Search

This study focus on the Mt Etna December 2018 eruption with the aim of investigating the geochemical characteristics of the feeding magma. New data on major and trace element geochemistry of olivine-hosted melt inclusions (MI) in volcanic products are presented together with the noble gas geochemistry of fluid inclusions (FI) in olivines. The noble gas geochemistry of fluid inclusions (FIs) in olivines was also investigated. The major element composition of MIs is variable from tephrite/trachybasalt to phonotephrite/basaltic trachyandesite, with SiO2 = 45.51-52.72 wt%, MgO = 4.01-6.02 wt%, and CaO/Al2O3 = 0.34-0.72. Trace element patterns of MIs present a typical enrichment in LILE and LREE, depletion in HFSE, and relatively fractionated REE patterns: (La/Lu) N= 18.8-41.08, with Eu/Eu* = (0.5-1.8). Positive anomalies in Sr (Sr/Sr* = 0.8-2.3) and Ba can be ascribed to the assimilation of plagioclase-rich cumulates in the magmatic reservoir. The variable Ba/La (9.8-15.8), K/Nb (260-1037), Ce/Nb (1.9-3.4), Rb/La (0.4-1.6), and Ba/Nb (10.8-25.8) ratios reveal mixing between two types of end-member magmas comparable to those emitted from 1) the 2001 Upper Vents and 2002-03 Northern Fissures (Type-1) and 2) the 2001 Lower Vents and 2002-03 Southern Fissures (Type-2), respectively. Type-2 represents a magma that was under the influence of a crustal component, whereas Type-1 is compatible with a HIMU-MORB-type heterogeneous mantle source. It appears that the 2018 MIs have captured the two different types of magmas, and the lack of homogenization may imply a very fast ascent (a few months). Compatible with the contemporary presence of primordial HIMU-MORB and crust-contaminated end-members are the data on noble gases from FI that highlighted an ³He/[sup 4]He value of 6.5-6.6Ra. The hypothesis of two different types of magmas, identified by the trace element geochemistry in MIs, is, thus, reinforced by helium isotopic data on FI of the 2018 eruption together with data from other Etnean eruptions and allows the inference of a bicomponent magma mixing. [ABSTRACT FROM AUTHOR]

The South-East Crater (SEC) at Mt. Etna started a period of lava fountaining in December 2020, producing over 60 paroxysms until February 2022. The activity had an intense sequence from February 16 to April 1, 2021, totaling 17 paroxysmal events separated by repose times varying from 1 to 7 days. The eruptive sequence was extensively monitored, providing a unique opportunity to relate the chemistry and texture of the erupted products to eruption dynamics. We investigate the temporal evolution of the magmatic system through this eruptive sequence by quantifying variations in the composition and texture of clinopyroxene. Clinopyroxene major element transects across crystals from five representative lava fountains allow us to determine the relative proportions of deep versus shallow-stored magmas that fed these events. We use hierarchical clustering (HC), an unsupervised machine learning technique, to objectively identify clinopyroxene compositional clusters and their variations during this intense eruptive phase. Our results show that variations of monitoring parameters and eruption intensity are expressed in the mineral record both as changes in cluster proportions and the chemical complexity of single crystals. We also apply random forest thermobarometry to relate each cluster to P-T conditions of formation. We suggest that the February–April 2021 eruptive sequence was sustained by the injection of a hotter and deeper magma into a storage area at 1–3 kbar, where it mixed with a slightly more evolved magma. The February 28 episode emitted the most mafic magma, in association with the highest mean lava fountain height and highest time–averaged discharge rate, which make it the peak of the analyzed eruptive interval. Our results show that after this episode, the deep magma supply decreased and the erupted magma become gradually more chemically evolved, with a lower time–average discharge rate and fountain height. We propose this approach as a means to rapidly, objectively, and effectively link petrological and geophysical/geochemical monitoring during ongoing eruptions. We anticipate that the systematic application of this approach will serve to shed light on the magmatic processes controlling the evolution of ongoing eruptions. [ABSTRACT FROM AUTHOR]

