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The number of explosive eruptions at Shiveluch Volcano has significantly increased over the past years, which requires close volcanic monitoring using all available techniques. In order to implement a new monitoring technique into integrated methods of volcano monitoring, the authors analyze response to the intensity of the vertical component in the atmospheric electrical field (EZ AEF) during the movement of ash clouds. Two eruptions of different intensity that occurred December 16, 2016 and June 14, 2017 at Shiveluch were selected for study. We used a combination of satellite, seismic, and infrasound data to select signals in the EZ AEF field. Signals with negative polarity that accompanied ashfalls in the EZ AEF dynamics were registered for both eruptions within the closest area (< 50 km). In the former case, the ash cloud was “dry” and thus it caused aerial-electrical structure of the negatively charged cloud. In the latter case, a strong explosion sent into the atmosphere the large volume of ash and volcanic gases (98% in form of vapour) that resulted in the formation of a dipolar aerial-electrical structure caused by eolian differentiation within the closest area. At the distance of more than 100 km we registered a positive-going signal that is attributive to the aerial-electrical structure of the positively charged type of the cloud.

It is shown that the rate of explosive eruptions on Shiveluch Volcano has become increasingly high during recent years, which makes the monitoring of the volcano using all available means highly urgent. We seek to introduce another technique into the multidisciplinary monitoring of explosive eruptions by analyzing responses in the vertical component of the atmospheric electric field (EZ AEF) during the passage of eruptive plumes. We considered two Shiveluch eruptions that were different in vigor that occurred on December 16, 2016 and on June 14, 2017.The signals in the EZ AEF were selected using multidisciplinary observations, viz., satellite-based observations, seismic, and infrared observations. Signals of negative polarity were recorded in the EZ AEF dynamics in the near zone ( 100 km), the explosion produced a signal of positive polarity coming from an aero-electrical structure of the “positively charged plume” type from the aerosol column.

Large explosive eruptions of volcanoes pose the highest hazard to modern jet f lights, because such eruptions can eject as much as several cubic kilometers of volcanic ash and aerosol into the atmosphere during a few hours or days. The year 2016 saw eruptions on 5 of the 30 active Kamchatka volcanoes (Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, and Zhupanovsky) and on 3 of the 6 active volcanoes that exist on the North Kuril Islands (Alaid, Ebeko, and Chikurachki). Effusive activity was observed on Sheveluch, Klyuchevskoy, Bezymianny, and Alaid. All volcanoes showed explosive activity. The large explosive events mostly occurred from September through December (Sheveluch), a moderate ash emission accompanied the entire Klyuchevskoy eruption in March–November, and explosive activity of Karymsky, Zhupanovsky, Alaid, and Chikurachki was mostly observed in the earlie r half of the year. The ash ejected in 2016 covered a total area of 600 000 km2, with 460 000 km2 of this being due to Kamchatka volcanoes and 140 000 km2 to the eruptions of the North Kuril volcanoes. The activity of Sheveluch, Klyuchevskoy, and Zhupanovsky was dangerous to international and local f lights, because the explosions sent ash to heights of 10–12 km above sea level, while the eruptions of Bezymianny, Karymsky, Alaid, Ebeko, and Chikurachki were dangerous for local flights, since the ash did not rise higher than 5 km above sea level.

Ilopango caldera erupted episodically at least 13 tuff-forming eruptions with a minimum estimate volume of 1–5 km 3 DRE per eruption, reaching up to 150 km 3 DRE for the first caldera-forming eruption. All tuffs are of dacitic-rhyolitic composition. The complete pyroclastic sequence spans a range in time from 1.785 to 0.0015 Ma, and based on stratigraphy and geochronology constraints can be divided into three formations: the Comalapa, Altavista and Tierras Blancas formations. In this work, we focus on the members of the newly described Altavista Formation (middle part of Ilopango caldera volcanic sequence), which consist of six consolidated pyroclastic deposits or tuffs. Each tuff corresponds to a specific eruption followed by a period of quiescence during which soil beds were developed on the deposits. The ages of the Altavista Formation ranges from 918 to 257 ka, based on new 40 Ar/ 39 Ar, U/Pb-zircon, and U/Th-zircon analyses. The tuffs of this formation show similar characteristics in mineralogy and composition. They are calcalkaline, rhyodacitic tuffs, with plagioclase, clinopyroxene, and hornblende. From field mapping and descriptions of the deposits, we have inferred the eruptive styles that include pumice fallouts, pyroclastic density currents and also hydromagmatic explosions. The common vent in all tuffs was the Ilopango caldera and each member of the Altavista Formation could correspond to a caldera collapse event, except for one of the six eruptions. The volume of each member was estimated to be >30 km 3 DRE, which is the same order of magnitude than that estimated for the Tierra Blanca Joven (TBJ) eruption at about 1,500 B. P, and smaller than those of the ignimbrites of the Comalapa Formation, the first three members of the Ilopango caldera reported previously. The tuffs of the Altavista Formation are visible up to 15–20 km away from the caldera's topographic margin. The recurrence interval of large explosive events at the Ilopango caldera was established by integrating the stratigraphic and geochronologic data of all 13 ignimbrites and pumice fallouts erupted from Ilopango caldera since the first one at 1.78 Ma to the last explosive event (TBJ). © 2019 Elsevier B.V., This study was financed by CONACYT-CB grant 240447 to GJAD. We appreciate the logistical support of the Ministerio de Medio Ambiente y Recursos Naturales – MARN, and of the Policia Nacional Civil – PNC, of El Salvador. We thank the doctoral scholarship grant to the first author from CONACYT-Mexico.

Magma responds to applied stresses in either a viscous or elastic manner, depending on the time scales over which strain is accommodated. For silicic magmas, high strain rates of explosive volcanism cause brittle fragmentation and produce abundant small particles (ash). The A.D. 2012 Havre (Kermadec arc, southwestern Pacific Ocean) eruption at ∼900 m water depth deposited a unit of silicic ash with features indicative of syn- and/or post-fragmentation viscous deformation. Viscously deformed ash makes up 3%-35% of the two main ash subunits, S1 and S2, with the remaining ash formed by brittle fragmentation. Viscous behavior of melt during production of fine ash is unexpected for the silicic Havre magma, and for the high strain rates typical of fine fragmentation. The occurrence together of viscous and brittle ash grains suggests local and/or short-term variations in eruption conditions. We infer an explosive eruption mechanism modified by magma-water interaction, during which multi-source steam-veiled fragmentation sites permitted rapid viscous deformation of ash prior to contact with water.

In this work, we search for physical and chemical climatological anomalies preceding major volcanic explosive eruptions (mostly VEI—Volcanic Explosivity Index 4+) occurred from 2002 to 2017, by applying two specific algorithms, i.e. CAPRI and MEANS. The former algorithm has been already used for a multi-climatological analysis of the Amatrice-Norcia 2016–2017 earthquake preparatory phase (Piscini et al., In: Pure Appl Geophys, 174:3673–3688, 2017). Here we analyse some climatological parameters for a three-month period before each volcanic explosive eruption then we compare the behavior with the typical one of the past. The analysis is applied to an area with dimensions comparable to the volcano crater, because it is the increase of the magmatic camera activity that, in turn, can cause a temperature increase whose evidence could be detected at the surface (Slezin, In: J Volcanol Geotherm Res, 122(1–2), 7–50, 2003), while the use of a larger area would provide a greater probability of occurrence of other events (e.g., other volcano eruption, meteorological storms, etcetera). Therefore, a smaller area of study reduces the risk to get “false alarms”. In particular, we considered thermal skin temperature, (skt) and total water vapour content (tcwv) from ECMWF European centre and aerosol optical thickness (AOT), sulphur dioxide (SO2) and atmospheric dimethylsulphide (DMS) are obtained from NASA MERRA-2 Global Modeling and Assimilation data archive. The latter compound was added in the analysis to check the validity of the method, since we did not expect significant anomalies from this parameter. The models above described are used for their temporal-spatial completeness, allowing performing time series analyses and for a real time monitoring on a global scale. By simultaneous analysis, we found for almost all volcanic eruptions some anomalies in about all analyzed parameters that precede by 75 days to 20 days the explosion. These anomalies are not always simultaneous, but we find an interesting synchronicity that probably reveals a correlation among the different datasets. In addition, the Agung volcano, which has recently started an eruptive activity (25 November 2017) without reaching a VEI4+ explosion, has also been investigated. The data related to this volcano present a small number of anomalies, much lower than all attributed to the other analyzed explosive volcanoes and this is in high agreement with the low-explosive nature of the Agung volcano eruption. We find that the occurrence of thermal anomalies typically preceding stratovolcano/caldera eruptions seems to take place some days after SO2 emissions. The climatological anomalies that precede eruptions at high latitudes usually surround the volcano in a wider area outside the volcanic edifice. We verify that the number of positive anomalies is systematically greater in the year that precedes the investigated eruption with respect to a quiet year of comparison with accuracy from 91 to 100%, suggesting that the applied methods detected climatological anomalies likely related to imminent volcanic eruptions.

