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Geophysical data provide the chance to investigate a volcano's dynamics; considerable information can especially be gleaned on the stress and strain patterns accompanying the internal processes and the effect of magma ascent on the main structures triggering earthquakes. Here, we analysed in detail the seismicity recorded over the last two decades on Etna volcano (southern Italy), focusing on earthquakes distribution and focal mechanism clustering; the ground deformation pattern affecting the volcanic edifice with the inflation and deflation phases was also examined. Analysed data were compared in order to shed light on possible relationships with the volcanic activity and to better understand the internal dynamics of the volcano over time. Significant steps during or shortly before major eruptions in the seismic strain release and ground deformation temporal series highlight a straightforward relationship between seismicity occurring at shallow level, inflation/deflation and volcanism. Furthermore, at depths greater than 5–7 km, down to about 20 km, the orientation of the P- and T-axes clearly indicate the existence of a pressure source in the central part of the volcano. All the results underline that the stress field related to the volcano plumbing system interferes with the regional field, partly overriding it. [ABSTRACT FROM AUTHOR]

Mount Somma–Vesuvius is a stratovolcano that represents a geological hazard to the population of the city of Naples and surrounding towns in southern Italy. Historically, volcanic eruptions at Mt. Somma–Vesuvius (SV) include high-magnitude Plinian eruptions, such as the infamous 79 CE eruption that occurred after 295 years of quiescence and killed thousands of people in Pompeii and surrounding towns and villages. The last eruption at SV was in 1944 and showed a Volcanic Explosivity Index (VEI) of 3 (0.01 km 3 of volcanic material erupted). Following the 1944 eruption, SV has been dormant for the past nearly 79 years, with only minor fumarolic and seismic activity. During its long history, centuries of dormancy at SV have ended with Plinian eruptions (VEI 6) that signal the beginning of a new cycle of eruptive activity. Thus, the current dormancy stage demands a need to better understand the mechanism involved in high-magnitude eruptions in order to better predict future eruption magnitude and style. Despite centuries of research on the SV volcanic system, many questions remain, including the evolution of magmatic volatiles from deep primitive magmas to shallower more evolved magmas. Developing a better understanding of the physical and chemical processes associated with volatile evolution at SV can provide insights into magma dynamics and the mechanisms that trigger highly explosive eruptions at SV. In this study, we present new data for the pre-eruptive volatile contents of magmas associated with four Plinian and two inter-Plinian eruptions at SV based on analyses of reheated melt inclusions (MIs) hosted in olivine. We correct the volatile contents of bubble-bearing MIs by taking into account the volatile contents of bubbles in the MIs. We recognize two groups of MIs: one group hosted in high-Fo olivine (Fo 85–90) and relatively rich in volatiles and the other group hosted in low-Fo olivine (Fo 70–69) and relatively depleted in volatiles. The correlation between volatile contents and compositions of host olivines suggests that magma fractionation took place under volatile-saturated conditions and that more differentiated magmas reside at shallower levels relative to less evolved/quasi-primitive magmas. Using the CO 2 contents of corrected MIs hosted in Fo 90 olivine from SV, we estimate that 347 to 686 t d -1 of magmatic CO 2 exsolved from SV magmas during the last 3 centuries (38–75 Mt in total) of volcanic activity. Although this study is limited to only few SV magmas, we suggest that further study applying similar methods could shed light on the apparent lack of correlation between the volatile contents of MIs and the style and age of eruptions. Further, such studies could provide additional constraints on the origin of CO 2 and the interaction between the carbonate platform and ascending magmas below SV. [ABSTRACT FROM AUTHOR]

The most frequent volcanic eruptions are of low-intensity and small magnitude. They produce abundant ash-sized (< 2 mm) clasts, which are too small to establish quantitative links between magmatic processes and eruptive dynamics using classic approaches. This inhibits our ability to study the past behaviour of frequently erupting volcanoes, essential to predict their future activity and mitigate their impact. The Palizzi unit (10–13th century, Vulcano, Italy) includes a prototype sequence of ash deposits resulting from prolonged Vulcanian eruptions punctuated by those of two larger sub-Plinian events. We apply Hierarchical Clustering to chemical analyses of clinopyroxene collected along the stratigraphy to decipher magma dynamics during this eruptive period. We identify periods of magma input and we link deep magmatic processes to eruptive dynamics, also showing that our approach can be used to connect magma and eruptive dynamics in any volcanic sequence. This is essential to track the processes occurring during frequent eruptions and to identify the build-up to larger explosive events. [ABSTRACT FROM AUTHOR]

Models of volcanic collapses proposed in the literature rely on combining field examples with analogue and numerical modelling to connect superficial observables to sub-surface volcano-tectonic processes. However, the behaviour of such collapses in an already faulted and fractured medium needs to be better explored. We studied a complex array of normal and reverse faults within the central sector of the active Campi Flegrei caldera, where faults with centimeters-to-meters displacements are hosted in the La Pietra tuff (∼13.5 ka) and the overlying pyroclastic succession of the last ∼5.5 kyr. We analyzed the attitude, kinematics and throw of these structures, employing a UAV-based digital outcrop model. The analysis shows that antithetic normal and reverse faults form in the hanging wall of a pre-existing WNW striking, NNE-dipping master normal fault. Moving northward, the strike of the antithetic faults rotates from WNW to NNW directions, with the latter showing a right-lateral oblique component. The simultaneity and coherence of both kinematics and attitudes are verified by the throw analysis. We associated the formation of this array with the caldera-collapse phase of the Agnano-Monte Spina eruption (∼4.55 ka), which caused off-caldera faulting beyond the main collapsed area. Based on field data, we suggest that during peak caldera-forming phases, wider areas beyond the main caldera scarps can be involved in volcano-tectonic collapses in the presence of a pre-existing fault network and complex tapped reservoirs. This highlights the role of inherited structures in weakening the crust above the magma reservoir that can potentially increase the magnitude and duration of caldera-forming eruptions, as they may induce a broader roof rock subsidence, pressurizing wider regions of the sub-caldera magma system. • We studied a complex array of normal and reverse faults at Campi Flegrei caldera. • These faults occur in the hanging wall of a reactivated master normal fault. • Both normal and reverse faults accommodate the overall displacement. • The array formed during the Agnano Monte Spina Plinian eruption collapse phase. [ABSTRACT FROM AUTHOR]

Somma-Vesuvius (SV) is an active volcanic system in southern Italy that has generated Plinian eruptions during its history as the infamous 79 CE (Pompeii) eruption. Plinian eruptions produced airfall pumice deposits characterized by white pumice clasts in the lower half part, and by grey pumice clasts in the other upper half part. Plinian pyroclastic deposits are also characterized by the presence of skarn xenoliths. Previous studies on the fluid (FI) and melt inclusions (MI) in the Somma-Vesuvius (SV) skarn xenoliths have widely documented immiscibility between silicate melt and hydrosaline melt (±aqueous chloride-rich liquid‑carbonate/sulfate melt). In this study, we recognize a new type of MI namely composite melt inclusions (CMI) hosted in minerals of SV skarn xenoliths previously studied in the literature. In addition to a review of studies about skarn at SV, we present new microthermometric observations of CMI based on heating experiments using a heating stage. We heated CMI to complete homogenization at 1080 °C, and we cooled the CMI to simulate a natural sequence of phase appearances during magma cooling. At T around 1060 °C the CMI unmixes forming two different silicate melts. Upon further cooling at around 700 °C, the CMI show droplets of chloride immiscible liquids instantly nucleating. The cooling experiments of CMI from high-T are assumed to reproduce on a small scale the sequence of magma cooling prior to eruption below SV. In this case, magma could unmix before eruption forming two different silicate melts producing a chemically stratified reservoir. In support of our heating experiments results of CMI, the reprocessing of SV bulk rock compositions data highlights that magma feeding interplinian eruptions is Fe-and P-rich and Si-poor. In contrast, magma feeding Plinian eruptions is Si-rich and Fe-and P-poor. As experimental studies have demonstrated, immiscibility can occur when one melt is Fe-and P-rich and Si-poor, and the other is Si-rich and Fe-and P-poor and the transition between the two end members is not gradual, resulting in a gap of homogeneous intermediate melt. • Geochemical zonation of the Somma Vesuvius shallow magma chamber • Silicate liquid immiscibility in melt inclusions • Interactions occurring at the contact between magma and limestone country rocks • Magma differentiation by silicate liquids immiscibility • Syneruptive nucleation of unmixed droplets of nonsilicate liquids [ABSTRACT FROM AUTHOR]

Silicic volcanoes are increasingly understood to be underlain by crystal-rich and vertically extensive magma reservoirs within which disequilibrium is widespread. Observations from ignimbrite deposits demonstrate that silicic magma reservoirs are often compartmentalised and compositionally stratified. However, it is currently unclear whether the small (i.e., < 0.1 km3 dense rock equivalent) eruptions that dominate activity at many volcanoes, and peralkaline volcanoes in particular, are fed from similarly complex magma reservoirs as their larger counterparts. Here I report petrographic and geochemical observations from the products of a small peralkaline eruption on Pantelleria, Italy, with the aims of unravelling peralkaline magma assembly processes and evaluating the complexity of reservoirs feeding small silicic eruptions. Matrix glass and whole-rock compositions from the Khaggiar lava flow and Cuddia Randazzo pumice cone reveal that erupted magmas were assembled from at least three distinct magma types stored within a compartmentalised magma reservoir: trachytes, less-evolved pantellerites and evolved pantellerites. Chemical variability in the Khaggiar lava flow was created by at least three distinct processes: the accumulation of evolved macrocrysts into evolved pantellerites; the injection of trachytic magmas into less evolved pantellerites; and the accumulation of relatively primitive macrocrysts into trachytic magmas. Macrocryst textures indicate that both trachytic and pantelleritic domains of the magma reservoir experienced numerous recharge events prior to the one that ultimately triggered eruption. Overall, magmas forming the Khaggiar lava flow and Cuddia Randazzo pumice cone appear to have been assembled in analogous ways to those erupted in much larger events. My observations are in good agreement with those from other peralkaline volcanoes and confirm that magma mingling, crystal cannibalism and macrocryst entrainment are as ubiquitous in peralkaline systems as they are in their calc-alkaline counterparts. [ABSTRACT FROM AUTHOR]