Mt Etna has made headlines over the last weeks and months with spectacular eruptions, some of them highly explosive. This type of paroxysmal eruptive behaviour is characteristic of Etna's activity over the past few decades and so it is no surprise that Etna is among the most active volcanoes worldwide. Etna is well‐known for its extraordinary geology and due to its repeated eruptive activity it provides a continuous supply of new scientific opportunities to understand the inner workings of large basaltic volcanic systems. In addition to its scientific value, Etna is also a world famous tourist attraction and has been listed as a UNESCO World Heritage site in 2013 for its geological and cultural value and not least for its fine agricultural products. Etna's status as an iconic volcano is not a recent phenomenon; in fact, Etna has been a literary fixture for at least 3000 years, giving rise to many ancient myths and legends that mark it as a special place, deserving of human respect. From the ancient eruptions to the latest events in February–April 2021, people try to explain and understand the processes that occur within and beneath the volcano. In this article, we briefly summarize the recent eruptive activity of Etna as well as the ancient myths and legends that surround this volcano, from the underground forge of Hephaestus to the adventures of Odysseus, all the way to the benefits and dangers the volcano provides to those living on its flanks today. [ABSTRACT FROM AUTHOR]

A lengthy period of eruptive activity from the summit craters of Mt. Etna started in January 2011. It culminated in early December 2015 with a spectacular sequence of intense eruptive events involving all four summit craters (Voragine, Bocca Nuova, New Southeast Crater, and Northeast Crater). The activity consisted of high eruption columns, Strombolian explosions, lava flows and widespread ash falls that repeatedly interfered with air traffic. The most powerful episode occurred on 3 December 2015 from the Voragine. After three further potent episodes from the Voragine, activity shifted to the New Southeast Crater on 6 December 2015, where Strombolian activity and lava flow emission lasted for two days and were fed by the most primitive magma of the study period. Activity once more shifted to the Northeast Crater, where ash emission and weak Strombolian activity took place for several days. Sporadic ash emissions from all craters continued until 18 December, when all activity ceased. Although resembling the summit eruptions of 1998–1999, which also involved all four summit craters, this multifaceted eruptive sequence occurred in an exceptionally short time window of less than three days, unprecedented in the recent activity of Mt. Etna. It also produced important morphostructural changes of the summit area with the coalescence of Voragine and Bocca Nuova in a single large crater, the “Central Crater”, reproducing the morphological setting of the summit cone before the formation of Bocca Nuova in 1968. The December 2015 volcanic crisis was followed closely by the staff of the Etna Observatory to monitor the on-going activity and forecast its evolution, in accordance with protocols agreed with the Italian Civil Protection Department. [ABSTRACT FROM AUTHOR]

Primitive basaltic magmas are crucial in the study of the geochemical heterogeneity documented in Etna magmas and their inferred mantle sources. We undertook a systematic sampling of the less evolved basalts (Mg# > 50) erupted over the last 15 ka, a time period which corresponds to the activity of the youngest volcanic edifice of Mt. Etna complex, i.e. Mongibello volcano. We focused on lava flows and pyroclastites emplaced during ‘ deep-dyke fed ’ (DDF) eruptions which were driven by the rapid ascent of deeply-rooted magma intrusions that bypassed the shallow plumbing system of the volcano. All the samples were analyzed by the same laboratory to avoid analytical bias, to build a comprehensive dataset on their major and trace element compositions and to propose a coherent framework for interpreting the geochemical fingerprints of present-day Etna basalts. Trace element modeling, together with literature data for Sr isotopes, gave insight into long-term magmatic processes related to different melting degrees of the heterogeneous mantle beneath Mt Etna. DDF magma batches provide good snapshots of their mantle source heterogeneities that point to the variable involvement of clinopyroxenitic lithology, Rb– 87 Sr–Cl-rich fluid component(s) possibly controlled by their source mineralogy, and slab-derived fluids selectively enriched in alkalis (Rb, K). The ongoing alkali (Rb, K) enrichment of the present-day magmas, well manifest since the 1970s, is decoupled from that of Sr and Cl. We propose that this process is linked to mantle source composition and is concomitant with changes in both volcanological and seismotectonic patterns of the volcano. There is no time evolution of DDF magma chemistry. [ABSTRACT FROM AUTHOR]