Mt. Etna, in Sicily (Italy), produces effusive and explosive eruptions from summit craters and flanks. Petrology of erupted products has proved fundamental to explore the relationship between magma dynamics within the plumbing system and eruptive styles. Data of Sr Nd isotopes are quite scarce if compared with the great number of chemical analyses carried out in products of last decades. We measure Sr Nd isotopes, major and trace elements in products emitted from 2001 to 2012, and consider also published analyses of the 1995–2001 eruptions, because carried out in the same laboratories of 2001–2012 ones. Furthermore, we take into account other published analyses extending back to the 14th century, even if performed by different facilities. Based on this dataset, magma dynamics operating at different timescales inside the volcano's plumbing system have been explored. Our analyses evidence that, from 2001–2012, three magma types are present in the volcano's plumbing system: (i) a deep and poorly evolved basaltic and K-trachybasaltic magma, enriched in radiogenic Sr and LILE, erupted during the 2001 and 2002–03 flank activity; (ii) a shallower more evolved K-trachybasaltic magma, less enriched in radiogenic Sr, feeding both summit and flank eruptions and (iii) an uncommon, and scarcely radiogenic hawaiitic magma, LILE poor, emitted exclusively from a small sector of the 2002–03 eruptive fissures. By considering a broader time scale, from 14th to 21st century, we conclude that: (i) different magmatic components are present in the deep volcano's plumbing system, at about 10–12 km b.s.l; (ii) a decoupling of geochemical and isotopic features in magmas stored at different depths is observed after the 1974 flank eruption up to date; (iii) mixing between different magmas is an efficient magmatic process to produce magma differentiation at Mt. Etna, regardless of the investigated temporal scale.

High-current impulse experiments were performed on volcanic ash samples to determine the magnetic effects that may result from the occurrence of volcanic lightning during explosive eruptions. Pseudo-ash was manufactured through milling and sieving of eruptive deposits with different bulk compositions and mineral contents. By comparing pre- and post-experimental samples, it was found that the saturation (i.e., maximum possible) magnetization increased, and coercivity (i.e., ability to withstand demagnetization) decreased. The increase in saturation magnetization was greater for compositionally evolved samples compared to more primitive samples subjected to equivalent currents. Changes in remanent (i.e., residual) magnetization do not correlate with composition, and show wide variability. Variations in magnetic properties were generally more significant when samples were subjected to higher peak currents as higher currents affect a greater proportion of the subjected sample. The electrons introduced by the current impulse cause reduction and devolatilization of the ash grains, changing their structural, mineralogical, and magnetic properties.

Historic eruptions of Earth's only active carbonatite volcano, Oldoinyo Lengai (Tanzania), have repeatedly switched from low energy carbonatite lava extrusion to highly energetic explosive silicate volcanism, most recently in 1966–67 and 2007–08. The explosive eruptions produce strongly Si-undersaturated peralkaline silicate ashes with unusually high (Na + K)/Al of 3.4–6.3 when compared to the average peralkalinity of ∼0.8 in the East African Rift System. A series of experiments in the carbonatite–clinopyroxene system at 750–1150 °C, 0.1 GPa, reveal that augitic clinopyroxene breaks down peritectically at >900 °C yielding strongly peralkaline conjugated silicate- and carbonatite melts. The clinopyroxene-derived silicate melt dissolves (Na,K)_2O from the (Na,K)_2CO_3-component of the carbonatite leading to high peralkalinities and to liberation of excess CO_2, since the solubility of carbon dioxide in silicate liquids is ≪1 wt.% at subvolcanic pressures. Carbonatite injection into subvolcanic clinopyroxene-rich crystal mushes hence explains the occurrence of strongly peralkaline silicate melts and provides a mechanism for CO_2-driven explosive eruptions. The silicate melt compositions mostly depend on the (Na + K)/Ca ratio of the intruding carbonatite, the silicate ashes erupted in 1966–67 and 2007–08 require an interaction of a clinopyroxene-rich crystal mush with a slightly less evolved alkali-carbonatite than presently erupted at Oldoinyo Lengai. The mechanism identified here, where mineral breakdown induced melt hybridization triggers volatile saturation and highly explosive volcanism is generally applicable to igneous systems that involve carbonatites or other low-viscosity CO_2-bearing alkaline silicate melts.

Ciomadul is the youngest volcanic system in the Carpathian-Pannonian Region recording eruptive activity from ca. 1 Ma to 30 ka. Based on combined zircon U-Th and (U-Th)/He geochronology, Ciomadul volcanism is divided into two main eruptive periods: Old Ciomadul (1 Ma – 300 ka; OCEP) and Young Ciomadul Eruptive Period (160–30 ka; YCEP). OCEP activity comprises Eruptive Epochs 1–3, whereas new ages for eight lava domes and four pyroclastic units belonging to the YCEP lead to its further subdivision into two eruptive epochs: Eruptive Epochs 4 and 5. The extrusion of most of the lava domes occurred between 160 and 90 ka (Eruptive Epoch 4) during three eruptive episodes at ca. 155 ka, 135 ka and 95 ka (Eruptive Episodes 4/1, 4/2 and 4/3, respectively) along a NE-SW lineament, which is perpendicular to the regional NW-SE trend of the Calimani-Gurghiu-Harghita volcanic chain. Eruptive Epoch 5 occurred after a ca. 40 kyr of quiescence at ca. 55–30 ka, and is mainly characterized by explosive eruptions with a minor lava dome building activity. All of the dated pyroclastic outcrops, together with the lava dome of Piscul Pietros, belong to the older Eruptive Episode 5/1, with an eruption age of 55–45 ka. The eruption centers of Eruptive Epoch 5 are located at the junction of the conjugated NW-SE and NE-SW lineaments defined by the older eruptive centers. The whole-rock geochemistry of all studied samples is fairly homogeneous (SiO2 = 63–69 wt%, K2O = 3–4 wt%). It also overlaps with the composition of the lava domes of the Old Ciomadul Eruptive Period, implying a monotonous geochemical characteristic for the past 1 Myr. The eruption rates for the Ciomadul volcanism were determined based on the erupted lava dome volume calculations, supplemented with the eruption ages. The activity peaked during the Eruptive Epoch 4 (160–90 ka), having an eruption rate of 0.1 km3/kyr. In comparison, these values are 0.05 km3/kyr for the YCEP (160–30 ka) and 0.01 km3/kyr for the overall Ciomadul volcanism (1 Ma–30 ka). Based on the geochemical characteristics, the quiescence periods and the lifetime of the complex, as well as the relatively small amount of erupted material, this volcanic system can be placed in a subduction-related post-collisional geodynamic setting, which shows strong chemical similarities to continental arc volcanism. The commonly found long repose times between the active phases suggest that the nature of a volcano cannot be understood solely based on the elapsed time since the last eruption. Instead, comprehensive geochronology, coupled with the understanding of the magma storage behavior could be a base of hazard assessment for volcanic fields, where the last eruptions occurred several 10's of thousand years ago and therefore they are not considered as potentially active.

The Dawn spacecraft has imaged several putative cryovolcanic features on Ceres, and several lines of evidence point to past cryovolcanic activity at Occator crater. It is therefore possible that cryovolcanism played a key role in delivering sodium carbonate- and chloride-enriched brines to Ceres’ surface in recent geological times. The detection of a 200 km×200 km negative Bouguer anomaly beneath Occator suggests the presence of a low-density region beneath the crater. If this region is a residual, partially crystallized, cryomagma chamber, excess pressures caused by its gradual freezing, or stresses produced by the Occator-forming impact, could have facilitated the delivery of cryolavas to the surface in the geologically recent past. Here, the progressive solidification of a cryomagma chamber beneath Occator and implications for the delivery of cryolavas to the surface has been explored. Models for the behavior of cryolavas at Ceres’ surface, and for the formation of the Cerealia Dome and Vinalia Faculae, are also presented. Minimal crystallization of a subsurface fluid reservoir located at the crust-mantle boundary could have driven cryolavas enriched in chloride salts and NH3 to Ceres’ surface. However, cryolavas enriched in sodium carbonates would have had to have existed at shallower levels in the crust in order to be delivered to the surface via pressure-driven ascent. Depending on the size of the reservoir, cryolavas could have been driven to Ceres’ surface for tens to hundreds of millions of years after cooling of the cryomagma chamber commenced. The mineralogy at Occator is suggestive of subsurface cryomagma reservoirs enriched in sodium carbonate and chloride salts. Aqueous solutions enriched in chloride salts and/or ammonia would have arrived at the surface at warm enough temperatures to erupt if transported in propagating fractures that traveled at least 10−5 m/s. Additionally, if the Cerealia Dome was formed from viscous cryolava extrusions, bulk kinematic lava viscosities may have been between 106–108 m2/s at the onset of relaxation. Plausible relaxation times to form the dome, which are linked to bulk cryolava rheology, are found to have ranged from 2.5 to 273 days. Moreover, the low volatile content necessary to drive explosive eruptions on Ceres supports the possibility that Cerealia and Vinalia Faculae were emplaced as a consequence of ballistic eruptions. The enigmatic geology of Occator crater is consistent with a diversity of exchange processes operating on Ceres in the geologically recent past. Further, the processes that have occurred at Occator could shed light on the changing geology associated with a relic ocean world. Future studies of Occator and Ceres should be undertaken with these results in mind.

