dynamics, magma processes, and magma level in volcanic conduits.

During September-December 2021, the Cumbre Vieja eruption (La Palma, Canary Islands) was characterised by simultaneous explosive and effusive activity (Longpré, 2021; Pankhurst et al., 2021). The eruption produced a ~200 m high complex pyroclastic cone (Romero et al., 2022). A series of syn-eruptive lateral collapses modified the edifice morphology and caused sporadic breaching towards the west-northwest, influencing the nature and distribution of eruptive hazards.We documented these destructive events using tremor and seismic data, as well as direct visual and thermal observations of the eruptive activity. In addition, UASs were used for aerial surveys and DEM generation in late September 2021. Field descriptions of the resulting deposits and stratigraphic sampling of tephra fallout were carried out in October and November 2021. Microanalysis of pyroclastic fragments included scanning electron microscope and electron microprobe for textural and compositional characterisation.Two classes of collapse events were observed: the first involved a substantial portion of the cone and led to its horseshoe scar morphology; the second mainly affected ramparts of pyroclasts that separated vents along the fissure. The largest breaching event, which occurred on September 25, was generated by a high eruption rate and associated rapid deposition of pyroclasts on a steep pre-eruptive surface. Smaller collapses resulted from rapid pyroclastic agglutination on the conduit/fissure.Some collapses triggered an immediate and substantial increase in the lava flux presumably through release of lava that has been stored in the vent and/or shallow plumbing system. The largest collapses produced lava flows up to 10 m thick which rafted decameter-sized chunks of the failed edifice. In some cases, these outpourings inundated residential areas. Collapses were sometimes followed by an increase in the eruption intensity, forming lava fountains up to several hundred metres in height; we infer these fountains resulted from unloading of the shallow plumbing system.The 2021 eruption of Cumbre Vieja volcano provides a rare opportunity to document recurrent, syn-eruptive collapses of the vent edifice during a cone-forming eruption, and to identify and characterise the hazards associated with this common type of activity. References:Longpré, M. A. (2021). Reactivation of Cumbre Vieja volcano. Science, 374(6572), 1197-1198. Doi: 10.1126/science.abm9423Pankhurst, et al. (2022). Rapid response petrology for the opening eruptive phase of the 2021 Cumbre Vieja eruption, La Palma, Canary Islands. Volcanica, 5(1), pp. 1–10. Doi: 10.30909/vol.05.01.0110.Romero et al. (2022). Volume and stratigraphy of the Cumbre Vieja 2021 eruption tephra fallout, La Palma Island. VMSG Virtual Annual Meeting, 10-12th January 2022, Manchester, United Kingdom.

Typically, petrological monitoring studies focus on comparing eruptive phenomena with textural and compositional features of eruptive products recovered over long term (days to years) sampling campaigns aiming at identifying major changes in the magmatic plumbing system and eruptive dynamics. However, as far as we are aware, there have been few attempts to combine whole rock, microchemical, and microtextural data with ground-based imaging of volcanic eruptions at high spatial (individual eruptive centers) and high temporal (minutes to hours) resolutions.Here, we present a high-resolution petrological investigation using as test site Stromboli volcano, one of the most active and intensely monitored open-conduit volcanoes in the world and an important benchmark in understanding the physico-chemical processes related to magma and conduit dynamics. Normal eruptive activity is dominated by frequent and intermittent low-energy explosions (6 events/hour on average), throwing jets of crystal-rich basaltic scoriae, gas and ash to heights th 2019, we recorded 5 hours of explosive activity and sampled individual fresh fallout ash products from eighteen explosions. Six products were erupted from the N1 vent, whereas twelve products were erupted from the S2 vent. Analysis of high speed (50 Hz) infrared videos revealed that explosive activity was more frequent at the S2 vent (8-10 events/hour) than at the N1 vent (3-5 events/hour). The explosion types were differently distributed at the two areas, with prevalent ejection of coarser material at the N1 vent and ash-dominated explosions being more frequent at the S2 vent. Thermometric and hygrometric calculations based on clinopyroxene-plagioclase-melt equilibria comparatively highlight that N1 eruptions were fed by a colder, more degassed, and differentiated magma relative to that feeding S2 eruptions. Diffusion modeling of Li concentration profiles in plagioclase also indicate longer timescales of magma degassing and ascent for N1 eruptions, possibly due to enhanced groundmass crystallization at conduit walls. The final emerging picture is that concurrent normal eruptions from distinct vent areas at Stromboli are heralds of distinct magma differentiation conditions within the uppermost part of the magma storage region, in close agreement with observed eruptive phenomena. This high-resolution approach has the potential to unequivocally constrain the processes driving transient, rapid, explosive eruptions in active volcanoes, thus offering new insights on the interplay between magma dynamics, ascent timescales, and eruptive behavior.