Abstract: Mt. Etna is an active basaltic volcano where both flank and summit eruptions take place. In recent decades, the South-East summit crater (SEC) has in particular been characterized by ‘episodic’ eruptions, consisting of recurrent lava fountains associated with lava flow emissions and lasting from a few weeks to months. Recent volcanic activity shows that, if there is a transition from an episodic summit eruption to a flank eruption, then this usually takes place while the last paroxysm of the episodic eruption is still underway. By contrast, the 2007–08 episodic eruption at SEC was followed by the 2008–09 flank activity which started three days after the conclusion of the last paroxysm, coinciding with the strong earthquake (M=7.9) in Sichuan (China), whose perturbations were recorded by the monitoring network of Mt. Etna. We therefore investigated the transition from a summit episodic eruption at SEC to flank activity utilizing a petrologic study of the products erupted from 2007 to 2009, integrated with literature data. The compositional variability of the products may largely be explained by a mixing between an evolved magma stored in the SEC reservoir and a more primitive magma which intrudes it. In the studied period, the most significant episodes of magma recharge occurred before the onset of the 2007–08 episodic eruption and during the 2008–09 flank activity, more precisely before June 2008. According to previous studies, the seven paroxysms of the 2007–08 episodic eruption at SEC have been interpreted as resulting from the disruption of a foam layer at the top of the SEC reservoir which was rebuilt before each subsequent episode. The transition from the 2007–08 episodic eruption at SEC to the 2008–09 flank activity was essentially triggered by the Sichuan earthquake which caused a variation of dynamic stress. It caused the volatile exolution, the pressurization of SEC stored magma, and the consequent fracturing of the surrounding rocks where magma intruded to then be erupted during the 2008–09 flank activity. [Copyright &y& Elsevier]

Various xenoliths have been found in lavas of the 1763 ('La Montagnola'), 2001, and 2002-03 eruptions at Mt. Etna whose petrographic evidence and mineral chemistry exclude a mantle origin and clearly point to a cognate nature. Consequently, cognate xenoliths might represent a proxy to infer the nature of the high-velocity body (HVB) imaged beneath the volcano by seismic tomography. Petrography allows us to group the cognate xenoliths as follows: i) gabbros with amphibole and amphibole-bearing mela-gabbros, ii) olivine-bearing leuco-gabbros, iii) leuco-gabbros with amphibole, and iv) Plg-rich leuco gabbros. Geobarometry estimates the crystallization pressure of the cognate xenoliths between 1.9 and 4.1 kbar. The bulk density of the cognate xenoliths varies from 2.6 to 3.0 g/cm. P wave velocities (V), calculated in relation to xenolith density, range from 4.9 to 6.1 km/s. The integration of mineralogical, compositional, geobarometric data, and density-dependent V with recent literature data on 3D V seismic tomography enabled us to formulate the first hypothesis about the nature of the HVB which, in the depth range of 3-13 km b.s.l., is likely made of intrusive gabbroic rocks. These are believed to have formed at the 'solidification front', a marginal zone that encompasses a deep region (>5 km b.s.l.) of Mt. Etna's plumbing system, within which magma crystallization takes place. The intrusive rocks were afterwards fragmented and transported as cognate xenoliths by the volatile-rich and fast-ascending magmas of the 1763 'La Montagnola', 2001 and 2002-03 eruptions. [ABSTRACT FROM AUTHOR]

We present the application of a classification method based on Kohonen maps and fuzzy clustering to geochemical analyses of volcanic products erupted on Mt. Etna from 1995 to 2005. Based on 13 major and trace elements, the classification allows a new way to visualize distinct compositional features of magma both considering long period as well as single eruptive events, such as in 2001 and 2002-03 flank eruptions. Products of the various vents do not necessarily form homogeneous groups, but show clear trends of chemical evolution with time. Using a convenient color code, the graphical visualization of the results in just a single picture allows the rapid identification of the compositional features of each sample and their comparison with all the products analyzed in the 10-year-long time span. This single picture accounts for the mutual interactions of the 13 components avoiding shortcomings of classical low-dimensional plots where components relevant for the discrimination have to be found in a priori study of many diagrams. On the basis of the synoptic information provided by pattern classification, we identify links between the products of different eruptive vents which deliver a reliable picture of a multifaceted plumbing system, in agreement with geochemical and geophysical evidence reported in literature. The analysis of the 13-dimensional data set using the Kohonen maps and fuzzy clustering simultaneously turned out to be straightforward and easy. Accordingly, the results of this application will be useful also as a contextual data set for new data in future ongoing eruptive episodes. [ABSTRACT FROM AUTHOR]