Two correlated tephra deposits, each 13 cm thick in the Aisen region of southern Chile, one in a lacustrine sediment core from the Mallin el Toqui (MET) peat bog and another from a subaerial soil exposure ∼10 km to the west in the Rio Maniguales (RM) valley, preserve evidence for a large explosive eruption of Mentolat volcano, one of the five stratovolcanoes of the southernmost portion of the Andean Southern Volcanic Zone (SVZ). This eruption is constrained in age to ≥11,728 cal years BP by radiocarbon dating of organic matter from the MET sediment core and is termed the ∼11.7 ka MEN event. The two tephra deposits are identical and based on their petrology, bulk tephra, glass, and amphibole geochemical characteristics, are attributed to an eruption of Mentolat volcano. Both contain pumice lapilli with glass compositions that ranges from 59 to 76 wt. % SiO2, with medium to low-K2O calc-alkaline composition and trace element abundances similar to both lavas and other tephras derived from Mentolat. They have abundant amphibole, plagioclase, orthopyroxene, and clinopyroxene phenocrysts, with a smaller proportion of olivine and Fe-Ti oxides, and a minor amount of distinctive crustal xenoliths with both unfoliated and foliated textures. Amphiboles have low K2O (0.20–0.37 wt. %) and TiO2 (1.5–3.8 wt. %) and are similar geochemically to amphiboles from other Mentolat-derived tephra (K2O = 0.14–0.43 wt. % and TiO2 = 1.9–2.4 wt. %), but distinct from amphiboles in lavas and tephra derived from other volcanoes in the southernmost SSVZ including Cay (K2O = 0.47–0.55 wt. % and TiO2 = 2.4–3.1 wt. %) and Melimoyu (K2O = 0.39–0.52 wt. % and TiO2 = 2.8–4.5 wt. %). Amphiboles from the ∼11.7 ka MEN tephra formed over a broad range of pressures (154–406 MPa), temperatures (834-969 °C), and magma water contents (4.9–7.0 wt. %), which overlap with the physical-chemical conditions for the formation of amphiboles from other Mentolat-derived tephra. The two correlated tephra deposits, which are located ∼95 km southeast of Mentolat, are correlative with tephra of similar age identified in 12 other lacustrine sediment cores from the region, for which, based on their petrology and the geochemistry of their tephra glass and amphiboles, Mentolat is also the likely source volcano. This eruption produced approximately 1.8 km3 of bulk material with an estimated magnitude of 5.2. Mentolat has produced numerous (>18) explosive eruptions since glacial retreat from the region and future explosive eruptions from this center could potentially impact local population centers and the agricultural industry in southern Chile and Argentina.

The Showa crater of Sakurajima, an andesitic volcano in Japan, resumed eruptive activity in June 2006 for the first time in 58 years. Explosive eruptions at the Showa crater have been active since 2009. Micro-earthquake swarms have sometimes been observed in the 1 or 2 h preceding these eruptions since 2012 and have frequently occurred during periods of low eruptive activity. These precursory micro-earthquakes are dominated by high-frequency (5–6 Hz) components and no clear S-wave and are thus classified as BH-type earthquake swarms. The hypocenters of the earthquakes are located in a shallow region (depth of approximately 1 km) near the Showa crater. Prior to the eruptions, the onset of inflation has been observed by extensometers, followed by precursory earthquake swarms 30 min to 1 h later. In the case of insufficient ground contraction, the precursory earthquakes reoccur when the strain reaches the same level it showed just before the eruptions occurred. From the occurrence period and pattern of the precursory earthquakes, it appears they may be generated within a narrow conduit leading to the Showa crater.

The Ilopango caldera is located in the central part of El Salvador, within the right-lateral El Salvador Fault System (ESFZ) and adjacent to the capital city of San Salvador. The caldera has a polygonal shape of 17 × 13 km and hosts an intra-caldera lake. Ilopango caldera had multiple collapse eruptions that formed widespread and voluminous silicic ignimbrites. Volcanic activity of the caldera has been controlled by strike-slip faults of the ESFZ. In this work we present the geological characteristics of the first three ignimbrite-forming eruptions of Ilopango caldera, providing an interpretation of the origin and initial stages of the volcanic evolution of this caldera complex. An initial extensional regime of the ESFZ possibly developed a graben at or near the actual Ilopango caldera, where the graben's master faults worked as fissure vents during the first caldera collapse. The Olocuilta Ignimbrite was emplaced at 1.785 ± 0.01 Ma BP, with a Dense Rock Equivalent (DRE) volume > 50 km3 (probably ~300 km3). The ESFZ stress gradually changed from extensive to transtensive, inducing the second collapse associated with a pull-apart caldera, producing the Colima Ignimbrite at 1.56 ± 0.01 Ma BP, with a DRE volume of >11 km3. The transtensive regime increased along the ESFZ, producing the third collapse in the pull-apart graben caldera apparently affected by the newly formed strike-slip San Vicente Fault. This phase corresponds to the explosive eruption that formed the Apopa Ignimbrite at ~1.34 Ma BP, with >9 km3 DRE volume. The latter ignimbrite marks a change in the eruptive style producing hydromagmatic pyroclastic flows followed by a dense ignimbrite with coignimbrite lithic breccias. These features suggest the involvement of water that could come from a paleoIlopango lake within the caldera depression associated with the second caldera collapse at 1.56 Ma BP. Ilopango is thus a multistage caldera system associated with the largest explosive events registered in El Salvador so far., This study was financed by CONACYT-CB grant 240447 to GAD. We appreciate the logistical support of the Ministerio de Medio Ambiente y Recursos Naturales – MARN, and of the Policia Nacional Civil – PNC, of El Salvador. We thank the doctoral scholarship grant to the first author from CONACYT-Mexico.

Vigorous explosive eruptions that produce continuous high eruption plumes (Plinian eruptions) are generally assumed to tap a magma reservoir. The 1914 Plinian eruption at the Sakurajima volcano located on the Aira caldera rim is one such case, where the main magma reservoir was assumed to be located approximately 10 km beneath the caldera. However, we report that estimated magma storage depths immediately prior to the eruption were much shallower (0.9–3.2 km) on the basis of pressure at which volatiles within the phenocryst melt inclusions and plagioclase rims were finally equilibrated. The same is observed for two historic Plinian eruptions in 1471 and 1779. This depth is even shallower than the shallowest magma reservoir estimated from the pressure source for geodetic deformation during recent Vulcanian explosions (4 km beneath the crater). We propose that the magmas were fed from a thick conduit pre-charged from deeper reservoirs. The ground subsidence observed after 1914 within the Aira caldera may have been caused by conduit recharge following the eruption. Voluminous conduit recharge could be key to forecasting the next possible large eruption at the Sakurajima volcano.

Re-examination of central Mediterranean paleoclimate archives on tephra layers indicates that three widely dispersed tephra layers occurred during the Bronze Age, namely Agnano Mt Spina from Campi Flegrei (ca. 4.4 cal ka BP), Avellino from Somma-Vesuvius (ca. 3.9 cal ka BP), and FL from Etna (ca. 3.3 cal ka BP). Stratigraphical correlations of selected archives using these tephra layers indicate that some records have severe chronological biases, posing important limitations to the use of these archives for defining the paleoclimate conditions during the Bronze Age. Regardless of the temporal mismatches, the Agnano Mt Spina tephra layer seems to have occurred at the beginning of a centennial scale period of climatic deterioration, while the Avellino tephra layer, taking place during a wetter period, seems to mark the end of this event. The dry event bounded by the two tephra layers seems to be correlated with the so-called “4.2 event”. Instead, the FL tephra from Etna seems to herald a new climatic deterioration at ca. 3.3–3.2 cal ka BP. Although the general frame is still incomplete, these three tephra layers appear to play a fundamental role in synchronizing archives, and can lead to the definition of a detailed paleoclimatic framework of the Bronze Age in the central Mediterranean area.