• U-Pb CA-ID-TIMS dates of zircon from plumbing system of a Permian caldera. • Distribution of ages interpreted through a new zircon saturation model. • Relative decrease of zircon mass with time implies monotonic cooling. • Late peak in zircon crystallization indicates episodic increase in heat supply. • Evidence for open-system processes preserved in zircon record of super-eruptions. The emplacement history and thermal evolution of subvolcanic magma reservoirs determine their longevity, size, and ability to feed volcanic eruptions. As zircon saturation is dependent on melt temperature and composition, quantitative analysis of zircon age distributions provides insight into the timing and magnitude of intensive parameter variations during the lifetime of a magma reservoir. Here we present chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon crystallization ages and in-situ zircon trace-element geochemistry for a suite of caldera-related, coeval plutonic and volcanic units of the Permian Sesia Magmatic System (northern Italy). This dataset documents the protracted growth and evolution (∼1 Myr) of a voluminous (>1000 km3), upper crustal (3.5–2.0 kbar) silicic magma reservoir. Systematic changes in zircon composition with time reveal episodic intrusions of new magma into a single, progressively differentiating reservoir which was dominantly kept at high crystallinity conditions (>60 vol.%). The volcanic and plutonic units both show dispersed and heterogeneous CA-ID-TIMS age distributions. A stochastic, thermodynamics-based zircon saturation model accounting for fractional crystallization, recharge and thermal rejuvenation effects on zircon growth and stability in a rhyolitic magma body reproduces the observed distributions of zircon U-Pb ages. Model results suggest that zircon compositional variability and crystallization age heterogeneity, characteristic of the Sesia and other large silicic systems, distinguish open- and closed-system magmatic processes. Specifically, an increase of the mass of crystallized zircons over time is the hallmark of thermally and chemically mature magma reservoirs, capable of producing voluminous eruptions upon changes in the thermal and mechanical state of the system. Conversely, a decrease in crystallized zircon mass over time characterizes systems where crystallization dominates over magma mobility, hindering substantial mass release during eruptive events. We suggest that quantitative analyses of dispersed zircon crystallization age distributions obtained with high-precision techniques can be applied to the plutonic and volcanic record to identify mature silicic magma reservoirs whose properties and storage conditions allowed for catastrophic caldera-forming eruptions. This work provides the petrologic community with a new tool to investigate the genesis and evolution of zircon-bearing intermediate to silicic intrusive magmatism and caldera-forming volcanism through time and across tectonic settings. [ABSTRACT FROM AUTHOR]

Despite the many scientific contributions and advances in our understanding of magmatic processes that have been derived from the analyses of melt inclusions (MI), it is difficult to find examples of chronologically constrained MI, tracking a magma mixing event before an eruption. Here, we studied a single, reversely zoned olivine phenocryst with multiple MI from the Solchiaro eruption on Procida Island (Phlegrean Volcanic District, Southern Italy) to understand both the order of appearance of basaltic versus trachybasaltic magmas and the reliability of MI to record a magma mixing event. Based on phosphorous X-ray mapping, MI are characteristic of three populations: early, intermediate, and late MI. Early MI represent trachybasaltic melts which differentiate by fractional crystallization to form the liquids that are represented by intermediate MI. Late MI are hosted within a forsterite-rich growth band near the olivine rim representing a mixing event between basalts and the pre-existing trachybasaltic magmas shortly before the eruption. The compositions of the three MI populations are compared to a database of bulk rocks and MI from the literature on the mafic products of the Phlegrean Volcanic District to test if the MI studied show same geochemical trends. In addition, in this study, the late MI represented a melt inclusion assemblage (MIA) sensu stricto that represents a group of MI trapped all along the same growth band of the olivine. This simultaneous entrapment offers the opportunity to study the reliability of MI based on Roedder's rules. Correlations between major element contents and the size of late MI suggest that MI ≥22 μm are the most reliable in recording the compositions of the melt at specific times and places in the plumbing system. • We analyze MI hosed in an individual reversely zoned olivine. • We used phosphorous X-Ray mapping technique to assess relative ages of MI. • We recognized three different populations of MI each showing specific compositions. • Late MI trapped simultaneously and those <22 μm are the most reliable. [ABSTRACT FROM AUTHOR]

Apatite, which has demonstrated to be useful for tracking volatile evolution in magmatic systems, is a common accessory in La Fossa active volcano (Vulcano island, Italy) products. We performed in situ geochemical (major and trace elements, Cl, F, S) analyses on apatite of La Fossa, and used the data to track the pre-eruptive magmatic volatile evolution for the La Fossa shoshonitic suite, to provide insights on magma evolution in the plumbing system and to investigate volatile fluxing. Our results confirm that apatite volatile chemistry is a valuable tool to give constraints on pre-eruptive volatile contents of magmas. For specific compositions, however, we obtained an underestimation of the water contents with respect to those estimated with plagioclase-liquid hygrometer in previous works. Vulcano apatite halogen composition also indicates that water saturation and pre-eruptive exsolution of a hypersaline aqueous fluid phase occurred when the magma reached rhyolitic composition. The high As, Bi and Cd contents found in apatite crystals belonging to shoshonite and high-K trachyte suggest that the magma reservoirs feeding these eruptions were affected by a deep volatile fluxing which was able to carry these trace elements up to shallow levels. This is in agreement with the occurrence of the deep degassing already demonstrated at La Fossa volcano on the basis of petrological and geochemical data, and supports the apatite geochemical approach to track deep volatile fluxing. • Apatite chemistry is used to assess volatile evolution in Vulcano magmas. • Apatite halogen composition indicates hypersaline fluid exsolution in rhyolites. • High As, Bi, Cd contents in apatite suggest deep volatile fluxing. [ABSTRACT FROM AUTHOR]

Crustal-scale magmatic systems act as filters between the mantle and the atmosphere, and can generate large volcanic eruptions that pose significant hazards while altering Earth's climate. Quantifying the growth rates, magma fluxes, and duration of storage at different crustal levels is crucial for understanding such systems, but these parameters are poorly constrained due to the scarcity of exposed crustal sections. Here we present the first detailed reconstruction of magma emplacement and differentiation time scales of a complete crustal-scale igneous system exposed in the southern Alps (Ivrea-Sesia region, northern Italy) to quantify the magma fluxes and duration of transcrustal magmatism. Integrated zircon U-Pb petrochronology and numerical modeling provides unprecedented evidence that the volcanic and plutonic bodies are directly related to each other both chemically and temporally, suggesting that the entire magmatic system grew rapidly from its deepest roots to the erupted products. In the entire crustal section, zircons record 4 m.y. of magma accretion, but the bulk of the magma was emplaced within approximately 2 m.y. during an episode of enhanced magma flux from the mantle. Our results show the synchronous growth and differentiation of discrete magma bodies at various crustal levels beneath silicic caldera volcanoes and reconcile modeling and geochronological results on crustal-scale heat and mass transfer. [ABSTRACT FROM AUTHOR]

Abstract We combined literature and experimental data to determine the role of magma mixing in the pre-eruptive dynamics of the Aeolian Islands volcanoes. As a first step, we systematically reviewed the evidence supporting the hypothesis of mixing-triggered eruptions in the Aeolian archipelago, providing textural, chemical, and rheological constraints. The existing data highlighted the significant role of magma mixing in many eruptions within the Aeolian archipelago. Examples include the Upper Pollara and Porri volcano eruptions at Salina, Monte Guardia, and the AD 1230 Monte Pilato eruption at Lipari, as well as the present-day activity at Stromboli. Then, we focused on Vulcano Island, chosen as a case study because it represents one of the volcanoes posing the highest risk in the Aeolian archipelago. At Vulcano Island, we highlighted the role of magma mixing in the AD 1739 and 1888–90 eruptions. Finally, we investigated mixing-to-eruption timescales for the AD 1739 eruption, performing mixing experiments, and evaluated the progressive decay of the chemical concentration variance with time. Results pointed to mixing-to-eruption timescales of the order of 29 ± 9 h and magma ascent rates ranging between 3×10−2 and 5×10−2 m s−1. We finally emphasized that the presented results may have significant implications in the context of volcanic hazard mitigation and planning of emergency activities. Highlights • Magma mixing plays a key role in magmatic feeding systems of Aeolian volcanoes. • Magma mixing plays a key role in the AD 1739 eruption at Vulcano Island. • Mixing experiments are a valid proxy to constrain mixing-to-eruption timescales. [ABSTRACT FROM AUTHOR]