Abstract: Mt. Etna volcano is located in a complex tectonic setting, with large sectors of its eastern flank sliding seaward at different rates. According to recent petrologic studies, the Etna''s plumbing system has a multifaceted geometry, variable in space and time and consisting of storage zones at different depths, where magma ascending to the surface undergoes various processes, mainly fractional crystallization and mixing. In this framework we investigated a possible cause–effect relationship between the flank displacement and pre-eruptive magmatic processes in the shallow plumbing system (<5km b.s.l.) during the decade 1995–2005. In particular, we analyzed petrography, mineral chemistry, geochemistry, Sr and Nd isotopes of the products emitted from 1995 to 2001 by the four summit craters of Etna (South-East, North-East, Bocca Nuova and Voragine). Results integrated with petrologic data already available in literature for the investigated decade, allowed us to better constrain the temporal evolution of the magmatic processes occurring in the Etna''s shallow plumbing system (mainly mixing between compositionally and isotopically distinct magmas and fractional crystallization), and to make inferences on its geometry. Furthermore, a comparison between petrologic data and deformative patterns evidences that, from 1995 to July 2001, the aforementioned pre-eruptive magmatic processes did not significantly influence the volcano eastern flank dislocation, which stayed slow and fairly regular. By contrast, the onset of the 2001 flank eruption leads to an acceleration of the movement as a consequence of the ascent, of a primitive, volatile-rich, sub-aphyric basaltic magma from a deeper (about 10km b.s.l.) reservoir, during the 2001 and 2002–03 activity. At least for the decade 1995–2005, pre-eruptive magmatic processes in the shallow portion (<5km b.s.l.) of Etna''s plumbing system, did not directly affect the movement of the volcano''s eastern flank. Conversely, a magma intrusion which forcefully opens a new path from a deeper zone (about 10km b.s.l.) of the plumbing system, causes a dramatic increase of deformative pattern, which strongly accelerates the slide of the eastern flank, as occurred during both 2001 and 2002–03 eruptions. [Copyright &y& Elsevier]

Mt. Etna, in Sicily (Italy) is well known for frequent effusive and explosive eruptions from both its summit and flanks. South-East Crater (SE Crater), one of the four summit craters, has been the most active in the last 20 years and often produces episodic lava fountains over periods lasting from a few weeks to months. The most striking of such eruptive phases was in 2000. Sixty four lava fountains, separated by quiescent intervals and sometimes associated with lava overflows, occurred that year between January and June, a time period during which we consider the volcano to have been in episodic eruption. This paper presents mainly results of petrochemical investigations carried out on both tephra and lavas collected during a number of the lava fountain episodes in 2000. The new data have been integrated with volcanological and seismic information in order to correlate the features of the eruptive activity with magma-gas dynamics in the plumbing system of SE Crater. The main findings allow us to characterise the 2000 episodic eruption in the framework of the recent SE Crater activity. In particular, we infer that the onset of the 2000 eruption was triggered by the ascent of new, more primitive and volatile-rich magma that progressively intruded into the SE Crater reservoir, where it mixed with the resident, more evolved magma. Furthermore, we argue that the 2000 SE Crater lava fountains largely resulted from the instability of a foam layer accumulated at the top of the underlying reservoir and rebuilt prior to each episode, in agreement with the collapsing foam model for lava fountains. [ABSTRACT FROM AUTHOR]

Strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions. However, the transition between these two eruptive styles and their source mechanisms are still debated. We use textural and compositional studies to characterize pyroclastic material from both the Strombolian and Hawaiian-style fire fountain phases of the January-June 2000 Etna activity. We find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes. Overall, magma that forms Strombolian scoria is far more crystallized, less vesicular, and more evolved, indicating strong volatile depletion and longer residence time before being erupted. Fire fountain scoria indicates a fast-rising magma with evidence of moderate syneruptive volatile ex-solution. The new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains, and to frame the transition from Strombolian explosions to fire fountain activity into a model that may apply to future eruptions at Mount Etna as well as other active basaltic volcanoes. [ABSTRACT FROM AUTHOR]