We review our understanding of the exsolved volatile phase co-existing with magmas during pre-eruptive storage at the pressures and temperatures corresponding to crustal magma reservoirs. We explore the consequences and implications of such a volatile phase for magma and ore body petrogenesis and the fluid dynamics of magma reservoirs. We outline the geochemical constraints on the size and composition of the exsolved volatile phase that may co-exist with magmas in the crust. We distinguish between decompression-driven and crystallization-driven exsolution, and describe the implications of the volatiles for the dynamics of the magma reservoir, using key natural examples and case studies. We discuss eruptions triggered by second boiling, and the various regimes of magma mixing and magma overturn that may be induced by second boiling in a layered reservoir. We also explore the control of the volatile content of the magma on the mass erupted during an eruption episode, and compare our models to eruption datasets. We then turn to the mechanisms for magma-volatile separation, noting that in crystal-poor melts convective separation of exsolved volatiles may dominate while in crystal-rich melts, volatiles may generate channels or permeable-flow pathways through the crystal mush, thereby separating from the parent magma. We discuss the implications of the accumulation of the exsolved volatile phase at the roof zones of crystal-rich reservoirs for the large gas emissions observed during explosive eruptions, and for the development of metal-rich porphyry deposits.

In this paper we present new data on weathering and soil formation processes affecting alkaline pillow basalts on the summit of Mt. Cerviero (Calabria, southern Italy). We investigated two representative soil profiles using an integrated approach, including pedological, petrographic, mineralogical and geochemical investigations. We distinguished the main features inherited from the hydrothermal alteration of the pillow basalts in a submarine environment from the chemical weathering processes under meteoric conditions. Irregular geochemical patterns and chemical index of alteration values across the soil profiles indicate a lithological discontinuity between the bedrock and the upper soil horizons, as a response to soil rejuvenation, in turn controlled by erosive processes and an allochthonous pyroclastic input. The soil profiles display poor horizonation and an incipient to intermediate degree of weathering, in line with the clay mineralogy (chlorite or hydroxy-interlayered vermiculite, illite, kaolinite and varying mixed-layers). The degeneration microtextures of clay and iron-manganese coatings in one soil profile suggest their relict genesis, with an emplacement under warm-humid conditions during the last interglacial. A Late Pleistocene to Holocene age of soil development is supported by the trachytic composition of volcanic micropumices, correlated to explosive eruptions from the Campania Province or the Aeolian Islands, in both soil profiles. Geochemical indices obtained from selective extractions of pedogenetic Al, Fe and Si pools point to poor andic properties with humus-Al-complexes prevailing over short-range order minerals. Nonetheless, the latter are consistent with the presence of volcanic glass, an optically isotropic pedogenic matrix and the Andosol-like field features of the soil profiles, even if they developed in a non-volcanic area. This should lead to a partial reassessment of the volcanic versus non-volcanic origin of certain Andosols worldwide and claims a good field work as a basis for choosing the best-suited laboratory methods to fill the gap between ordinary lab and field results.

In the central Oregon Cascades, mafic volcanic edifices include both short-lived cinder cones and a spectrum of much larger, longer-lived volcanoes. We analyzed olivine-hosted melt inclusions from explosive eruptions from three of the larger edifices to compare crystallization, volatile contents, and storage depths to those of the shorter-lived cinder cones. The melt inclusions were sampled from calc-alkaline basalt to basaltic andesite tephra collected from Belknap, Mount Washington, and North Sister volcanoes. Olivine host compositions are Fo80–83, Fo79–82, and Fo74–81, respectively. These Fo values are lower than the published values for nearby cinder cones (mostly Fo83–85), indicating greater extents of differentiation beneath the longer-lived edifices. The H2O contents of melt inclusions from each of the three volcanoes form a continuous range of values from ≤0.5 to ~2.5 wt% H2O. Many of the inclusions contain a vapor bubble, and the bubbles are mostly in the range of 1.0–6 vol% of the inclusion. After correcting bubble-bearing inclusions for the amounts of CO2 lost to the bubbles, our data show that variable degassing and olivine crystallization occurred beneath the larger edifices over a wide range of depths from > 7 km (> 2–5 kbar) to as shallow as ~0.1 km (~10–30 bars). In contrast, olivine-hosted melt inclusions from nearby cinder cones record entrapment at > 4–5 km depth, with no evidence for shallow crystallization and storage (e.g. Ruscitto et al., 2010 ). Our results demonstrate that the longer-lived edifices develop a vertically extensive zone of storage and crystallization that extends from the middle to the upper crust and continues into the core of the edifice itself. Modeled primary magma compositions for Belknap, Mount Washington, and North Sister are similar to those from nearby cinder cones, indicating that shield volcanoes and nearby cinder cones are supplied by the same magma sources. The results demonstrate that the shield volcanoes have more complex, shallow magmatic plumbing systems than that of the cinder cones.

Multi-sensor strategies are key to the real-time determination of Eruptive Source Parameters (ESPs) of explosive eruptions necessary to forecast tephra dispersal and deposition accurately. In order to explore the capacity of these strategies in various eruptive conditions, we analyze data acquired by two Doppler radars, ground- and satellite-based infrared sensors, one infrasound array, visible video-monitoring cameras as well as data from tephra-fallout deposits associated with a weak and a strong paroxysmal event at Mount Etna (Italy). We find that the different sensors provide complementary observations that should be critically analyzed and combined to provide comprehensive estimates of ESPs. First, all measurements of plume height agree during the strong paroxysmal activity considered, whereas larger discrepancies are found for the weak paroxysm due to rapid plume and cloud dilution. Second, the event duration, key to convert the Total Erupted Mass (TEM) in Mass Eruption Rate (MER) and vice versa, varies depending on the sensor used, providing information on different phases of the paroxysm (i.e. lava fountain, lava fountain-fed tephra plume, waning phase associated with plume and cloud expansion in the atmosphere). Third, the derived average TEM agrees among all sensors for both weak and strong paroxysms. Finally, given that unfortunately no existing strategy or combination of strategies can provide information on the Total Grain-Size Distributions in real time, a combination of grainsize data from both tephra-fallout deposits and satellite retrievals is recommended to provide an accurate description of past eruptions to be used as a proxy for real-team tephra dispersal forecasting.

Shallow high-silica granites provide a window into processes that may precede many styles of rhyolitic volcanic eruptions., Rhyolitic melt that fuels explosive eruptions often originates in the upper crust via extraction from crystal-rich sources, implying an evolutionary link between volcanism and residual plutonism. However, the time scales over which these systems evolve are mainly understood through erupted deposits, limiting confirmation of this connection. Exhumed plutons that preserve a record of high-silica melt segregation provide a critical subvolcanic perspective on rhyolite generation, permitting comparison between time scales of long-term assembly and transient melt extraction events. Here, U-Pb zircon petrochronology and 40Ar/39Ar thermochronology constrain silicic melt segregation and residual cumulate formation in a ~7 to 6 Ma, shallow (3 to 7 km depth) Andean pluton. Thermo-petrological simulations linked to a zircon saturation model map spatiotemporal melt flux distributions. Our findings suggest that ~50 km3 of rhyolitic melt was extracted in ~130 ka, transient pluton assembly that indicates the thermal viability of advanced magma differentiation in the upper crust.

Kolumbo is the largest of twenty submarine volcanic cones, tectonically aligned in the transtentional Anydros basin, one of the most seismically active zones in the South Aegean Volcanic Arc, whose magmatism is related to the subduction of the African Plate beneath the Aegean microplate. Kolumbo explosively erupted in 1650 CE, causing the death of 70 people on Santorini, which is only 7 km SW of Kolumbo. Explorative cruises employing ROVs discovered a high temperature (220°C) hydrothermal field with CO2-rich discharges and accumulation of acidic water at the bottom of the crater (505 m b.s.l.), increasing the related hazard. A possible magma chamber was recognized below the crater at depth 9-6 km by seismic data [Dimitriadis et al. 2009]. Geochemical data [Klaver et al. 2016] suggest that Kolumbo have a different mantle source and storage system from Santorini. It is fundamental to understand the behaviour of this volcano, and how its storage and plumbing system works, to correctly assess risk for nearby islands.We present petrographic, geochemical and isotopic data of samples collected during the cruises and by divers. Most samples represent the juvenile products of the 1650 CE activity, characterizing different magmas interacting before the eruption. They consist of white rhyolitic pumices with grey and black bands, also including basaltic-andesitic enclaves. Plagioclase, biotite, pyroxenes are the main mineral phases; olivine is found in the mafic enclaves. Minerals show quite complex zoning and a large compositional variability. Fresh lithic lavas were sampled; they also have amphibole and can be subdivided in three groups with distinctive petrographic textures that are well reflected in their different chemical compositions. They give information on the early history of the volcano and on how the rhyolitic magma could have been generated.Our data suggest the presence of a complex storage system where the most evolved magma differentiated by assimilation and fractional crystallization, undergoing several inputs of mafic magmas. Early batches of new melts initially mixed with the resident ones, whereas later arrivals only mingled with the rhyolitic magma, thus possibly representing the final trigger of the eruption.