Tajogaite cone in the Cumbre Vieja ridge (La Palma, Canary Islands) erupted between 19 September and 13 December 2021. The tephra and lava sourced from the newly formed fissure rapidly built a pyroclastic cone. During the early days of eruption and after several small-scale landslides, the west flank of the edifice partially collapsed on 25 September, breaching the cone and emplacing a prominent raft-bearing lava flow. Our research combines direct observations, digital elevation models, thermal and visible imaging, and textural and compositional investigation of the explosive products to describe and characterize the edifice growth and collapse. The cone built over a steep slope (26°) and its failure occurred after an intense phase of lava fountaining (up to 30 m3 s−1) that produced rapid pyroclastic accumulation. We suggest that an increased magma supply, to an ascent rate of 0.30 m s−1, led to the rapid growth of the cone (at 2.4 × 106 m3 day−1). Simultaneously, the SW lava flow reactivated and formed a lava ‘seep’ that undercut the flank of the cone, triggering a lateral collapse via rotational rockslide that moved at minimum speeds of 34–70 m h−1. The lateral collapse formed a ~ 200 m wide scar, involving 5.5 × 106 m3 of material, and covered 1.17 km2 with decametric edifice portions and raft-bearing lava. The collapse produced a modest change in the vent geometry, but did not affect eruptive activity long term. A short pause in the eruption after the collapse may have been favored by rapid emptying of the shallower magma system, reducing ascent rates and increasing crystallization times. These results reveal the complex chain of events related to the growth and destruction of newly formed volcanic cones and highlight hazards when situated close to inhabited areas.

Stromboli (Italy) is a basaltic volcano characterized by persistent, mild strombolian activity, occasionally interrupted by lava effusion and more violent explosive events, named major explosions and paroxysms depending on their intensity and magnitude. The normal activity is fed by a shallow and degassed highly porphyritic (HP) shoshonitic basalt carrying about 50 vol.% crystals settled in a shoshonitic glassy matrix (K2O > 3.8 wt.%). The more energetic explosions erupt a deep, volatile-rich, low-porphyritic (LP) magma with 2O 2O wt.%) due to

In July and August 2019, two paroxysmal eruptions dramatically changed the morphology of the crater terrace that hosts the active vents of Stromboli volcano (Italy). Here, we document these morphological changes, by using 2259 UAS-derived photographs from eight surveys and Structure-from-Motion (SfM) photogrammetric techniques, resulting in 3D point clouds, orthomosaics, and digital surface models (DSMs) with resolution ranging from 8.1 to 12.4 cm/pixel. We focus on the morphological evolution of volcanic features and volume changes in the crater terrace and the upper part of the underlying slope (Sciara del Fuoco). We identify both crater terrace and lava field variations, with vents shifting up to 47 m and the accumulation of tephra deposits. The maximum elevation changes related to the two paroxysmal eruptions (in between May and September 2019) range from +41.4 to −26.4 m at the lava field and N crater area, respectively. Throughout September 2018–June 2020, the total volume change in the surveyed area was +447,335 m3. Despite Stromboli being one of the best-studied volcanoes worldwide, the UAS-based photogrammetry products of this study provide unprecedented high spatiotemporal resolution observations of its entire summit area, in a period when volcanic activity made the classic field inspections and helicopter overflights too risky. Routinely applied UAS operations represent an effective and evolving tool for volcanic hazard assessment and to support decision-makers involved in volcanic surveillance and civil protection operations.

In 2019, Stromboli volcano experienced one of the most violent eruptive crises in the last hundred years. Two paroxysmal explosions interrupted the ‘normal’ mild explosive activity during the tourist season. Here we integrate visual and field observations, textural and chemical data of eruptive products, and numerical simulations to analyze the eruptive patterns leading to the paroxysmal explosions. Heralded by 24 days of intensified normal activity and 45 min of lava outpouring, on 3 July a paroxysm ejected ~6 × 107 kg of bombs, lapilli and ash up to 6 km high, damaging the monitoring network and falling towards SW on the inhabited areas. Intensified activity continued until the less energetic, 28 August paroxysm, which dispersed tephra mainly towards NE. We argue that all paroxysms at Stromboli share a common pre-eruptive weeks-to months-long unrest phase, marking the perturbation of the magmatic system. Our analysis points to an urgent implementation of volcanic monitoring at Stromboli to detect such long-term precursors., Integrated field and laboratory investigations, and numerical simulations of the 2019 paroxysmal explosions at Stromboli volcano revealed that they were anticipated by a week-to-month-long destabilization in the normal volcanic activity, a pattern common to all paroxysms.