Lava tubes are often coated with spectacular lava stalactites that are thought to form by a process of lava remelting. Here, we present results from lava stalactites collected inside a master lava tube that fed the 1792-1793 Etna flank eruption, which show features rather different from their Hawaiian or Icelandic counterparts. We analyzed three types of stalactites recognized at Mt. Etna on the basis of their morphology, and compared their features with those of the lava flow hosting the tube. Three-dimensional morphologic analyses by SEM, petrographic observations, and mineral and glass composition measured by SEM-EDS, allowed us to infer processes and Conditions of stalactite formation. Our results indicate that in all the analyzed stalactites, the nature, abundance and composition of phenocrysts is similar to that of the host lava flow. This finding suggests a common mechanical origin for different types of stalactites, caused by drainage of the tube and dripping of fluid lava from the roof. However, the composition of interstitial glass is significantly different from that of the glassy groundmass measured in historical volcanic rocks of Mt. Etna and suggests that, once stalactites solidified, they were affected by a process of partial melting. Partial melting involved between 12 and 25% of the bulk rock, causing the wide compositional variation and enrichment in K2O measured in our samples. [ABSTRACT FROM AUTHOR]

Buoyancy controls the ability of magma to rise, its ascent rate and the style of the eruptions. Geophysical, geological and petrological data have been integrated to evaluate the buoyancy of magmas at Mt Etna. The density difference between host rocks and magmas is mainly related to the amount of H2O dissolved in the magma and to the bubble-liquid separation processes. In the depth interval 22–2 km b.s.l. highly hydrated (H2O ∼ 3%) basaltic magmas or mixtures of bubbles + liquid have positive buoyancy and rise rapidly. Conversely, bubble-depleted liquids, with an intermediate H2O content (∼ 1.5%), having neutral buoyancy, will spread out and form magmatic reservoirs at different depths until cooling/crystallization further modify composition and density. These different processes account for the magma compositions, location of magmatic reservoirs as determined by geophysical methods, and the complex eruptive cycles (slow effusions, fire fountains and Plinian eruptions) that have been observed in the history of the volcano. Terra Nova, 00, 1–7, 2004 [ABSTRACT FROM AUTHOR]

Globular and microglobular peperites, with mingled sediment in millimetric to decimetric domains, are described from inside pillow lavas at Acicastello Castle Rock, Mt. Etna, Sicily for the first time. The peperites now comprise basalt and minor remnants of fine-grained detrital material, with smectite and zeolite crystallised during late hydrothermal activity. We propose that peperites formed when the magma, ascending towards the surface, intruded and intermixed with the unconsolidated wet Pleistocene bluish marly clays of the substrate. Subsequently they were transported by the uprising magma from the source region towards the surface, where they are preserved in pillow lavas. [Copyright &y& Elsevier]

The tectonic escarpments locally known as ‘Timpe’ cut a large sector of the eastern flank of Etna, and allow an ancient volcanic succession dating back to 225 ka to be exposed. Geological and volcanological investigations carried out on this succession have allowed us to recognize relevant angular unconformities and volcanic features which are the remnants of eruptive fissures, as well as important changes in the nature, composition and magmatic affinity of the exposed volcanics. In particular, the recognition in the lower part of the succession of important and unequivocal evidence of ancient eruptive fissures led us to propose a local origin for these volcanics and to revise previous interpretations which attributed their westward-dipping to the progressive tectonic tilting of strata. These elements led us to reinterpret the main features of the volcanic activity occurring since 250 ka BP and their relationship with tectonic structures active in the eastern flank of Etna. We propose a complex paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna, in which the Timpe fault system played the role of the crustal structure that allowed the rise and eruption of magmas in the above considered time span. [Copyright &y& Elsevier]