Large explosive volcanic eruptions inject sulphur into the stratosphere where it is converted to sulphur dioxide and sulphate aerosols. Due to atmospheric circulation patterns, aerosols from high-latitude eruptions typically remain concentrated in the hemisphere in which they are injected. Eruptions in the high-latitude Northern Hemisphere could thus lead to a stronger hemispheric radiative forcing and surface climate response than tropical eruptions, a claim that is supported by a previous study based on proxy records and the coupled aerosol-general circulation model MAECHAM5-HAM. Additionally, the subsequent surface deposition of volcanic sulphate is potentially harmful to humans and ecosystems, and an improved understanding of the deposition over polar ice sheets can contribute to better reconstructions of historical volcanic forcing. On this basis, we model Icelandic explosive eruptions in a pre-industrial atmosphere, taking both volcanic sulphur and halogen loading into account. We use the fully coupled Earth system model CESM2 with the atmospheric component WACCM6, which extends to the lower thermosphere and has prognostic stratospheric aerosols and full chemistry. In order to study the volcanic impacts on the atmosphere, environment, and sulphate deposition, we vary eruption parameters such as sulphur and halogen loading, and injection altitude and season. The modelled volcanic sulphate deposition is compared to the deposition in ice cores following comparable historical eruptions. Furthermore, we evaluate the potential environmental impacts of sulphate deposition. To study inter-model differences, we also compare the CESM2-WACCM6 simulations to similar Icelandic eruption experiments simulated with MAECHAM5-HAM.

Deception Island is amongst the most active volcanoes in the Southern Ocean, with over 20 explosive eruptions in the last ca. 200 years. The eruption that formed the caldera at Deception Island occurred 3980 ± 125 calendar years Before Present, and it is the largest eruptive event documented in Antarctica during Holocene. Since then, post-caldera volcanic activity has comprised many scattered eruptive vents across the island. Mortality of benthic organisms has been reported during the most recent eruptions occurred on the island, in 1967, 1969, and 1970 Common Era (CE), with very low abundances of organisms during the 1967–1973 CE period. Within the sea-flooded part of the caldera depression, named Port Foster, a submarine volcanic axis with several volcanic cones is observed. An interdisciplinary team sampled the best morphologically preserved volcanic edifice within Port Foster, the so-called Stanley Patch. Geophysical data traced the volcano and characterized its morphology and inner structure. Underwater scuba sampling allowed to acquire sediment and rock samples, photographs and video images of the benthic organisms and seascape. Morphology of Stanley Patch cone and textural characteristics of the collected pyroclastic rocks indicate that the volcanic edifice was originated during an explosive eruption. Furthermore, the lack of palagonitization, quenched pyroclast margins, and hyaloclastite deposits indicate that this cone has formed on-land, before the caldera floor became inundated by the seawater, highlighting the complex intra-caldera evolution of Deception Island. A sediment core from the crater was collected for sedimentological, and geochemical analysis. Antarctic climate and seasonal sea ice, together with organic degradation due to high sedimentation rates, explain the low total organic carbon data measured. The volcanic history of the island has probably avoided the development of a stable benthic community over time, similar to other Antarctic shallow communities. Moreover, the current geomorphological conditions still shape different benthic communities than in the surrounding coastal ecosystems. Stanley Patch, and the whole Port Foster, provide a natural laboratory for benchmarking the reestablishment of benthic communities on a volcanic-influenced shallow marine environment, offering relevant data for future studies evaluating global climate change effects on the Antarctic seabed., SCOPUS: ar.j, info:eu-repo/semantics/published

Sea-level change is thought to influence the frequencies of volcanic eruptions on glacial to interglacial timescales. However, the underlying physical processes and their importance relative to other influences (for example, magma recharge rates) remain poorly understood. Here we compare an approximately 360-kyr-long record of effusive and explosive eruptions from the flooded caldera volcano at Santorini (Greece) with a high-resolution sea-level record spanning the last four glacial–interglacial cycles. Numerical modelling shows that when the sea level falls by 40 m below the present-day level, the induced tensile stresses in the roof of the magma chamber of Santorini trigger dyke injections. As the sea level continues to fall to −70 or −80 m, the induced tensile stress spreads throughout the roof so that some dykes reach the surface to feed eruptions. Similarly, the volcanic activity gradually disappears after the sea level rises above −40 m. Synchronizing Santorini’s stratigraphy with the sea-level record using tephra layers in marine sediment cores shows that 208 out of 211 eruptions (both effusive and explosive) occurred during periods constrained by sea-level falls (below −40 m) and subsequent rises, suggesting a strong absolute sea-level control on the timing of eruptions on Santorini—a result that probably applies to many other volcanic islands around the world. Sea-level lowstands over the last 360,000 years strongly controlled the timing of eruptions of the Santorini Volcano, according to an analysis of tephras and sea-level records, as well as numerical modelling of the underlying magma chamber.

For nearly 1300 years Stromboli has been renowned not only for its continuous degassing activity and mild explosions at the summit craters, but also for short-lived, violent explosive events of variable scale known as major explosions and paroxysms. It is important to understand the triggering mechanisms of paroxysms, as this violent explosive activity can impact social and economic life on the island. To this end, we focus on the 1456 and 1930 paroxysms and on the most recent events, in July and August 2019. We present new data on the geochemistry of the 2019 bulk pumice, along with a compilation of data from the literature, chemical profiles in olivine crystals, and the physical parameters of explosive eruptions of wide ranging magnitude and intensity. Trace element concentrations (Nb, La and Ba) and ratios (Rb/Th) indicate that the 2019 pumice samples plot in the domain of magma batches erupted within the last 20 years at Stromboli. As a whole, there is no correlation between magma geochemistry and magnitude or intensity of explosive eruptions, which span a range of ~3 orders of magnitude (from major explosions to large paroxysms) based on estimates of erupted tephra volumes. In contrast, olivine compositions are a good proxy for total tephra volumes, suggesting that the magma source can affect the magnitude and intensity of the final eruption. They also indicate that in July 2019 the plumbing system reached steady-state conditions prior to paroxysm, whereas olivine and clinopyroxene zoning in products from the August 2019 paroxysm testifies to magma recharge. For small and large paroxysms, timescales were derived from Fe-Mg diffusion profiles in olivine. In both types of explosion, the last phases of crystallization indicate rapid magma ascent rates two to ten days prior to eruption. Lastly, we discuss the possible relative influence on eruption dynamics of flank collapse, lava outpouring through fractures opening, and partial emptying of the shallow conduits. These phenomena may enhance volatile-rich magma ascent by increasing the decompression rate, although pressurization of the crustal system and the deep refilling by magma and its CO2-rich gas phase play a major role in triggering paroxysms.

SLE was funded by the Global Geological Risk Research Platform of the British Geological Survey NC-ODA grant NE/R000069/1: Geoscience for Sustainable Futures. Understanding the location, intensity, and likely duration of volcanic hazards is key to reducing risk from volcanic eruptions. Here, we use a novel near-real-time dataset comprising Volcanic Ash Advisories (VAAs) issued over 10 years to investigate global rates and durations of explosive volcanic activity. The VAAs were collected from the nine Volcanic Ash Advisory Centres (VAACs) worldwide. Information extracted allowed analysis of the frequency and type of explosive behaviour, including analysis of key eruption source parameters (ESPs) such as volcanic cloud height and duration. The results reflect changes in the VAA reporting process, data sources, and volcanic activity through time. The data show an increase in the number of VAAs issued since 2015 that cannot be directly correlated to an increase in volcanic activity. Instead, many represent increased observations, including improved capability to detect low- to mid-level volcanic clouds (FL101–FL200, 3–6 km asl), by higher temporal, spatial, and spectral resolution satellite sensors. Comparison of ESP data extracted from the VAAs with the Mastin et al. (J Volcanol Geotherm Res 186:10–21, 2009a) database shows that traditional assumptions used in the classification of volcanoes could be much simplified for operational use. The analysis highlights the VAA data as an exceptional resource documenting global volcanic activity on timescales that complement more widely used eruption datasets. Publisher PDF

Dense, vitric, dacitic pyroclasts (dacite lithics) from the 1991 preclimactic explosions of Mt. Pinatubo were analyzed for their vesicular and crystal textures and dissolved H2O and CO2 contents. Micron-scale heterogeneities in groundmass glass volatile contents (0.9 wt% differences in H2O within 500 μm) are observed and argue that parts of the dacite lithics equilibrated at different depths before finally being constructed. Greater vesicularities and larger and greater number densities of vesicles are observed in groundmass glass around phenocrysts compared to groundmass glass away from phenocrysts, similar to textures produced in experiments that sintered bimodal distributions of particles. Furthermore, increasingly greater proportions of stretched and distorted vesicles are observed in lithics from the later explosions, which parallels the increasingly shorter reposes between explosions. Finally, micron-sized crystal fragments are ubiquitous in groundmass glass of all dacite lithics. The textures, together with the variable volatile contents, lead us to propose a model that the dacite lithics formed by rapid and repetitive sintering of ash particles derived from a variety of depths on the conduit walls above the fragmentation level. We speculate that sintering of conduit material produced impermeable layers that retarded gas flow through the conduit, causing pressure to build until the cap failed and the next explosion occurred.