Abstract: At the Mount Etna volcano (Italy) the massive release of magmatic gasses (especially H2O, CO2 and SO2) during explosive eruptions and through the persistent gas plume, raises important issues: i) the volume of magma erupted at given periods is insufficient to feed the gas plume of the related periods; ii) gas-dominated, explosive eruptions do not emit differentiated products, but relatively Mg-rich magmas; iii) H2O measured in melt inclusions (~3.5wt.% at about 0.4GPa) exceeds what is expected from intraplate mantle-derived melts (<1.4wt.%). Literature data on melt inclusions (MIs) along with textural and compositional analyses of plagioclase and phase stability constrained by MELT calculations, enabled us to build a model that reconciles the abovementioned discrepancies with the high variability of the water content along the Etnean feeding system. We propose that along an open magma conduit, continuous gas loss from the free surface of magma at depth promotes an almost steady stream of H2O-rich fluid extending well below the gas saturation depth. The velocity of volatile migration might be enhanced by the huge amount of CO2 present at Mount Etna, because the CO2 exsolved at high-pressure conditions may act as carrier for other volatile species. In this way the H2O-undersaturated primitive magma present in the plumbing system, may undergo a volatile “flushing” proportional to the residing time. This process is fundamental to increase the originally low H2O content of primitive magma (≤1.4wt.%) allowing it to overcome the saturation threshold, to exsolve as gas and to promote the eruption of Mg-rich lavas. Such mechanism would also account for the unexpectedly high amount of magmatic water released during non-eruptive periods. [Copyright &y& Elsevier]

Abstract: The Permian Ora Formation (277–274Ma) preserves the products of the Ora caldera ‘super-eruption’, Northern Italy. The stratigraphic architecture of the exceptionally well preserved intra-caldera succession provides evidence for caldera collapse at the onset of the eruption, a multiple discharge point, fissure eruption style, and progressive, incremental caldera in-filling by numerous pyroclastic flow pulses within the caldera. The ignimbrites of the Ora Formation are voluminous (>1290km3), crystal-rich (~25 to 55%), and ubiquitously welded. The Ora Formation has been divided into four members (a–d), which also define the principal eruption phases. The eruption proceeded in four main stages: (1) early caldera collapse and vent opening, producing locally distributed, basal co-ignimbrite lithic breccia (member a); (2) vent clearing, which produced the eutaxitic, lithic-rich ignimbrite and minor thin ground and ash-cloud surge deposits (member b); (3) waxing and steady eruption, which produced the dominant eutaxitic, coarse-crystal-rich ignimbrite, with local lithic-rich and fine-crystal-rich ignimbrite and minor surge deposits (member c); and (4) waning eruption, recorded by the eutaxitic, fine-crystal-rich ignimbrite, with local lithic-rich ignimbrite deposits (member d). The incremental filling and late-stage outpouring of pyroclastic material from the caldera is recorded by vertical and lateral lithofacies deposit variation and some correlation between stratigraphic sections. These findings reveal a structure to the outwardly monotonous, >1300m thick, intra-caldera fill and thinner (<230m) outflow successions. These data together with the gradational contacts between the main ignimbrite lithofacies, support the hypothesis that pyroclastic material was erupted from multiple source regions in various parts of the caldera, during quasi-steady, low eruption column collapse and pyroclastic flow forming events. Field study revealed the absence of a Plinian fallout deposit, suggesting a lack of a high, buoyant, Plinian precursor eruption phase. This caldera was initiated immediately by a low collapsing column phase, producing the main, thick ignimbrite succession. Simultaneously, catastrophic volcano-tectonic caldera collapse and decompression of the magma chamber occurred, facilitated by the regional extensional environment in the Permian and pre-existing crustal weaknesses. The Ora pyroclastic flow system is suggested as having been a hot and poorly expanded, high particle concentration, granular density current. The confined nature of the majority of the erupted products to the intra-caldera setting, reduced the formation of the full array of facies commonly expected in ignimbrites in extra-caldera settings. [Copyright &y& Elsevier]

Abstract: The Green Tuff (GT) Plinian eruption, the largest in magnitude at Pantelleria, erupted 3 to 7km3 DRE of pantellerite magma and a small volume of trachyte. Fifty-nine anorthoclase-hosted melt inclusions from the two basal pumice members were analyzed by FT-IR spectroscopy in order to assess the pre-eruptive H2O content in the pantellerite melt. Microanalytical methods were used to determine major element, Cl, F and S contents. Melt inclusions and glassy groundmasses have a nearly homogeneous pantelleritic composition (peralkaline index=1.9-2.2) and variable water contents ranging from 1.4 to as high as 4.2 wt %, i.e. much higher than the 1.4 wt % of earlier published studies. The chlorine content is constant at about 1 wt %. Combined Cl and H2O data were used to estimate a confining pressure of about 50MPa (depth around 2-3km) for the GT magma chamber. The chamber was characterized by a compositional zoning with a dominant pantellerite overlying a trachyte magma. Soon after the GT eruption, intra-caldera volcanism was dominated by the eruption of voluminous trachyte lava flows, while pantellerite melt production resumed after about 20ka with numerous low-volume, mildly explosive (Strombolian) to effusive eruptions. Comparison with data from the literature reveals that, despite the different explosivity, the post-caldera Strombolian eruptions and the GT Plinian eruption were fed by pantelleritic magmas with similar water contents. Chlorine and CO2 contents suggest that the young magma reservoirs feeding the Strombolian to effusive activity were deeper (h≥4.5km) than the much larger (based on erupted volumes) magma chamber which fed the GT eruption. [Copyright &y& Elsevier]

Abstract: A deeply eroded diatreme field, consisting in several, decametric-sized, vertical, mainly clastic volcanic bodies of basaltic composition is described for the first time in the Variscan basement of SW Sardinia. The recognition and description of four different lithofacies in these diatremes allowed discussion of the role of the different processes which control magma eruption and conduit infilling, and making general inferences about diatremes. The studied diatremes have a cross-sectional shape from elliptical to sub-triangular, and are slightly elongated nearly parallel to the main foliation of the intruded meta-sedimentary rocks. Foliation of host rocks is locally reoriented or folded close to the contact with the diatremes, suggesting that magma possibly rose to the surface through fissures oriented nearly parallel to host rock foliation. Textural features of the volcanic bodies show many analogies with kimberlitic diatremes, despite the difference in petrography and composition. Juvenile lapilli are mainly made by ghosts of mafic phenocrysts (olivine and clinopyroxene) set in a groundmass formed by plagioclase microlites immersed in a cryptocrystalline, chlorite-rich matrix. The four lithofacies were described mainly based on the shape and physical features of the clasts and textural anisotropy: a globular, juvenile-rich, lapilli tuff facies (GJLt); an angular, juvenile-rich, lapilli tuff facies (AJLt); a lithic-rich, lapilli tuff facies LiRLt), and a coherent, lava-like facies (COH). All the clastic lithofacies are generally well sorted and typically lack a fine-grained matrix. Juvenile fragments are lapilli sized and from equant to oblate in axial ratio, and from rounded-globular to very angular in shape. Conversely, lithic clasts are largely variable in shape and size, and are mainly represented by basement-derived clasts. The absence of bedding, the scarcity of the coherent facies and the dominance of clast supported, structureless, volcaniclastic facies suggest that the outcropping portion of these volcanic bodies represents the lower diatreme zone. The presence of diffuse welding and the globular shapes of some juvenile fragments, together with their vesicularity, suggest that magma fragmentation was mainly driven by magmatic gas exsolution occurring at a deeper level respect to classical, basaltic explosive activity. Textural features, facies association and facies architecture of the studied deposits are suggestive of an important affinity with kimberlitic and other ultramafic diatremes. [Copyright &y& Elsevier]

We investigated the eruptive episodes that occurred at Etna volcano on 15 November 2011 and 18 March 2012 using different types of data. We present novel data from two recently installed strainmeters that recorded unique signals during the lava fountain phases of these events. The strainmeter data, integrated with those recorded by the magnetic network, and with satellite and ground thermal data, allowed us to follow the path of a gas-rich magma batch from the source inside the volcano to the surface and atmosphere. The amplitude ratio of the volumetric strain changes constrained the storage depth of the magma feeding the lava fountains above 1.5 km below sea level. Magnetic data revealed an attempted shallow lateral intrusion, whereas ground and satellite thermal data furnished a quantification of the total erupted volumes of ∼2.2 × 10 m for the 15 November event and ∼3.0 × 10 m for the 18 March event. Despite different durations of the explosive and effusive phases of the two lava fountain events, the total erupted volume was quite similar, suggesting the emptying of a shallow storage system displaying a steady behaviour. [ABSTRACT FROM AUTHOR]

One of the major objectives of volcanology remains relating variations in surface monitoring signals to the magmatic processes at depth that cause these variations. We present a method that enables compositional and temporal information stored in zoning of minerals (olivine in this case) to be linked to observations of real-time degassing data. The integrated record may reveal details of the dynamics of gradual evolution of a plumbing system during eruption. We illustrate our approach using the 2006 summit eruptive episodes of Mt. Etna. We find that the history tracked by olivine crystals, and hence, most likely the magma pathways within the shallow plumbing system of Mt. Etna, differed considerably between the July and October eruptions. The compositional and temporal record preserved in the olivine zoning patterns reveal two mafic recharge events within months of each other (June and September 2006), and each of these magma supplies may have triggered the initiation of different eruptive cycles (July 14-24 and August 31-December 14). Correlation of these observations with gas monitoring data shows that the systematic rise of the CO/SO gas values is associated with the gradual (pre- and syn-eruptive) supply of batches of gas-rich mafic magma into segments of Etna's shallow plumbing system, where mixing with pre-existing and more evolved magma occurred. [ABSTRACT FROM AUTHOR]

Vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions. Although their numbers and sizes are used routinely to infer aspects of eruption dynamics, vesicle shape remains an underutilized parameter. We have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles, using the dimensionless shape factor $\Omega $, a measure of the degree of complexity of the bounding surface of an object. For each of the seven eruptions, we have also estimated the capillary number, Ca, from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling. We find that $\Omega $ is smaller for eruptions with ${\rm{Ca}} \ll 1$ than for eruptions with Ca $\gg 1$. Consistent with previous studies, we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth, such as coalescence and shape relaxation of bubbles by capillary stresses. Among the samples analyzed, Strombolian and Hawaiian fire-fountain eruptions have ${\rm{Ca}} \ll 1$, in contrast to Vulcanian, Plinian, and ultraplinian eruptions. Interestingly, the basaltic Plinian eruptions of Tarawera volcano, New Zealand in 1886 and Mt. Etna, Italy in 122 BC, for which the cause of intense explosive activity has been controversial, are also characterized by ${\rm{Ca}} \gg 1$ and larger values of $\Omega $ than Strombolian and Hawaiian style (fire fountain) eruptions. We interpret this to be the consequence of syn-eruptive magma crystallization, resulting in high magma viscosity and reduced rates of bubble growth. Our model results indicate that during these basaltic Plinian eruptions, buildup of bubble overpressure resulted in brittle magma fragmentation. [ABSTRACT FROM AUTHOR]

Abstract: Volcanic CO2 degassing is considered the primary process that controls the global carbon cycle over geological timescales. However, fluxes of CO2 from individual volcanoes, in particular those in past activities, have been poorly constrained. One way to estimate the flux is by using the H2OCO2 systematics of melt inclusions, which, according to petrological studies, records fluxing of a deep-derived CO2-rich fluid in the deep to shallow-level crustal magmatic systems. Assuming that this fluid fluxing is the process of volcanic CO2 emission, we quantified the fluxes of CO2 by combining a fluid transport model with melt inclusion data. We formulated CO2 fluxing as an advective fluid flow in a basaltic magma column with exchanging volatiles, and applied it to the melt inclusion data from Mount Etna, the type locality of a CO2-emitting volcano. The flux of CO2 was calculated to be 2.4–6.0kt/day, which is consistent with the observed volcanic CO2 emission rate of 1–10kt/day. We propose that this method potentially provides a means to quantify CO2 emission rates in past volcanic activities. Because CO2 fluxing is an open-system process, the estimated CO2 emission over geological timescales evaluated with this method should give much higher values than evaluations based simply on the volume of the erupted magmas. [Copyright &y& Elsevier]

Abstract: The 15 March, 2007 Vulcanian paroxysm at Stromboli volcano was recorded by several instruments that allowed description of the eruptive sequence and unraveling the processes in the upper feeding system. Among the devices installed on the island, two borehole strainmeters recorded unique signals not fully explored before. Here we present an analysis of these signals together with the time-lapse images from a monitoring system comprising both infrared and visual cameras. The two strainmeter signals display an initial phase of pressure growth in the feeding system lasting ∼2min. This is followed by 25s of low-amplitude oscillations of the two signals, that we interpret as a strong step-like overpressure building up in the uppermost conduit by the gas-rich magma accumulating below a thick pile of rock produced by crater rim collapses. This overpressure caused shaking of the ground, and triggered a number of small landslides of the inner crater rim recorded by the monitoring cameras. When the plug obstructing the crater was removed by the initial Vulcanian blast, the two strainmeter signals showed opposite sign, compatible with a depressurizing source at ∼1.5km depth, at the junction between the intermediate and shallow feeding system inferred by previous studies. The sudden depressurization accompanying the Vulcanian blast caused an oscillation of the source composed by three cycles of about 20s each with a decreasing amplitude, as well recorded by the strainmeters. The visible effect of this behavior was the initial Vulcanian blast and a 2–3km high eruptive column followed by two lava fountainings displaying decreasing intensity and height. To our knowledge, this is the first time that such a behavior was observed on an open conduit volcano. [Copyright &y& Elsevier]

Abstract: The Villa Senni Formation (355ka) represents the youngest mafic caldera-forming eruption of the Colli Albani Volcano (Central Italy), and one of the best exposed large mafic ignimbrite successions on Earth. The unusual Si-undersaturated and high-K composition of the magma, and corresponding low magma viscosity, raise important questions about the conditions of magma ascent, eruption, and fragmentation that led to such a large explosive eruption. We examined the juvenile clast textures – that is, the abundance, shape, size and number density of both vesicles and leucite microlites – to reconstruct the fragmentation conditions and to trace major changes in the ascent rate and vesiculation history of the magma associated with caldera collapse. The juvenile textures record two major changes in the eruption dynamics through the stratigraphy. First, the sudden depressurization of the magma chamber and the onset of the first ignimbrite-forming phase are marked by a dramatic increase in the magma ascent velocity inferred by a decrease in vesicle and leucite microlite sizes and increase in their number densities. Second, the progressive restoration of pressure within the magma reservoir as a consequence of caldera collapse is recorded by an inversion of vesicle and leucite microlite textures, which suggest a strong decrease in magma ascent rate. Complex vent conditions in this later phase of the caldera collapse are recorded by the diversity of textural features, variation in magma chemistry and the abrupt changes in the stratigraphic record (including the presence of co-ignimbrite breccias, spatter clasts and lithics). [Copyright &y& Elsevier]

The 3.7 ka year-old Averno 2 eruption is one of the rare eruptions to have occurred in the northwest sector of the Phlegraean Fields caldera (PFc) over the past 5 ka. We focus here on the fallout deposits of the pyroclastic succession emplaced during this eruption. We present major and trace element data on the bulk pumices, along with major and volatile element data on clinopyroxene-hosted melt inclusions, in order to assess the conditions of storage, ascent, and eruption of the feeding trachytic magma. Crystal fractionation accounts for the evolution from trachyte to alkali-trachyte magmas; these were intimately mingled (at the micrometer scale) during the climactic phase of the eruption. The Averno 2 alkali trachyte represents one of the most evolved magmas erupted within the Phlegraean Fields area and belongs to the series of differentiated trachytic magmas erupted at different locations 5 ka ago. Melt inclusions record significant variations in HO (from 0.4 to 5 wt%), S (from 0.01 to 0.06 wt%), Cl (from 0.75 up to 1 wt%), and F (from 0.20 to >0.50 wt%) during both magma crystallization and degassing. Unlike the eruptions occurring in the central part of the PFc, deep-derived input(s) of gas and/or magma are not required to explain the composition of melt inclusions and the mineralogy of Averno 2 pumices. Compositional data on bulk pumices, glassy matrices, and melt inclusions suggest that the Averno 2 eruption mainly resulted from successive extrusions of independent magma batches probably emplaced at depths of 2-4 km along regional fractures bordering the Neapolitan Yellow Tuff caldera. [ABSTRACT FROM AUTHOR]

Abstract: The eruptive history of Mt. Somma–Vesuvius is characterised by large explosive events: Pomici di Base eruption (22,030±175yrcal BP), Mercato (8890±90yrcal BP), Avellino (3945±10yrcal BP) and Pompeii (79AD). Pre-eruptive conditions and sin-eruptive degassing processes of the Avellino eruption, the highest-magnitude Plinian event, have been investigated, using volatile contents (F, Cl, H2O) in melt inclusions and residual glass, and textural characteristics of pumice clasts of the 9 fallout layers sampled in detail in a representative sequence. The sequence displays an up-section sharp colour change from white to grey, corresponding to variations in both magma composition and textural characteristics. The pre-eruptive conditions have been constrained by systematic measurements of Cl content in both melt inclusions and matrix glass of pumice clasts. The pumice glass composition varies from Na-rich phonolite (white pumice) to K-rich phonolite (grey pumice). The measured Cl values constantly cluster at 5200±400ppm (buffer value), whatever the composition of the melt, suggesting that the entire magma body was saturated with sub-critical fluids. This Cl saturation constrains the pre-eruptive pressures and maximum H2O contents at 200±10MPa and 6.3±0.2wt.% H2O for the white pumice melt and 195±15MPa and 5.2±0.2wt.% H2O for the grey pumice melt. The fluid phase, mainly composed of a H2O-rich vapour phase and brine, probably accumulated at the top of the reservoir and generated an overpressure able to trigger the onset of the eruption. Magma degassing was rather homogeneous for the white and grey eruptive units, mostly occurring through closed-system processes, leading to a typical Plinian eruptive style. A steady-state withdrawal of an H2O-saturated magma may explain the establishment of a sustained Plinian column. Variation from white to grey pumice is accompanied by decrease of mean vesicularity and increase of mean microcrystallinity and permeability related to significant vesicle coalescence. Despite this, the ascending magma column still evolves under closed-system degassing, without significant gas loss through conduit walls. The Avellino eruption shows numerous similarities with the 79AD Pompeii eruption in pre-eruptive conditions, degassing processes and eruptive style which are discussed here. [Copyright &y& Elsevier]