Volcanic hazards associated with lava flows advancing on snow cover are often underrated, although sudden explosions related to different processes of lava-snow/ice contact can occur rapidly and are only preceded by small, easily underrated precursors. On 16 March 2017, during a mildly effusive and explosive eruption at Mount Etna, Italy, a slowly advancing lava lobe interacted with the snow cover to produce a sudden, brief sequence of explosions. White vapor, brown ash, and coarse material were suddenly ejected, and the products struck a group of people, injuring some of them. The proximal deposit formed a continuous mantle of ash, lapilli, and decimeter-sized bombs, while the ballistic material travelled up to 200 m from the lava edge. The deposit was estimated to have a mass of 7.1 ± 0.8 x 104 kg, which corresponds to a volume of 32.0 ± 3.6 m³ of lava being removed by the explosion. Data related to the texture and morphology of the ejected clasts were used to constrain a model of lava-snow interaction. The results suggest that the mechanism causing the explosions was the progressive build-up of pressure due to vapor accumulation under the lava flow, while no evidence was found for the occurrence of fuel-coolant interaction processes. Although these low-intensity explosions are not particularly frequent, the data set collected provides, for the first time, quantitative information about the processes involved and the associated hazard and suggests that mitigation measures should be established to prevent potentially dramatic accidents at worldwide volcanoes frequented by tourists and with fairly easy access, such as Etna. [ABSTRACT FROM AUTHOR]

Ashes emitted during volcanic explosive activity present peculiar surface chemical and mineralogical features related in literature to the interaction in the plume of solid particles with gases and aerosols. The compositional differences of magmas and gases, the magnitude, intensity and duration of the emission and the physical condition during the eruption, strongly influence the results of the modification processes. Here we report the characterization of the products emitted during the 2013 paroxysmal activity of Mt. Etna. The surface features of the ash particles were investigated through X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM) allowing the analysis at nanometer scale. TEM images showed on the surface the presence of composite structures formed by Ca, Mg and Na sulphates and halides and of droplets and crystals of chlorides; nanometric magnesioferrite and metallic iron dendrites are observable directly below the surface. From the chemical point of view, the most external layer of the volcanic glassy particles (<5 nm), analysed by XPS, presents depletion in Si, Mg, Ca, Na and K and strong enrichment in volatile elements especially F and S, with respect to the inner zone, which represents the unaltered counterpart. Below this external layer, a transition glassy shell (thick 50–100 nm) is characterized by Fe, Mg and Ca enrichments with respect to the inner zone. We propose that the ash particle surface composition is the result of a sequence of events which start at shallow depth, above the exsolution surface, where gas bubbles nucleate and the interfaces between bubbles and melt represent proto-surfaces of future ash particles. Enrichment of Ca, Mg and Fe and halides may be due to the early partition of F and Cl in the gas phase and their interaction with the melt layer located close to the bubbles. Furthermore the formation of volatile SiF 4 and KF explain the observed depletion of Si and K. The F enrichment in the external ∼50 nm thick layer of the glassy particles suggests the resorption of this element during the rise from depth less than 400 m below the summit vent. During the eruption, the gas/ash interaction persists inside the plume where further changes on the particle surface occurs. Gaseous S, Cl and F react causing the formation of solid Ca, Mg, Na and K compounds, while SiF 4 was released as volatile phase and HF was physisorbed. Finally, in the low temperature plume zone, halides previously formed continuously react with gases producing sulfates. [ABSTRACT FROM AUTHOR]