Magma from Plinian volcanic eruptions contains an extraordinarily large numbers of bubbles. Nucleation of those bubbles occurs because pressure decreases as magma rises to the surface. As a consequence, dissolved magmatic volatiles, such as water, become supersaturated and cause bubbles to nucleate. At the same time, diffusion of volatiles into existing bubbles reduces supersaturation, resulting in a dynamical feedback between rates of nucleation due to magma decompression and volatile diffusion. Because nucleation rate increases with supersaturation, bubble number density (BND) provides a proxy record of decompression rate, and hence the intensity of eruption dynamics. Using numerical modeling of bubble nucleation, we reconcile a long-standing discrepancy in decompression rate estimated from BND and independent geospeedometers. We demonstrate that BND provides a record of the time-averaged decompression rate that is consistent with independent geospeedometers, if bubble nucleation is heterogeneous and facilitated by magnetite crystals., The authors simulate bubble nucleation in silica-rich magma with conditions appropriate for Plinian eruptions. They demonstrate that the gap between decompression rate estimates from bubble number density and independent geospeedometers can be largely closed if nucleation is heterogenous facilitated by magnetite crystals and decompression rate is calculated as time-averaged values.

Eruption source parameters (in particular erupted volume and column height) are used by volcanologists to inform volcanic hazard assessments and to classify explosive volcanic eruptions. Estimations of source parameters are associated with large uncertainties due to various factors, including complex tephra sedimentation patterns from gravitationally spreading umbrella clouds. We modify an advection-diffusion model to investigate this effect. Using this model, source parameters for the climactic phase of the 2450 BP eruption of Pululagua, Ecuador, are different with respect to previous estimates (erupted mass: 1.5–5 × 1011 kg, umbrella cloud radius: 10–14 km, plume height: 20–30 km). We suggest large explosive eruptions are better classified by volume and umbrella cloud radius instead of volume or column height alone. Volume and umbrella cloud radius can be successfully estimated from deposit data using one numerical model when direct observations (e.g., satellite images) are not available. Total erupted volume and umbrella cloud radius can inform estimates of eruption characteristics and volcanic explosivity more reliably than column height or volume alone, according to simulations of the eruption of Pululagua, Ecuador, 2,450 years ago.

Assessing the potential and likelihood of explosive eruptions is vital for almost 800 million people living near active volcanoes. Magma reservoirs are not directly accessible, limiting our capability to understand the prerequisites for an explosive eruption and our ability to perform experiments that simulate magmatic processes at depth. Therefore, deciphering volcanic precursors is key to forecasting volcanic eruptions. In this study, we used synchrotron-based X-ray tomographic microscopy to observe felsic magma vesiculation at high temperature (1,100°C) to establish the pre-eruptive conditions that favor explosive activity. Specifically, we studied the increase of seismic attenuation with increasing gas content during magma vesiculation. These results are applied to the natural range of volcanic tremors (0.2–5 Hz) to detect the proximity of gas-charged magma to the surface prior to volcanic eruption: gas-rich, crystal- free felsic magmas are detected at larger depth (40 MPa) than gas-rich, crystal-bearing systems (10 MPa).

The magnitude and intensity of the 60 CE Cretaio Tephra, the largest historical explosive eruption at Ischia caldera (Italy), was studied integrating field data and numerical modelling in order to reconstruct the dispersal of the fallout related to the climax phase of the eruption and characterize its physical parameters. A field survey of the main fall unit (EUC) of Cretaio Tephra and its sampling was performed on the island, which is the proximal area of dispersal, and for the first time outcrops of this tephra were found southward on the Capri Island. The dataset is completed by a distal tephra sampled in the offshore and described in the literature, allowing the analysis of samples of intermediate and distal deposits. Grain size analysis of the samples collected on the island show bimodal distributions due to the presence of a ballistic component, especially in the most proximal sampling sites around the inferred and buried vent. Tails of fine ash in the distributions can be associated with settling enhanced by ash aggregation processes in the moisture-rich plume. Tephra dispersal was reconstructed using the HAZMAP tephra dispersal model by minimizing the difference between the simulations obtained exploring plausible ranges of eruption source parameters and the available thickness and grain-size measurements. Results show that the dispersal axis of EUC is to the south-southeast, the best guess for the total erupted volume of tephra is 0.075 km3, the plume height ranges between 5 and 13 km, for an average mass eruption rate (MER) of 105 kg/s, hence a duration of the eruption of a few days. Considering an eruptive scenario given by the eruption parameters and diffusion coefficient of the Cretaio Tephra, together with a statistical set of wind profiles, HAZMAP modelling allowed us to generate tephra loading probability maps, needed to assess the impact of such an eruption at Ischia Island and the Neapolitan metropolitan area, pivotal for civil protection purposes. Another important outcome of the study is that, for volcanic islands, the reconstruction of eruption parameters may benefit much more from the search of even few medial and distal offshore outcrops than from implementing the on-island proximal dataset only.

Pyroclastic deposits of volcanic explosive eruptions are associated with both sedimentation of tephra and emplacement of pyroclastic density currents (PDCs) that travel on the flank of volcanoes. Pyroclastic deposits are typically mixtures of ash, lapilli and blocks, very loose and unconsolidated, hence prone to move along a slope. Due to highly porous structure, such deposits are also prone to wetting induced collapse, with a transition from a solid-like behaviour to a fluid-like behaviour. It entails a long run-out of mass-movements (landslides or lahars and debris flows) eventually triggered. Disasters associated with this type of deposit remobilization have been recorded all over the world even decades or centuries after the end of an eruption. Here we provide new insights into remobilization of tephra deposits based on various international case studies, bridging a gap among the different dataset and interpretations. Exponential and power relations are found among the uniformity coefficient, the median diameter and the main physical variables adopted in the physical-based models used for the analysis of the natural hazards in volcanic deposits.

Dense, glassy pyroclasts found in products of explosive eruptions are commonly employed to investigate volcanic conduit processes through measurement of their volatile inventories. This approach rests upon the tacit assumption that the obsidian clasts are juvenile, that is, genetically related to the erupting magma. Pyroclastic deposits within the Yellowstone-Snake River Plain province almost without exception contain dense, glassy clasts, previously interpreted as hyaloclastite, while other lithologies, including crystallised rhyolite, are extremely rare. We investigate the origin of these dense, glassy clasts from a coupled geochemical and textural perspective combining literature data and case studies from Cougar Point Tuff XIII, Wolverine Creek Tuff, and Mesa Falls Tuff spanning 10 My of silicic volcanism. These results indicate that the trace elemental compositions of the dense glasses mostly overlap with the vesiculated component of each deposit, while being distinct from nearby units, thus indicating that dense glasses are juvenile. Textural complexity of the dense clasts varies across our examples. Cougar Point Tuff XIII contains a remarkable diversity of clast appearances with the same glass composition including obsidian-within-obsidian clasts. Mesa Falls Tuff contains clasts with the same glass compositions but with stark variations in phenocryst content (0 to 45%). Cumulatively, our results support a model where most dense, glassy clasts reflect conduit material that passed through multiple cycles of fracturing and sintering with concurrent mixing of glass and various crystal components. This is in contrast to previous interpretations of these clasts as entrained hyaloclastite and relaxes the requirement for water-magma interaction within the eruptive centres of the Yellowstone-Snake River Plain province., Bulletin of Volcanology, 83 (4), ISSN:0258-8900, ISSN:1432-0819

Arc magmas typically contain phenocrysts with complex zoning and diverse growth histories. Microlites highlight the same level of intracrystalline variations but require nanoscale resolution which is globally less available. The southern Taupo Volcanic Zone (TVZ), New Zealand, has produced a wide range of explosive eruptions yielding glassy microlite-bearing tephras. Major oxide analyses and textural information reveal that microlite rims are commonly out of equilibrium with the surrounding glass. We mapped microlites and microcrysts at submicron resolution for major and trace element distributions and observed three plagioclase textural patterns: (1) resorption and overgrowth, (2) oscillatory zoning, and (3) normal (sharp) zoning. Pyroxene textures are diverse: (1) resorption and overgrowth, (2) calcium-rich bands, (3) hollow textures, (4) oscillatory zoning, (5) sector zoning, (6) normal zoning and (7) reverse zoning. Microlite chemistry and textures inform processes operating during pre-eruptive magma ascent. They indicate a plumbing system periodically intruded by short-lived sub-aphyric dykes that entrain microantecrysts grown under diverse physico-chemical conditions and stored in rapidly cooled, previously intruded dykes. Changes in temperature gradients between the intrusion and the host rock throughout ascent and repeated magma injections lead to fluctuations in cooling rates and generate local heterogeneities illustrated by the microlite textures and rim compositions. Late-stage degassing occurs at water saturation, forming thin calcic microcryst rims through local partitioning effects. This detailed investigation of textures cryptic to conventional imaging shows that a significant proportion of the micrometre-sized crystal cargo of the TVZ is of antecrystic origin and may not be attributed to late-stage nucleation and growth at the onset of volcanic eruptions, as typically presumed.