Volcanic activity at Mt. Etna in the last decade has mostly been manifested by sequences of short paroxysmal episodes characterised by powerful lava fountains and high eruption columns. On the 23 February 2013, an exceptionally intense episode occurred at the New South-East Crater, producing a fountain >800 m high (among the highest ever recorded at Etna) and a ~9 km eruption column that dispersed ash >400 km from the vent. Textural and petrographic analyses of lapilli revealed that magma erupted during the high-intensity phase is characterised by low microlite contents (

Fallout of ballistic blocks and bombs ejected from eruptive vents represents a well-known hazard in areas proximal to volcanoes (mostly  km from the vent). However, fallout of large clasts sedimenting from plume margins that extend to medial areas and have the potential to produce severe injuries to people and cause damage to infrastructure, is often overlooked. Recent eruptive events at Mount Etna (Italy) provide a clear example where large-clast fallout from plume margins (>5 cm) has posed a real threat both to the many visitors reaching the summit area and to local infrastructure, and, therefore, has been selected as a case study. To quantify this hazard, a new particle sedimentation model was calibrated with field data and then used for probabilistic hazard assessments. For a fully probabilistic scenario the hazard zone covered 72 km2 and included some 125 km of paths and roads, as well as 15 buildings. Evacuation on foot to a safe area was estimated at almost 4 h, but this could be reduced to less than 3 h if two shelters were provided. Our results show the importance of integrating probabilistic hazard analysis of large-clast fallout within effective strategies of risk management and reduction, especially in the case of volcanoes where visitors can reach the summit areas.

Funder: VUB Strategic Research Program, Exposure to volcanic ash is a long-standing health concern for people living near active volcanoes and in distal urban areas. During transport and deposition, ash is subjected to various physicochemical processes that may change its surface composition and, consequently, bioreactivity. One such process is the interaction with anthropogenic pollutants; however, the potential for adsorbed, deleterious organic compounds to directly impact human health is unknown. We use an in vitro bioanalytical approach to screen for the presence of organic compounds of toxicological concern on ash surfaces and assess their biological potency. These compounds include polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dlPCBs). Analysis of ash collected in or near urbanised areas at five active volcanoes across the world (Etna, Italy; Fuego, Guatemala; Kelud, Indonesia; Sakurajima, Japan; Tungurahua, Ecuador) using the bioassay inferred the presence of such compounds on all samples. A relatively low response to PCDD/Fs and the absence of a dlPCBs response in the bioassay suggest that the measured activity is dominated by PAHs and PAH-like compounds. This study is the first to demonstrate a biological potency of organic pollutants associated with volcanic ash particles. According to our estimations, they are present in quantities below recommended exposure limits and likely pose a low direct concern for human health.

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.

The resuspension of volcanic ash by wind is a significant source of hazard during and after volcanic eruptions. Parameterizing and modeling ash resuspension requires direct measurement of the minimum wind shear stress required to move particles, usually expressed as the threshold friction velocity U ⁎ th, a parameter that, for volcanic ash, has been measured only scarcely and always in the laboratory. Here, we report the first field measurements of U ⁎ th for volcanic ash, with a portable wind tunnel specifically developed, calibrated, and tested. Field measurements, performed on natural reworked ash deposits from Sakurajima (Japan) and Cordón Caulle (Chile) volcanoes, agree well with our laboratory determinations on ash from the same deposits, with values of U ⁎ th ranging from 0.13 to 0.38 m/s. Our results show that the median grain size of the deposit and particle shape have a stronger control on U ⁎ th than the local substratum nature and deposit texture.