Abstract: Volcanic rock samples were systematically collected during the 2006 eruptive episodes at Mt. Etna. Major and trace elements, together with Sr–Pb isotope ratios, were then obtained on the whole rocks, for different times of emission and vent locations. On the same samples, selected plagioclase crystals were investigated through high-contrast BSE images and core-to-rim compositional profiles for An% and FeO wt.% were obtained. The major element variation through time suggests the involvement of a more basic magma, because MgO/FeOtot and CaO/Al2O3 ratios tend to increase from the beginning to the end of the eruption. This more basic magma was characterized by a peculiar geochemical and isotopic signature. This is testified by the negative trend of LREEs, some HFSEs (e.g., Nb, Zr, Y) and lead isotopes, together with increase of some incompatible element ratios (e.g., Rb/La, Zr/Nb) with respect to products erupted before. Concerning the plagioclase crystals, four main texture types were recognized at the core and rim, which indicate either near-equilibrium crystallization or disequilibrium accompanied by strong destabilization. These textures were attributed to: i) crystallization at equilibrium conditions at depth or within the open-conduit (two types of oscillatory zoning), ii) magma decompression at variable ascent rates (coarsely sieve-textures and dissolution at the core), iii) inputs of more basic magma (sieve-textured rims). All the available data, coupled with CO2/SO2 molar ratio measured in the gas plume obtained from literature, support the idea that the pulsating regime observed for the volcanic phenomena at the surface during the period July–December 2006 reflects the transient, rapid ascent of several CO2 bubble fluxes and/or CO2-rich magma batches from the deep to the shallow levels of the plumbing system. This integrated study has also led to the identification of the replenishment event during the eruption that allowed the ingress of the magma with distinct geochemical/isotopic signature. [Copyright &y& Elsevier]

Between 1989 and 2001, five eruptions at Etna displayed a regular alternation between repose periods and episodes rich in gas, termed quasi-fire fountains and consisting of a series of Strombolian explosions sometimes leading to a fire fountain. This behaviour results from the coalescence of a foam layer trapped at the top of the reservoir which was periodically rebuilt prior to each episode (Vergniolle and Jaupart, J Geophys Res 95:2793-2809, ). Visual observations of fire fountains are combined with the foam dynamics to estimate the five degassing parameters characteristic of the degassing reservoir, i.e. the number of bubbles, gas volume fraction, bubble diameter, reservoir thickness and reservoir volume. The study of decadal cycles of eruptive patterns (Allard et al., Earth Sci Rev 78:85-114, ) suggests that the first eruption with fire fountains occurred in 1995 while the last one happened in 2001. The number of bubbles and the gas volume fraction increase smoothly from the beginning of the cycle (1995) to its end (2001). The increasing number of bubbles per cubic metre, from 0.61-20×10 to 0.1-3.4×10, results from cooling of the magma within the reservoir. The simultaneously decreasing bubble diameter, from 0.67-0.43 to 0.30-0.19 mm, is related to the decreasing amount of dissolved volatiles. Meanwhile, the thickness and the volume of the degassing reservoir diminish, from values typical of the magma reservoir to values characteristic of a very thin bubbly layer, marking the quasi-exhaustion of volatiles. The magma reservoir has a slender vertical shape, with a maximum thickness of 3,300-8,200 m and a radius of 240 m (Vergniolle ), making its detection from seismic studies difficult. Its volume, at most 0.58-1.4 km, is in agreement with geochemical studies (0.5 km) (Le Cloarec and Pennisi, J Volcanol Geotherm Res 108:141-155, ). The time evolution of both the total gas volume expelled per eruption, and the inter-eruptive gas flux results from the competition between the increasing number of bubbles and the decreasing bubble diameter. The smooth temporal evolution of the five degassing parameters also points towards bubbles being produced by a self-induced mechanism within the magma reservoir rather than by a magmatic reinjection prior to each eruption. The decadal cycles are therefore initiated by a magmatic reinjection, in agreement with a typical return time of 14-80 years (Albarède ). Hence, the 1995 eruption results from a fresh magma being newly emplaced while the magma from the following eruptions is progressively depleted in volatiles species until reaching a state of quasi-exhaustion in 2001. A magmatic reinjection of 0.13-0.6 km every few decades is sufficient to explain the expelled gas volume, including SO. A scenario is also proposed for the alternation between gas-rich summit eruptions and gas-poor flank eruptions which are observed during decadal cycles. The scenario proposed for Etna could also be at work at Piton de la Fournaise and Erta 'Ale volcanoes. [ABSTRACT FROM AUTHOR]

Decompression experiments have been conducted to simulate syn-eruptive crystallization in volcanic conduits, to infer magma ascent rates and conditions during dome-forming and Plinian eruptions of silicic arc volcanoes. The experiments were carried out on starting material with the composition of Mt. Pelée rhyolitic interstitial melt (76 wt % SiO2) and consisted of three consecutive steps: hydration, decompression, and annealing. Hydration (saturated and undersaturated) was performed at 850°C and 200 MPa and was followed by isothermal decompression, either linearly or stepwise, to a final pressure, Pf, of 30 or 5–10 MPa. Decompression rates range from 0·003 to 25 MPa min−1 (decompression durations of 15 min to 40 days). Two samples were cooled by 25°C and 50°C during a 3 day step at Pf. Subsequent to decompression, the samples were held for up to 15 days at Pf. The experiments generated three types of crystals as products of pre-, syn-, and post-decompression crystallization. The experiments basically differ from previous studies in that they are specifically designed to discriminate crystal nucleation from growth and to evaluate the influence of pre-decompression crystals on the decompression-induced crystallization. The effects of pre-decompression crystals, decompression rate, undercooling (Pf), and terminal cooling have been determined on plagioclase nucleation, growth, morphology, and composition. The main results suggest a positive correlation between decompression rate and the number density of plagioclase crystals nucleated at Pf and highlight the effect of pre-decompression crystals in further decompression-induced crystallization. The relations between the decompression conditions and the plagioclase characteristics have been used to infer Mt. Pelée eruption dynamics, suggesting that (1) Plinian magmas ascend from the reservoir within less than 1 h (1–10 m s−1), (2) dome and block-and-ash flow magmas ascend within more than 2–5 days, giving time for syn-decompression crystallization around pre-existent microlites, (3) dome magmas provide evidence for long stagnation and cooling at low pressure, and (4) surge magmas ascend without significant crystallization (within less than ∼4 days) and massively nucleate plagioclase at very low pressure. The extent and violence of dome destruction may depend on the size or age of the dome, with large or old domes favouring mildly explosive block-and-ash flows, whereas small or young protodomes may generate highly explosive surges. [ABSTRACT FROM PUBLISHER]

Mount Etna volcano (Italy) during the period 2001-2005 has undergone a period of intense eruptive activity marked by three large eruptions (2001, 2002-2003 and 2004-2005). These eruptions encompassed diverse eruptive styles and regimes: from intensely explosive, during 2001 and 2002-2003 eruptions, to exclusively effusive in the 2004-2005 event. In this work, we put forward the idea that these three eruptions are the response of the progressive arrival into the uppermost segment of the open-conduit system of a new magma, which was geochemically distinct in terms of trace element and Sr-Nd-Pb isotope signature from the products previously emitted by the Etnean volcano. The magma migrated upwards mainly through a peripheral tectonic system, which can be considered as eccentric in spite of its relative proximity to the main system. The ingress of the new magma and its gradual displacement from the eccentric system into the uppermost sector of the open-conduit gave rise to different eruptive behaviours. At the beginning, the ascent of the undegassed magma, able to exsolve a gas phase at depth, and its interaction with closed-system magma reservoirs less than 10 km deep gave rise to the explosive events of 2001 and 2002-2003. Later, when the same magma entered into the open-conduit system, it took part in the steady-state degassing and partially lost its volatile load, leading to a totally effusive eruption during the 2004-2005 event. One further consideration highlighted here is that in 2001-2005, migration of the feeding axis from an eccentric and peripheral position towards the main open-conduit has led to the development of a new vent (South East Crater 2) located at the eastern base of the South East Crater through which most of the subsequent Etnean activity occurred. [ABSTRACT FROM AUTHOR]

Abstract: Twelve years of night-time MODIS (Moderate Resolution Imaging Spectroradiometer) observations, has been analysed to detect and quantify the radiative heat power emitted by Stromboli volcano (from March 2000 to September 2011). Using an accurate background subtraction of the MODIS signal at 4μm, we were able to discriminate two main regimes of thermal radiation, related to different levels of volcanic activity. Effusive eruptions (occurred on December 28, 2002 and February 27, 2007) radiated at an average of ~186MW with a frequency of alert detection of 50–95%. Conversely, during the typical strombolian activity, an average of ~9MW is radiated, with a frequency of alert detection of 0–45%. Although during the effusive eruptions the radiative power is basically controlled by the lava discharge rate, our results suggest that during non-effusive periods (strombolian regime) both the intensity and the frequency of MODIS alerts are controlled by the height of the magmatic column feeding the activity at the surface. In particular we found that a radiative power of ~50MW corresponds to a high magma column which is exposed, in the vent area, at the same rate in which the deeper gas-rich magma is typically supplied within the feeding system of Stromboli (~0.3m3 s−1). In this condition the magmatic system approaches steady state regimes. Above this threshold a transition from strombolian to effusive regimes may occur as shown by the detection of ~50MW, 8–10days before the onset of both the last two major flank eruptions. These values were reached after 1–2months of gradual increase of the radiative power which was likely associated the rising of the magma column within the shallowest portion of the conduit. In addition our data suggest that over the years 2000–2011 several cycles of rise and fall of the magma column have occurred, which however did not culminate into an effusive eruption but only into recurrent episodes of sustained spattering or fountaining and summit overflows. These fluctuations has substantially increased in frequency and intensity after the 2007 eruption thus suggesting that this event has perturbed in some way the shallow plumbing system of Stromboli. We stress that the detection of a radiative power higher than 50MW is a clear evidence of a very high magma column, which may prelude the onset of an effusive eruption and/or periods of sustained vent activity. In conclusion, we suggest that systematic analysis of MODIS data can be used to detect variations in the intensity of strombolian activity and may considerably improve volcano surveillance at Stromboli, as well as at other open-system volcanoes. [Copyright &y& Elsevier]