Most basaltic explosive eruptions intensify abruptly, allowing little time to document processes at the start of eruption. One opportunity came with the initiation of activity from fissure 8 (F8) during the 2018 eruption on the lower East Rift Zone of Klauea, Hawaii. F8 erupted in four episodes. We recorded 28 minutes of high-definition video during a 51-minute period, capturing the onset of the second episode on 5 May. From the videos we were able to analyze the following in-flight parameters: frequency and duration of explosions; ejecta heights; pyroclast exit velocities; in-flight total mass and estimated mass eruption rates; and the in-flight total grain size distributions. Videos record a transition from initial pulsating outgassing, via spaced, but increasingly rapid, discrete explosions, to quasi-sustained, unsteady fountaining. This transition accompanied waxing intensity (mass flux) of the F8 eruption. We infer that all activity was driven by a combination of the ascent of a coupled mixture of small bubbles and melt, and the buoyant rise of decoupled gas slugs and/or pockets. The balance between these two types of concurrent flow determined the exact form of the eruptive activity at any point in time, and changes to their relative contributions drove the transition we observed at early F8. Qualitative observations of other Hawaiian fountains at Klauea suggest that this physical model may apply more generally. This study demonstrates the value of in-flight parameters derived from high resolution videos, which offer a rapid and highly time-sensitive alternative to measurements based on sampling of deposits post-eruption.

The evolution of volcanic sulfur and the resulting radiative forcing following explosive volcanic eruptions is well understood. Petrological evidence suggests that significant amounts of halogens may be co-emitted alongside sulfur in some explosive volcanic eruptions, and satellite evidence indicates that detectable amounts of these halogens may reach the stratosphere. In this study, we utilise an aerosol–chemistry–climate model to simulate stratospheric volcanic eruption emission scenarios of two sizes, both with and without co-emission of volcanic halogens, in order to understand how co-emitted halogens may alter the life cycle of volcanic sulfur, stratospheric chemistry, and the resulting radiative forcing. We simulate a large (10 Tg of SO2) and very large (56 Tg of SO2) sulfur-only eruption scenario and a corresponding large (10 Tg SO2, 1.5 Tg HCl, 0.0086 Tg HBr) and very large (56 Tg SO2, 15 Tg HCl, 0.086 Tg HBr) co-emission eruption scenario. The eruption scenarios simulated in this work are hypothetical, but they are comparable to Volcanic Explosivity Index (VEI) 6 (e.g. 1991 Mt Pinatubo) and VEI 7 (e.g. 1257 Mt Samalas) eruptions, representing 1-in-50–100-year and 1-in-500–1000-year events, respectively, with plausible amounts of co-emitted halogens based on satellite observations and volcanic plume modelling. We show that co-emission of volcanic halogens and sulfur into the stratosphere increases the volcanic effective radiative forcing (ERF) by 24 % and 30 % in large and very large co-emission scenarios compared to sulfur-only emission. This is caused by an increase in both the forcing from volcanic aerosol–radiation interactions (ERFari) and composition of the stratosphere (ERFclear,clean). Volcanic halogens catalyse the destruction of stratospheric ozone, which results in significant stratospheric cooling, offsetting the aerosol heating simulated in sulfur-only scenarios and resulting in net stratospheric cooling. The ozone-induced stratospheric cooling prevents aerosol self-lofting and keeps the volcanic aerosol lower in the stratosphere with a shorter lifetime. This results in reduced growth by condensation and coagulation and a smaller peak global-mean effective radius compared to sulfur-only simulations. The smaller effective radius found in both co-emission scenarios is closer to the peak scattering efficiency radius of sulfate aerosol, and thus co-emission of halogens results in larger peak global-mean ERFari (6 % and 8 %). Co-emission of volcanic halogens results in significant stratospheric ozone, methane, and water vapour reductions, resulting in significant increases in peak global-mean ERFclear,clean (> 100 %), predominantly due to ozone loss. The dramatic global-mean ozone depletion simulated in large (22 %) and very large (57 %) co-emission scenarios would result in very high levels of UV exposure on the Earth's surface, with important implications for society and the biosphere. This work shows for the first time that co-emission of plausible amounts of volcanic halogens can amplify the volcanic ERF in simulations of explosive eruptions. It highlights the need to include volcanic halogen emissions when simulating the climate impacts of past or future eruptions, as well as the necessity to maintain space-borne observations of stratospheric compounds to better constrain the stratospheric injection estimates of volcanic eruptions.

Active volcanoes continuously register morphological changes during their activity by the emplacement of lava flows and pyroclastic loose material on their flanks. Precipitation represents an external agent that reshapes the volcano edifice by remobilizing large volumes of ash and pyroclastic flow deposits producing lahars, sediment-water, or/and gravity-driven flows. Depending on the regional climatic conditions, lahars can be a very common phenomenon, highly frequent just after an eruption episode and they can persist for several years. The most common lahar initiation mechanism corresponds to the progressive water erosion of material from the catchment and the riverbed, up to bulk to a saturated mixture of sediment and water. Precipitation duration and intensity are the main factors in lahar generation. Orographic (or stationary) and regional (o migratory) rain events can both trigger lahars. In the first case, high intensity, short duration rains trigger low-volume (10*4–10*5 m3), low-duration (less than one hour) lahars; in contrast, extreme hydrometeorological events such hurricanes can trigger large volume (10*6 m3) and long-duration (several hours) lahars with catastrophic effects on the surrounding area. The hydrological response of the watershed feeding the ravine is a key factor in determining flow volume, flow discharge behavior, and morphological evolution of the drainage. On the other hand, during cataclysmic eruptions, with the formation of long-lasting, sustained eruptive columns, atmospheric conditions can rapidly change at the regional scale, inducing rainfall that can quickly trigger syneruptive lahars also promoted by the accumulation of fine ash layers on the volcano slopes with hydrophobic behavior. In addition, the large amounts of SO2 gas released during catastrophic explosive eruption can induce climate changes, with an important impact on the Global Monson rainfalls, changing their distribution for a few years, on a global scale. Studying the interaction between volcanic activity and precipitation will help to understand and model lahar initiation processes and their behavior and will allow to establish more accurately future hazard scenarios.

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

The eruption of volcanoes appears one of the most unpredictable phenomena on Earth. Quantification of the eruptive record constrains what is possible in a volcanic system. Timing is the hardest part to quantify. One of the main processes triggering explosive eruptions is the refilling of a sub-volcanic magma chamber by a new magma coming from depth. This process results in mixing and provokes a time-dependent diffusion of chemical elements. An eruption can initiate at any time during this process. Magma mixing is then frozen in time by the eruption. The time elapsed between mixing and eruption is recorded into the compositional patterns of the rocks. In this chapter we discuss a possible method that might help us cutting the Gordian knot of the presently intractable problem of volcanic eruption timing using a surgical approach integrating geochemical and experimental data on magma mixing. If these timescales can be linked with geophysical signals occurring prior to eruptions, the approach presented here may equip us with a new conceptual framework to move further steps towards one of the key objectives of volcanology: the prediction of volcanic eruptions.

In the world, volcanic systems exhibit a wide range of eruption styles threatening the lives of millions of people. Relatively slow effusive eruptions generate lava flows (low viscosity magma) and lava domes (high viscosity magma) and tend to evolve over days to decades. Alternatively, explosive eruptions can inject very large volumes of fragmented magma and volcanic gas high into the atmosphere over shorter periods (minutes to weeks to months). Mitigation of the associated risk to populations, the built environment, and the cultural heritage relies upon our ability to accurately assess volcanic hazards, and this, in turn, depends on our understanding of the processes that control the style and scale of volcanic eruptions. To this end, technological developments over the last couple of decades have greatly improved our ability to characterize magmatic systems and detect precursors at high spatial and temporal resolution through the use of analytical and observational volcanology, including monitoring-derived data, and volcano geophysics. Numerical modeling of magma ascent can serve to link all of these data and processes to build effective near-real-time strategies. The complexity of the volcanic system, derived from the multiphase, multicomponent character of the magmatic mixtures and from their interaction dynamics with the surrounding host rocks, is however manifested in the complexity of its mathematical representation, and numerical models able to describe several interdependent processes, eventually at disequilibrium conditions, are required to capture the nature of volcanic systems with fidelity. In this chapter, we present the main equations governing magma ascent, highlighting the multiphase and disequilibrium nature of volcanic flows, and the presence of complex feedback mechanisms between gas exsolution, outgassing, and crystallization that are able to influence the most important characteristics of the resulting volcanic events. Then, a suite of numerical simulations is described to show the effect of some parameters and processes in controlling eruption style and scale, and thus the potential eruption hazard.