Thermal-infrared remote sensing is used to monitor and study hazardous volcanic phenomena. Thermal cameras are often used by monitoring centers and laboratories. A physical comprehension of their behavior is needed to perform quantitative measurements, which are strongly dependent on camera features and settings. This makes it possible to control the radiance measurements related to volcanic processes and, thus, to detect thermal anomalies, validate models, and extract source parameters. We review the theoretical background related to the camera behavior beside the main features affecting thermal measurements: Atmospheric transmission, object emissivity and reflectivity, camera characteristics, and external optics. We develop a Python package, PythTirCam-1.0, containing pyTirTran, a radiative transfer model based on the HITRAN database and the camera spectral response. This model is compared with the empirical algorithm implemented into a commercial camera. These two procedures are validated using a simple experiment involving pyTirConv, an algorithm developed to recover the radiometric thermal data from compressed images collected by monitoring centers. Python scripts corresponding to the described methods are provided as open-source code. This study can be applied to a wide variety of applications and, specifically, to different volcanic processes, from earth and space.

Steady-state volcanic activity implies equilibrium between the rate of magma replenishment and eruption of compositionally homogeneous magmas, lasting for tens to thousands of years in an open conduit system. The Present-day activity of Stromboli volcano (Aeolian Islands, Southern Italy) has long been recognised as typical of a steady-state volcano, with a shallow magmatic reservoir (highly porphyritic or hp-magma) continuously refilled by more mafic magma (with low phenocryst content or lp-magma) at a constant rate and accompanied by mixing, crystallisation and eruption. The lp-magma is erupted only during more violent explosive events (paroxysms), which usually occur at intervals of a few years. However, the two most recent paroxysms occurred at very short timescales on 3 July and 28 August 2019 offering the unique opportunity of obtaining crucial information on the current magma dynamics of Stromboli.Albeit the plumbing system shows such uniformity, clinopyroxene phenocrysts exhibit marked chemical heterogeneities and complex textures caused by continuous lp-hp magma mixing as well as antecryst recycling from different mush portions. The compositional zoning in clinopyroxene provides essential information on pre-eruptive magma dynamics, indicating multi-stage crystallization across the lp-hp-reservoirs, where diopsidic compositions are markers of more primitive, high-T magmas injecting into shallow, low-T domains of the plumbing system. By comparing clinopyroxene texture, chemistry and residence times from the Present-day eruptions with the previous Post-Pizzo activity, we conclude that a distinct phase in the life of Stromboli volcano commenced after the violent 2003 paroxysm. Our observations suggest there are more efficient mechanisms of mush disruption and cannibalization, in which old diopsidic antecrysts are continuously remobilized and transported by the lp-magmas permeating the mush. The disappearance of diopsidic recharge bands within augitic overgrowths indicates that over time, magmatic injections feeding the persistent Present-day activity are more intensively mixed and homogenized prior to eruption.

Stromboli Volcano was very active in the summer of 2019: Two paroxysms dramatically changed the summit craters of the volcano on July 3 and August 28. The first intense paroxysmal eruptive sequence involved both the North and the Central-South (C-S) crater areas and has generated an eruptive plume rising 4 km above the summit (924 m a.s.l.) while the incandescent material set fire to vegetation on the flanks of the volcano. Volcanic products from the laterally directed explosions and from the collapse of the external crater terrace generated two pyroclastic flows that travelled down the Sciara del Fuoco (SdF) and for several hundred of meters out to sea. Between July 3 and August 28, the activity was characterised by lava flows in the Southern sector of the SdF and by very intense Strombolian activity at a set of small scoria cones that grew around the vents, particularly in the N crater area. The second paroxysmal eruption occurred on August 28 again involving the two crater areas and producing an eruptive column that rose 4 km above the summit. Material from the eruption and from the collapse of the rim of the C-S area contributed to the generation of a pyroclastic flow that travelled down the SdF and out to sea. Important morphological variations to the crater terrace were evident after the two paroxysms.We used UAVs to monitor morpho-structural changes of the Stromboli volcano following the paroxysmal eruptions; in particular, five high-resolution UAV survey campaigns have been performed since May 2019. The aerial images were acquired using two different UAVs, a DJI Mavic 2 Pro and a Wingcopter. Using Structure-from-Motion (SfM) techniques we generated DEMs (Digital Elevation Model) and orthoimages with a resolution ranging between 0.2 and 0.5 m. An additional 1 m-resolution DEM was extracted from available tri-stereo Pleiades satellite imagery and chosen as pre-paroxysm surface. Using the orthoimages it was possible to map the distribution of eruption products and determine the morpho-structural changes. Furthermore, the topographic approach (subtraction between two different surfaces DEMs) with a cut-and-fill procedure was chosen to calculate the volume gain (in the southern sector of the SdF) and loss (in the crater areas).This work demonstrates the usefulness of the combined use of UAVs and SfM techniques to map volcanic products, to highlight morphological changes and perform volume estimations. The data collected during these field efforts and the temporal comparisons of the DEMs represent a fundamental contribution to both volcanic hazard assessment and risk mitigation, and can be used to support civil protection operations.