Recent stratigraphic studies at Vesuvius have revealed that, during the past 4,000 years, long lasting, moderate to low-intensity eruptions, associated with continuous or pulsating ash emission, have repeatedly occurred. The present work focuses on the AS1a eruption, the first of a series of ash-dominated explosive episodes which characterized the period between the two Subplinian eruptions of 472 AD and 1631 AD. The deposits of this eruption consist of an alternation of massive and thinly laminated ash layers and minor well sorted lapilli beds, reflecting the pulsatory injection into the atmosphere of variably concentrated ash-plumes alternating with Violent Strombolian stages. Despite its nearly constant chemical composition, the juvenile material shows variable external clast morphologies and groundmass textures, reflecting the fragmentation of a magma body with lateral and/or vertical gradients in both vesicularity and crystal content. Glass compositions and mineralogical assemblages indicate that the eruption was fed by rather homogeneous phonotephritic magma batches rising from a reservoir located at ~ 4 km (100 MPa) depth, with fluctuations between magma delivery and magma discharge. Using crystal size distribution (CSD) analyses of plagioclase and leucite microlites, we estimate that the transit time of the magma in the conduit was on the order of ~ 2 days, corresponding to an ascent rate of around 2 × 10 ms. Accordingly, assuming a typical conduit diameter for this type of eruption, the minimum duration of the AS1a event is between about 1.5 and 6 years. Magma fragmentation occurred in an inertially driven regime that, in a magma with low viscosity and surface tension, can act also under conditions of slow ascent. [ABSTRACT FROM AUTHOR]

Abstract: Our ability to monitor volcanoes (using seismic signals, ground deformation, gas fluxes, or other ground and satellite based observations) as well as our understanding of melt reservoirs that feed eruptions have evolved tremendously in recent years. The complex plumbing systems that are thought to feed eruptions are, however, difficult to relate to the monitoring signals. Here we show that the record preserved in compositional zoning of erupted minerals may be used to reconstruct sections of the plumbing system. Kinetic modeling of such zoning can yield information on the residence time of magma in different segments of the plumbing systems. This allows a more nuanced evaluation of the link between observed monitoring signals or eruption styles and the magmatic processes and movement of batches of melts at depth. The approach is illustrated through a study of the compositional zoning recorded in olivine crystals from the 1991–1993 SE-flank eruption products of Mt. Etna (Sicily). The zoning patterns in crystals reveal that the plumbing system of the volcano consisted of at least three different magmatic environments between which magma was transported and mixed in the year or two preceding the start of eruption. Quantification of this history indicates that two main pathways of melt migration and three timescales dominated the dynamics of the system. Combination of this information with the timing of observation of various monitoring signals allows a reconstruction of the dynamic evolution of this section of the plumbing system during the early stages of the 1991–1993 eruption. It is seen, for example, how the migration of melt through the same sections of the plumbing system can cause pre-eruptive triggering, enhance Strombolian activity, and through the ensuing eruption cleanse and flush the plumbing system. Different kinds of mixing occur simultaneously at different sections of the plumbing system on different timescales (a few days up to two years). [Copyright &y& Elsevier]

Abstract: Using Etna as a case study location, we examine the balance between the volume of magma supplied to the shallow volcanic system (using ground-based SO2 data) and the volume erupted (using satellite thermal data). We do this for three eruptions of Mt. Etna (Italy) during 2002 to 2006. We find that, during the three eruptions, 2.3×107 m3 or 24% of the degassed volume remained unerupted. However, variations in the degree of partitioning between supplied (Vsupply) and erupted (Verupt) magma occur within individual eruptions over the time scales of days. Consequently, we define and quantify three types of partitioning. In the first case, Vsupply Verupt, i.e. less lava is erupted than is supplied. In such a case, magma can erupt in an explosive manner, as occurred during Phase II of the 2002–2003 eruption, or remain within or below the edifice. In the third case, Vsupply =Verupt, i.e. all supplied magma is erupted. During 2002–2006, over a total of 280days of eruptive activity, this balancing case applied to 50% of the time. [Copyright &y& Elsevier]

Abstract: Our ability to forecast volcanic hazards at active volcanoes stems from our knowledge of parameters affecting eruption dynamics. Persistent activity displayed by basaltic volcanic systems, such as Etna and Stromboli, is governed mainly by the textural evolution and rheological properties of eruptive products. Here, we investigate the high temperature (1131°C< T <1187°C) rheological behavior and textural evolution of remelted natural basaltic magmas from Stromboli and Etna volcanic systems upon cooling and crystallization at atmospheric conditions. The pure liquid and subliquidus isothermal viscosities are investigated using a concentric cylinder apparatus by varying strain rate applied to the investigated materials. Detailed textural analysis has been performed in order to evaluate the effect of crystal distribution on the rheological evolution of magmas. At subliquidus conditions, the mineralogical assemblage is dominated by the presence of spinel and plagioclase with the occurrence of stable clinopyroxene only at the lowest temperatures (1157 and 1131°C for the Stromboli and the Etna samples, respectively). The overall crystal fraction (ϕ) varies between 0.06 and 0.27. In the high T regime the viscous response to applied stress and strain rate is strongly affected by the presence of even small amounts of crystals. Large discrepancies between measured and predicted viscosities obtained using the Einstein–Roscoe (ER) equation are also found at low crystal fractions. We find here that, at the investigated conditions, the physical effect caused by the presence of elongated crystals is orders of magnitude higher than that predicted by existing models which only account for spherical particles. It also appears that a weak shear thinning behavior occurs at the lowest temperatures investigated. Crystal shape and, with it, the strain-rate dependence of the rheological properties appear to play primary roles in influencing the transport properties of these basaltic magmas. [Copyright &y& Elsevier]

The article discusses the evidence for the carbon dioxide (CO2)-driven origin of the explosion of Stromboli volcano in Italy. It states that the explosions are systematically preceded by a brief phase of increasing CO2/ S02 weight ration. It cites that non-linear magma flow could account to the observed C02 degassing patterns. It also mentions that C02-rich gas triggers demonstrates possibility to forecast explosions.

Abstract: The extent of fragmentation triggered by basaltic volcanic eruptions has been studied by analyzing the grain size distribution of natural pyroclastic deposits and applying the fractal fragmentation theory. For this purpose, 75 samples have been collected from individual layers along horizontal section of the well-exposed Valentano scoria cone (Italy). The cone is constituted by well-defined layers of fall deposits of up to 180cm in thickness. An important feature of the stratigraphic sequence is the occurrence of several intercalated layers (called breccias) with clasts of different characteristics (angular shape, low porosity, and high crystallinity) in respect to the “normal layers”. Results indicate that all achieved grain size distributions show fractal behavior and can be clearly correlated with a single fragmentation event, namely the magmatic fragmentation during the eruption. The fractal dimension of fragmentation (D) increases as fragmentation efficiency increases. Values of D are found to vary significantly along the pyroclastic sequence defining two major trends: (1) a general, long-range increase of D during the course of the eruption and (2) a superimposed high-frequency oscillating variation of fragmentation efficiency. Noteworthy is the fact that the highest values of D are measured for pyroclastic deposits following breccia deposits. Application of a conceptual model of fractal fragmentation, as claimed by natural data, indicates that larger values of D have to be associated with a higher probability of fragmentation, thus suggesting that the D value can be used as a proxy for the “fragility” (i.e. ability to fragment) of samples. Fractal dimension of fragmentation of single layers is positively correlated with the vesicularity of clasts. This indicates that the bubble content in the ascending magma prior to and at fragmentation likely was the key factor modulating the variable fragmentation efficiency observed in the studied pyroclastic sequence. We hypothesize that the long-range variation of D may be associated with magma fragmentation triggered by expansion of gas bubbles progressively coalescing below solid plugs during later stages of eruptive activity, whereas high-frequency variations of D are interpreted as due to magma fragmentation during the “slug flow” regime characterizing the strombolian activity of the scoria cone. [Copyright &y& Elsevier]

Abstract: The detailed analysis of stratigraphy allowed the reconstruction of the complex volcanic history of La Fossa di Vulcano. An eruptive activity mainly driven by superficial phreatomagmatic explosions emerged. A statistical analysis of the pyroclastic Successions led to the identification of dilute pyroclastic density currents (base surges) as the most recurrent events, followed by fallout of dense ballistic blocks. The scale of events is related to the amount of magma involved in each explosion. Events involving about 1millioncm3 of magma occurred during recent eruptions. They led to the formation of hundreds of meters thick dilute pyroclastic density currents, moving down the volcano slope at velocities exceeding 50m/s. The dispersion of density currents affected the whole Vulcano Porto area, the Vulcanello area. They also overrode the Fossa Caldera''s rim, spreading over the Piano area. For the aim of hazard assessment, deposits from La Fossa Cone and La Fossa Caldera were studied in detail, to depict the eruptive scenarios at short-term and at long-term. By means of physical models that make use of deposit particle features, the impact parameters have been calculated. They are dynamic pressure and particle volumetric concentration of density currents, and impact energy of ballistic blocks. A quantitative hazard map, based on these impact parameters, is presented. It could be useful for territory planning and for the calculation of the expected damage. [Copyright &y& Elsevier]