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.

International audience; Eruptive columnmodels are powerful tools for investigating the transport of volcanic gas and ash, reconstructing past explosive eruptions, and simulating future hazards. However, the evaluation of these models is challenging as it requires independent estimates of themainmodel inputs (e.g.mass eruption rate) and outputs (e.g. column height). There exists no database of independently estimated eruption source parameters (ESPs) that is extensive, standardized, maintained, and consensus-based. This paper introduces the Independent Volcanic Eruption Source Parameter Archive (IVESPA, ivespa.co.uk), a community effort endorsed by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Commission on Tephra HazardModelling.We compiled data for 134 explosive eruptive events, spanning the 1902-2016 period, with independent estimates of: i) total erupted mass of fall deposits; ii) duration; iii) eruption column height; and iv) atmospheric conditions. Crucially, we distinguish plume top versus umbrella spreading height, and the height of ash versus sulphur dioxide injection. All parameter values provided have been vetted independently by at least two experts. Uncertainties are quantified systematically, including flags to describe the degree of interpretation of the literature required for each estimate. IVESPA also includes a range of additional parameters such as total grain size distribution,eruption style, morphology of the plume (weak versus strong), and mass contribution from pyroclastic density currents, where available. We discuss the future developments and potential applications of IVESPA and make recommendations for reporting ESPs to maximize their usability across different applications. IVESPA covers an unprecedented range of ESPs and can therefore be used to evaluate and develop eruptive column models across a wide range of conditions using a standardized dataset.

Silicic calderas globally tend to record a cyclic magmatic, structural, and eruptive evolutionary progression. Some calderas are polycyclic, involving multiple catastrophic collapses in the same approximate location. Here we discuss five examples from well-studied, geologically-young and active magmatic systems: The Kos-Nisyros Volcanic Complex (Greece), Long Valley (USA), Campi Flegrei (Southern Italy), Rabaul (Papua New Guinea), and Okataina (New Zealand) in order to gain insights on the inner workings of caldera systems during the build up to and recovery from large explosive eruptions. We show that the sub-caldera magmatic system evolves through a series of processes, here collectively termed “caldera cycle”, that are common to monocyclic and polycyclic calderas. In the case of polycyclic calderas, they accompany the transition from one caldera-forming eruption to the next. The caldera cycle comprises (1) the period of pre-collapse activity (incubation, maturation, widespread presence of a magmatic volatile phase), (2) the catastrophic caldera-forming (CCF) eruption, and (3) post-collapse recovery (resurgence, renewed eruptions, subsequent maturation) or the possible cessation of the cycle. The incubation phase corresponds to a period of thermal maturation of the crust, during which eruptions are frequent and of small volume due to the limited capability of reservoirs to grow. During the maturation phase, magma reservoirs gradually grow, coalesce, homogenize, magmas differentiate, and eruption frequency decreases. The system transitions into the fermentation phase once an exsolved magmatic volatile phase is continuously present in the reservoir, thereby increasing the compressibility of the magma and instigating a period of runaway growth of the reservoir. A CCF eruption at the end of the fermentation phase could be the concatenated result of multiple magmatic processes (including magma recharge, volatile exsolution, and crystal mush remelting) pressurizing the reservoir, while external factors (e.g., tectonic processes) can also play a role. Postcaldera eruptions, subvolcanic intrusions, and hydrothermal activity typically continue, even if the magma supply wanes. If, however, magma supply at depth remains substantial, the system may recover, initially erupting the remobilized remains of the CCF reservoir and/or new recharging magmas until a shallow reservoir starts to grow and mature again. Placing other calderas worldwide within this framework would enable to test the robustness of the proposed framework, deepen the understanding of what controls the duration of a cycle and its individual phases, and refine the petrologic, geophysical, and unrest symptoms that are characteristic of the state of a system., Earth-Science Reviews, 218

A main challenge in open conduit volcanoes is to detect and interpret the ultra-small strain ( after the flank eruption of December 2018, Etna generated a violent and spectacular eruptive sequence of lava fountains. There were 23 episodes from December 13, 2020 to March 31, 2021, 17 of which in the brief period 16 February to 31 March with an intensified occurrence rate. The high-precision borehole dilatometer network recorded significant strain changes in the forerunning phase of December 2020 accompanying the final magma migration at the shallower levels, and also during the single lava fountains and during the entire sequence. The source modeling provided further information on the shallow plumbing system. Moreover, the strain signals also gave useful information both on the explosive efficiency of the lava fountains sequence and the estimate of erupted volume. The high precision borehole dilatometers confirm to be strategic and very useful tool, also to detect and interpret ultra-small strain changes associated with explosive eruptions, such as lava fountains, in open conduit volcanoes.

Evidence for frequent, large landslides on the flanks of the volcanic edifices forming the Canary Islands include outstanding landslide scars and their correlative submarine and subaerial rock and debris avalanche deposits. These landslides involved volumes ranging from tens to hundreds of km3. The sudden entry of large volumes of rock masses in the sea may have triggered tsunamis capable of affecting the source and neighboring islands, with the resulting huge waves dragging coastal and seabed materials and fauna and redepositing them inland. Here, we present new geological evidence and geochronological data of at least five megatsunamis in Tenerife, Lanzarote, and Gran Canaria, triggered by island flank megalandslides, and occasionally explosive eruptions, during the last 1 million years. The exceptional preservation of the megatsunami deposits and the large area they cover, particularly in Tenerife, provide fundamental data on the number of tsunami events and run-ups, and allow proposals on the sources and age of the tsunamis. Tsunami run-up heights up to 290 m above coeval sea level, some of the highest known on Earth in recent geological times, were estimated based on sedimentological, geomorphological, paleontological, and geochronological data. The research results made it possible to estimate the recurrence of tsunamis in the archipelago during the last hundreds of thousands of years, and to establish relationships between tsunami deposits and the probable triggering island flank landslides.

The youngest (last 1500 years) volcanic eruptions of Lipari, within the Aeolian Archipelago, produced the prominent pumice cone of Monte Pilato and the obsidian lava flows of Rocche Rosse and Forgia Vecchia, concentrated in the north-eastern sector of the island as well as highly dispersed white-coloured, fine-grained tephra layers of rhyolitic composition in terrestrial and marine settings on the regional scale. Here we describe in detail the stratigraphy of pyroclastic successions and lava flows erupted by different vents - Monte Pilato, Forgia Vecchia, Lami, and Rocche Rosse - combining field observations, sedimentological characteristics of the tephra deposits, and major and trace element compositions of the volcanic glass. All the pyroclastic materials consist of aphyric pumice lapilli and ash with a largely homogeneous rhyolitic composition. The Monte Pilato and Forgia Vecchia deposits primarily consist of highly vesicular pumice fragments and subordinate obsidian clasts, whilst Rocche Rosse and Lami are characterized by moderately vesicular juvenile fragments with a more significant fraction of obsidian. The Lami tephra also contains peculiar pumice clasts with a fibrous texture and breadcrust bombs. Stratigraphic relationships, and paleomagnetic and 14C ages of the lava and pyroclastic deposits are combined with the archaeological information and historical reports, enabling us to provide an accurate chrono-stratigraphic framework for the youngest eruptions of Lipari. Following the 8th century CE eruption of Monte Pilato, which produced a pumice cone and a obsidian lava flow, activity resumed in the second half of 13th century CE with the explosive eruption of Forgia Vecchia that culminated in the emission of a bilobate obsidian lava flow. This eruption was shortly followed by the explosive eruptions of Lami and Rocche Rosse, the latter concluded with the emission of the widely renowned obsidian lava flow. By integrating stratigraphy and geochemistry of tephra deposits with a new chronological scheme, our work facilitates the refinement of proximal-to-distal correlation of Lipari's rhyolitic tephra in continental marine environments of the central Mediterranean area in the last 1500 years. A fine-grained, rhyolitic ash found on Stromboli (~40 km NE from Lipari) has an origin from the Monte Pilato and thus, constrains tephra dispersion towards the NE. Very similar ash beds dispersed southwards and interlayered within the near-source deposits of La Fossa, Vulcano island (~10 km from Lipari) exhibit features that are consistent with the younger activities of the Rocche Rosse eruption. A possible link between previously identified rhyolitic ash layers identified in marine cores of the Ionian Sea and the Forgia Vecchia eruption are postulated, although the age and textural characteristics of these distal tephra are not univocal in indicating a correlation to either Monte Pilato or Forgia Vecchia.