The resuspension of volcanic ash deposits by wind is a well-known source of hazard following explosive eruptions. Besides the mail control exerted by the local wind field, ash resuspension is also influenced by: 1) atmospheric humidity; 2) features of the deposit (grain size distribution, sedimentary structures, etc.), and 3) features of the substrate (i.e. moisture, roughness). Ash resuspension is modeled using numerical simulations, which however require physical characterization and identification of the critical parameters controlling ash resuspension. Wind tunnel studies on volcanic particles are very limited and restricted to laboratory parameterizations, with in-situ effects not been parameterized. We tested field experiments of volcanic ash resuspension developing a portable wind tunnel and deploying on proximal (3 km) ash deposits from the semi-sustained activity of Sakurajima volcano (Japan) and from distal (250 km ca.) ash deposits from the 2011 Cordon Caulle eruption (Chile). The wind tunnel is calibrated with both LDA and pitot tubes measurements. The device allows generating a controlled wind profile within a 110x12x12 cm test section, which is placed directly on an untouched test bed of naturally deposited ash. Two types of experiments were performed: 1) ramp up speed experiments, where the wind speed is increased until reaching the threshold friction speed on four different substrates; 2) constant speed experiments, where three wind speed values where kept for 20 minutes using the same substrate. The threshold friction speed is measured with a hot wire anemometer, and the movement of resuspended ash is detected by means of multiple high speed and high definition digital camcorders. In-situ measured threshold friction speeds are compared to 1) in situ observed episodes of resuspension driven by local winds and 2) laboratory determination of threshold friction speed in controlled environmental conditions, and using the same ash deposited homogeneously.

Nanoparticles (NPs) are small structures under 100 nm in dimension. Interrelationships among the morphological parameters and toxicity of NPs have been the focus of several investigations that assessed potential health risk in environmentally-exposed subjects and the realistic uses of NPs in medical practice. In the current review, we provide a summary of the cellular mechanisms of membrane-mediated transport, including old and novel molecules that transport nanostructures across cellular membranes. The effects of geochemical exposure to natural NPs are evaluated through epidemiological data and cancerous pathways activated by Fe2+ NPs. Specifically, we discuss screening for papillary thyroid carcinomas in the inhabitants of the Sicilian volcanic area surrounding Mount Etna to compare the incidence of thyroid carcinoma in this population. Lastly, considering the increased production of carbon nanotubes (CNTs), we examine the toxicity and potential use of these engineered NPs in drug delivery of an extensive amount of therapeutic and imaging molecules (theranosis) that can be conjugated to CNTs.

We present a detailed physical and geochemical analysis of a small-scale eruption at the type basaltic volcano, Mount Etna, Italy, that spanned 9 days in May 2016. A complexity rarely seen within the short timeframe was present with the style of activity manifesting as outgassing, strombolian explosions to weak fountaining, and lava flows, while the eruption migrated between most of the summit craters. Through microprobe analysis of phenocrysts, groundmass glasses and melt inclusions we define geochemical trends by differentiating the eruptive products into two groups – the explosive tephra produced by lava fountaining, and lava and scoria emitted during Strombolian explosions. We highlight plagioclase and olivine compositions and variations in glass compositions as evidence for the eruption of multiple magma bodies. The eruptive sequence was triggered and fed by a batch of magma reaching the surface after limited degassing and crystallisation. Despite its small mass (about 0.01% of the total erupted magma), it generated three lava fountains occurring within a four-day timespan, producing ash-rich plumes which reached heights of a few km above the vent. The same batch destabilised a much larger mass (the remaining 99.99%) of crystal-richer magma stored at shallow depth that then erupted as lava from the same vent system in temporal continuity with the initial batch. The eruption was concluded by minor spattering and final Strombolian activity. The compositions of the magma batches suggest that the shallow magma reservoir likely exists as a network of interconnected dykes, probably fed by the same that partly erupted in the years/months preceding the May 2016 eruption. Variation in explosivity of the eruption was directly controlled by pre-eruptive degassing histories of each magma batch.