The 79 ad Plinian eruption of Vesuvius produced first a white pumice fallout from a high steady eruptive column, and then a grey pumice fallout originating from an oscillatory eruptive column with several partial column collapse events after which there was a total column collapse. This first total collapse was followed by renewed Plinian activity and produced the last grey pumice (GP) fallout deposit of the eruption. Textural characteristics (vesicularity and microcrystallinity) of a complete sequence of the pumice fallout deposits are presented along with the major element compositions and residual volatile contents (HO, Cl) to constrain the degassing processes and the eruptive dynamics. Large variations in residual volatile contents exist between the different eruptive units. Textural features also strongly differ between white and grey pumices, but also within the grey pumices. The degassing processes were thus highly heterogeneous. We propose a new model of the 79 ad eruption in which pre-eruptive conditions (HO saturation, magma temperature and viscosity) are the critical controls on the diversity of the syn-eruptive degassing processes and hence the eruptive dynamics. Cl contents measured in melt inclusions show that only the white pumice and the upper part of the grey pumice magma were HO saturated prior to eruption. The white pumice eruptive units represent a typical closed-system degassing evolution, whereas the first grey pumice one, stored under similar pre-eruptive saturation conditions, follows a particular open-system degassing evolution. We suggest that the oscillatory regime that dominated the grey pumice eruptive phase is linked to pre-eruptive water undersaturation of most of the grey magma, and the associated time delays necessary for HO exsolution. We also suggest that the high residual HO content of the last grey pumice, deposited after the renewal of Plinian activity following the first total column collapse event, is due to syn-eruptive saturation of GP magma and reduced HO exsolution efficiency resulting from speciation of dissolved HO in the melt. [ABSTRACT FROM AUTHOR]

Abstract: A long recharging period characterized Mount Etna volcano during 1993–2000 before the main explosive–effusive 2001 and 2002–2003 flank eruptions. The joint analysis of ground deformation and gravity data over the recharge period reveals that different phenomena occurred within Etna''s plumbing system and clearly indicates two phases spanning 1993–1997 and 1997–2000, respectively. The first phase was characterized by magma storage and accumulation at an intermediate depth (2–6km below sea level), which provoked overall inflation and positive gravity changes. During the second phase, the magma started to rise and intrude at shallower levels favoring the movement of the unstable eastern flank, which accelerated its sliding toward the East. The shallower magma accumulation also caused the gas exsolution, associated with increasing explosive activity at the summit craters. Negative gravity changes were detected during this phase. The gravity measurements, independent of the same result obtained by geochemical studies, suggest that only 20–30% of the magma volumes supplied in the plumbing system were then erupted. The complex dynamics of rising magma beneath Mount Etna makes ground deformation and gravity measurements complementary, being able to detect different effects of magma emplacements beneath the surface. Our results also highlight how the joint use of ground deformation and gravity observations may be crucial in identifying the nature and rate of an impending period of volcanic eruptions. [Copyright &y& Elsevier]

Abstract: Fluid inclusions hosted in sanidine from xenoliths, representing the crystallization front of the AD 79 magma chamber of Vesuvius, offer a rare opportunity to track the composition of magmatic fluids exsolving at the peripheral part of a growing K-alkaline magma chamber disrupted by an explosive eruption. This work demonstrates that the exsolving magmatic fluids have a complex composition taking in evidence the great capability of metal transport by means of these solutions. Inclusions are particularly enriched in Zn, Mo, W, Sb, Bi, Tl and Pb. Metals display two different positive correlations: 1) Pb–Zn–Tl–Bi; 2) Mo–W. The different trends may reflect the different complexing agent for these elements (probably chloride for Pb–Zn–Tl–Bi and probably hydroxy for Mo–W). The occurrence of a “silicothermal” component in these fluids may furthermore favor the metal transport of these solutions. This is probably a major, previously underestimated process in the enrichment of some metals in magmatic–hydrothermal systems. This hypothesis may challenge conventional ideas on fluid-phase mass transport of components by means of magmatic–hydrothermal fluids, and should be taken into account in future works on these topics. [Copyright &y& Elsevier]

Abstract: The 2007 effusive eruption of Stromboli followed a similar pattern to the previous 2002–2003 episode. In both cases, magma ascent led to breaching of the uppermost part of the conduit forming an eruptive fissure that discharged lava down the Sciara del Fuoco depression. Both eruptions also displayed a ‘paroxysmal’ explosive event during lava flow output. From daily effusion rate measurements retrieved from helicopter- and satellite-based infrared imaging, we deduce that the cumulative volume of lava erupted before each of the two paroxysms was similar. Based on this finding, we propose a conceptual model to explain why both paroxysms occurred after this ‘threshold’ cumulative volume of magma was erupted. The gradual decompression of the deep plumbing system induced by magma withdrawal and eruption, drew deeper volatile-rich magma into the conduit, leading to the paroxysms. The proposed model might provide a basis for forecasting paroxysmal explosions during future effusive eruptions of Stromboli. [Copyright &y& Elsevier]

Abstract: Stromboli is considered one of the most active volcanoes in the world, and its persistent but moderate explosive activity is only interrupted by occasional episodes of more vigorous activity accompanied by lava flows. A new effusive eruption began in late February 2007 and was characterized by intense seismic activity throughout the whole period. The accurate seismic signals analysis showed the presence of families of events with similar waveform signatures (i.e., multiplets) located beneath the crater region. Since traditional location techniques do not allow obtaining reliable hypocenters, our analysis focused on high precision locations of the seismicity in order to better define the source geometry of the events. Hypocenters, therefore, have been relocated considering two steps: the first, based on a robust probabilistic approach, is used to find the absolute position of the clusters and the second exploits a master-event concept for the relative location of the events. Finally, the shape of the clusters and the temporal migration of the foci were correlated with the eruptive phases. The results show that the occurrence of a cluster of events is related to the opening and closure of a vent opened in the Sciara del Fuoco slope and, in particular, to the intrusion of a dike injected by central conduit in a radial direction, whereas another cluster lies in a narrow vertical volume positioned under the crater area. The geometry of the clusters suggests a source region depicting the shallower feeding system. Overall, the results highlight that the high precision locations method is an efficient and quick tool to obtain a better understanding of the magmatic processes occurring during an ongoing eruption. [ABSTRACT FROM AUTHOR]

new multidisciplinary study, combining geology, petrography, and geochemistry, on the rocks of the isolated hill of Mount Calanna (Mount Etna, Italy) has provided evidence for the existence of a dyke swarm, formed by more than 200 dykes distributed over an area of ~0.7 km, with an intensity of intrusion up to 40%. All bodies are deeply altered, and the geological and mesostructural surveying of 132 dykes revealed that they intruded in E-W direction, with an average dip of 60°. The faults affecting the outcrop have in general an E-W strike and dip of ~55°: these have all normal motion and have been interpreted as coeval with the dykes. This interpretation contrasts with the previous hypothesis that considered Mount Calanna as a thrust resulting from compressive deformation resulting from the gravitational spreading of the volcanic edifice. Mount Calanna is here interpreted as the uppermost portion of a vertically extensive magmatic plexus that fed the eruptive activity of one (or more) eruptive center/s sited in the Valle del Bove area. Measurements of the apparent densities on 23 dykes and host rock samples give an average value of 2,420 kg/m for the entire complex, ~15% lower than the density expected for hawaiitic magma, placing an important constraint on the geophysical identification of similar structures. Considering that Mount Etna is not an old eroded edifice but an active and growing volcano, the exposure of this subvolcanic structure can be regarded as exceptional. Its geometry and physical characteristics can be thus regarded as an interesting example of the present-day shallow plumbing system of Mount Etna as well as of other basaltic volcanoes. [ABSTRACT FROM AUTHOR]

Over the last 2 years, the south east crater (SEC) at Mt. Etna (Italy) has been characterised by the intermittent emission of lava flows, often accompanied by paroxysmal episodes with violent strombolian activity and/or lava fountains. One of the most intense and intriguing episodes occurred on November 16, 2006 during strombolian and effusive activity from the very top of the SEC. At the eastern base of the crater, a violent and short-lasting outburst generated a 300-m-high eruptive curtain of finely fragmented magma and steam, which collapsed in a few seconds giving rise to a small but significant pyroclastic flow. The paroxysm was preceded by progressive sliding of the eastern flank of the SEC edifice, which led to the formation of a large niche. Previously published models explain the outburst as due to rapid vaporisation of water contained in sediments on contact with hot lava flowing along the flank of the SEC or, alternatively, to gravitational collapse of a destabilised portion of the eastern flank of the crater. However, several lines of evidence suggest that these models do not adequately explain the paroxysm, which we propose was associated with the explosive emission of magma during the rapid opening of an ESE-WNW-oriented fracture at the eastern base of the SEC. Moreover, geochemical data of the products associated with this episode show that they are the most primitive and gas-rich among those erupted during the entire 2006 period. We suggest that the paroxysm of November 16, 2006, which occurred at base of the SEC, was a magma outburst due to rapid ground fracturing related to a drop in confining pressure upon the underlying dyke consequent to the sliding of the eastern flank of the SEC cone. Specifically, the unloaded shallow portion of the feeding dyke did not restrain the arrival of a new batch of gas-rich magma, which worked its way out by fracturing the base of the niche at its weakest point. This paroxysm appears significant because it reveals the potential development of syn-eruptive dynamics acting directly on the uppermost portion of the plumbing system which is able to generate pyroclastic flows even on basaltic volcanoes such as Mount Etna. [ABSTRACT FROM AUTHOR]

Abstract: The enrichment in potassium shown by the basic lavas erupted at Mount Etna volcano after 1971 (K2O max~2.2wt.%) has been considered by previous researchers to be too high to be related to simple crystal fractionation and instead linked this high K2O content to either crustal assimilation or changes in the magma source. Unfortunately all existing models for the post-1971 K2O enrichment fail to explain the phenomenon satisfactorily leaving the question still open. We present a critical re-examination of published data for major elements (633 whole rock analyses), trace elements (376 whole rock analyses) and isotopic ratios (136 87Sr/86Sr analyses), for historical and pre-historical lavas. Potassium enrichment is not limited to the products of the last 35years. A comparable increase in potassium is noticed in lavas erupted during the pre-historic phase of the recent Mongibello (K2O max~2.5wt.%) and in lavas related to the early phase of the ancient Mongibello (K2O max~3wt.%). Moreover, data from melt inclusions in olivines from the 2001 and 2002 eruptions, reveal that potassium contents remain constant for melts with entrapment pressure between 490 to 100MPa and increase significantly in melts entrapped at pressures below~100MPa. We propose that supercritical fluids coming from deeper magmas and carrying alkali Cl-complexes migrate through basic to intermediate magmas residing in the shallow feeding system. As chlorine exsolves and leaves the system alkalis are released contributing to the observed potassium enrichment of the shallow magma. Fluctuations of the volatiles influx throughout time are likely related to the magma supply rate. Considering that the amount of magma entering a plumbing system is determined by the rate of regional extension, the flux of alkali Cl-complexes entering the melt might be related to an extensional regime acting in the Etnean area. [ABSTRACT FROM AUTHOR]

Large variations of the CO2 flux through the soil were observed between November 2002 and January 2006 at Mt. Etna volcano. In many cases, the CO2 flux was strongly influenced by changes in air temperature and atmospheric pressure. A new filtering method was then developed to remove the atmospheric influences on soil CO2 flux and, at the same time, to highlight the variations strictly related to volcanic activity. Successively, the CO2 corrected data were quantitatively compared with the spectral amplitude of the volcanic tremor by cross correlation function, cross-wavelet spectrum and wavelet coherence. These analyses suggested that the soil CO2 flux variations preceded those of volcanic tremor by about 50 days. Given that volcanic tremor is linked to the shallow (a few kilometer) magma dynamics and soil CO2 flux related to the deeper (~12 km b.s.l.) magma dynamics, the “delayed similarity” between the CO2 flux and the volcanic tremor amplitude was used to assess the average speed in the magma uprising into the crust, as about 170–260 m per day. Finally, the large amount of CO2 released before the onset of the 2004–2005 eruption indicated a deep ingression of new magma, which might have triggered such an eruption. [ABSTRACT FROM AUTHOR]

Abstract: Vesicle populations in volcanic pumice provide a partial record of shallow magma ascent and degassing. Here we compare pumice textures from the well-characterized 79AD Vesuvius eruption to those generated during isothermal decompression experiments. Three series of experiments were conducted using starting material from the first two phases of the eruption (eruptive units EU1 and EU2). Samples were decompressed from 100 or 150MPa to final pressures of 10–25MPa using conditions appropriate for simulating eruption conditions (T =850°C, dP/dT =0.25MPa/s). The experiments differed not only in starting material but also in temperature at which samples were annealed prior to decompression, which determined the initial number of crystals present in the melt. Results show that experiments approach the vesicle number densities and sizes of pumice samples, but show narrower size distributions. The wider size range of pumice samples suggests continuous, rather than instantaneous nucleation, which may reflect non-linear rates of decompression. All experiments exhibited equilibrium degassing, a process that was probably aided by heterogeneous bubble nucleation on oxide microlites. We conclude that delayed bubble nucleation cannot explain the explosivity of the Vesuvius eruption, which instead appears to require high rates of magma decompression. [Copyright &y& Elsevier]

Abstract: We studied the stress effects of the topography load on dike propagation by considering the results from analogue experiments; in addition, we refined the results by applying numerical simulations using the finite element method (FEM) in order to also consider the medium rheology and real topography. We investigated the dike deflection observed during the final dike emplacement accompanying Etna''s 2001 eruption. We cross-related the information on the position of the dike from ground deformation modelling with the numerical simulation results with the aim of estimating the final excess pressure of the dike when it started to deflect, which proved to be about 4–8MPa. Assuming that the pressure decreases linearly with the volume of magma moving from the chamber into the dike, we estimated 7–15MPa as the initial overpressure accumulated at the intermediate magma chamber before its breakout. Although the previous modelling overestimated the stress, the approach presented here leads to infer a compatible stress with the strength of the rocks. [Copyright &y& Elsevier]

Magmatic processes triggering eruptions at Campi Flegrei caldera (southern Italy) and their relationships with the widespread emissions of fluids and caldera unrest episodes, are poorly constrained. The 4.1kaB.P. Agnano–Monte Spina eruption, the reference event for a future large-size explosive eruption at Campi Flegrei, was investigated to shed light, through melt inclusion and isotope analyses, on the geochemical processes operating in the plumbing system. Chemical and isotopic data on whole rocks and glasses suggest that at least two magma batches mixed during the course of the eruption. Melt inclusion data highlight the pre-eruption storage conditions of two magmatic end-members. One end-member is like the less differentiated (shoshonitic) Campi Flegrei erupted magma, while the other could be a residual of the Neapolitan Yellow Tuff magma. Mixing between these two components was driven by a large gas phase which sustained the ascent of magmas of deep provenance. The H2O and CO2 contents in pyroxene-hosted melt inclusions yield entrapment pressures between 107 and 211MPa, corresponding to depths between 4 and 8km. The degassing trends reveal two extreme patterns. One pattern, already documented in the literature, is the volatile signature of poorly differentiated magmas ascending from more than 8km depth, while the other is related to a gas-dominated magma, flushed by a CO2-rich gas phase partly released from the deep reservoir. This study provides a conceptual frame for unrest phases at Campi Flegrei, such as the 1982–84 event. Uplift phases can be related to closed-system ascent of magmas and fluids from more than 8km depth, and their emplacement at shallow levels. This leads the shallow system to store, and then progressively release, the accumulated gas. In this view, both unrest episodes and eruptions could be strongly influenced by both the achievement of a critical upper limit of gas storage in the shallow magmatic reservoir and the stress and fracturing state of the roof rocks. The present results help to constrain the pre-eruptive conditions expected at Campi Flegrei caldera in case of a future large-size eruptive event. [Copyright &y& Elsevier]

Abstract: The Secche di Lazzaro (SDL) phreatomagmatic activity, with the associated Neostromboli sector collapse, represents the most powerful activity of the last 6ky at Stromboli. As revealed by its present-day activity, Stromboli is one of the most eruptive volcanoes in Italy, and flank instability, along its NW flank, is a common process. Volcano instability is often dramatised by explosive eruptions, thus it is of crucial importance to understand the linking between volcano collapse and the plumbing system itself. The possible role of pre-eruptive magmatic processes as triggers of explosive eruptions can be mainly preserved by minerals and revealed by petrochemical studies. We studied the juvenile components (scoria and pumice) of the pyroclastic deposits from the SDL phreatomagmatic activity with the aim to understand the eruption–collapse link. The SDL pyroclastic sequence has been investigated in three different outcrops: at Secche di Lazzaro (SDL-SW sequence), at Vallone del Monaco (SDL-S) and along the old path from Stromboli village to the active craters (SDL-N). Juvenile components are KS-shoshonites similar to the most evolved lavas erupted at the end of the Neostromboli potassic period. Our study indicates that the SDL system is strongly heterogeneous and made up by at least two different sequences (SDL-N and SDL-SW/SDL-S) with different textural characteristics of the deposits and composition of the juvenile components. Mineral chemistry data show a variable presence of recycled crystals (antecrysts), possibly deriving from the previous Neostromboli activity (up to 13ky ago). Whole rocks are characterised by small but significant differences between the SDL-N and the southern samples, pointing out the presence of compositionally different potassic magmas and the crystallization and recycling of slightly different mineral assemblages. A clear isotope heterogeneity has been also found and explained by the presence of 10% minimum of less radiogenic antecrysts, whereas crustal contamination would have only affected the higher Sr-radiogenic residual melt. These data suggest that the SDL phreatomagmatic eruptions were fed by compositionally distinct potassic magmas, which rested and evolved in two shallow magma conduits when the magma-supply ceased in the waning phase of the Neostromboli activity. Our results also rule out the occurrence of new arrivals of refreshing magmas in the SDL feeding system, as well as other internal magma-related causes, as triggers for the SDL explosive eruptions. Accordingly, external collapse-related causes seem effectively more suitable for triggering the SDL phreatomagmatic eruptions by decompression of the magmatic systems. We also suggest the SDL-N and SDL-SW/SDL-S sequences are generated by two respective explosive events, separated in time and/or space. They can be respectively related to multiple failures of Sciara del Fuoco which successively depressurised the SDL-N and the SDL-SW/SDL-S magma conduits. [Copyright &y& Elsevier]