Between January 2011 and April 2012, the Southeast Crater (SEC) on Mount Etna was the site of 25 episodes of lava fountaining, which led to the construction of a new pyroclastic cone on the eastern flank of the SEC. During these episodes lava overflows reached 4.3km in length with an area of 3.19km2 and a volume of 28×106 m3. The new cone, informally called New Southeast Crater (NSEC), grew over a pre-existing subsidence depression (pit crater), which had been formed in 2007–2009. The evolution of the NSEC cone was documented from its start by repeated GPS surveys carried out both from a distance and on the cone itself, and by the acquisition of comparison photographs. These surveys reveal that after the cessation of the lava fountains in April 2012, the highest point of the NSEC stood 190m above the pre-cone surface, while the cone volume was about 19×106 m3, representing 38% of the total (bulk) volume of the volcanic products including pyroclastic fallout erupted in 2011–2012, which is 50×106 m3 (about 33×106 m3 dense-rock equivalent). Growth of the new cone took place exclusively during the paroxysmal phases of the lava fountaining episodes, which were nearly always rather brief (on the average 2h). Overall, the paroxysmal phases of all 25 episodes represent 51h of lava fountaining activity — the time needed to build the cone. This is the fastest documented growth of a newborn volcanic cone both in terms of volume and height. Mean effusion rates during the lava fountaining episodes on 20 August 2011 (E11), as well as 12 and 24 April 2012 (E24 and E25) exceeded 500m3/s (with maximum rates of 980m3/s during E11) and thus they are among the highest effusion rates ever recorded at Etna. The composition of the erupted products varies in time, reflecting different rates of magma supply into the shallow feeding system, but without notable effects on the eruptive phenomenology. This implies that the dynamics leading to the episodic lava fountaining was largely, though not entirely, controlled by the repeated formation and collapse of a foam layer in the uppermost portion of the magmatic reservoir of the NSEC. [ABSTRACT FROM AUTHOR]

Abstract: The major elements, trace elements and Sr and Nd isotopes of selected Etnean primitive rocks (<15kyBP) were studied in order to characterize their mantle source. The noble-gas geochemistry of fluid inclusions in minerals from the same lavas was also investigated. The major element compositions of whole rocks and minerals showed that these products are among the most primitive at Mt. Etna, comprising 6.3–17.5wt.% MgO. The variable LREE (Light Rare Earth Elements) enrichment relative to MORB (Mid-Ocean Ridge Basalt) (Lan/Ybn =11–26), together with the patterns of certain trace-element ratios (i.e., Ce/Yb versus Zr/Nb and Th/Y versus La/Yb), can be attributed to varying degrees of melting of a common mantle source. Numerical simulations performed with the MELTS program allowed the melting percentages associated with each product to be estimated. This led us to recalculate the hypothetical parental trace-element content of the Etnean mantle source, which was common to all of the investigated rocks. The characteristics of the Sr, Nd and He isotopes confirmed the primitive nature of the rocks, with the most-depleted and primitive lava being that of Mt. Spagnolo (SPA; 143Nd/144Nd=0.512908 87Sr/86Sr=0.703317–0.703325 and 3He/4He=7.6 Ra), and highlighted the similarity of the mantle sources feeding the volcanic activity of Mt. Etna and the Hyblean Plateau (a region to the south of Mt. Etna and characterized by older magmatism than Mt. Etna). The coupling of noble gases and trace elements suggests an origin for the investigated Etnean lavas from melting of a Hyblean-like mantle, consisting of a two-component source where a peridotitic matrix is veined by 10% pyroxenite. A variable degree of mantle contamination by crustal-like fluids, probably related to subduction, is proposed to explain the higher Sr-isotope and lower Nd-isotope values in some rocks (143Nd/144Nd up to 0.512865 and 87Sr/86Sr up to 0.703707). This process probably occurred in the source prior to magma generation, refertilizing some portions of the mantle. Accordingly, the estimated degree of melting responsible for each magma appears to be related to its 87Sr/86Sr enrichment. In contrast, the decoupling between 3He/4He and 87Sr/86Sr ratios requires the occurrence in the crustal reservoirs of further processes capable of shifting the He isotope ratio towards slightly more radiogenic values, such as magma aging or a contribution of shallow fluid. Therefore, different residence times in the Etnean reservoir and/or various rates of magma ascent could be key parameters for preserving the original He isotope marker of the Etnean mantle source. [Copyright &y& Elsevier]

Abstract: We present the first chlorine isotope compositional data for gases and lavas from Mount Etna (Italy), and to our knowledge, of active Mediterranean volcanism. We investigated lavas erupted and gases discharged during 2008–2011 from a high-temperature fumarole (HT; >300°C) and plume gases from both North East and Central Craters. Most of the samples vary in a narrow range of chlorine isotope composition (δ37Cl values≈0±0.7‰) with gases partially overlapping with rocks. Only HT gases sampled in 2009 have been clearly affected by secondary processes (δ37Cl values>15.9‰), resulting in partial removal of chlorine and isotopic fractionation producing a 37Cl enrichment in the residual gaseous HCl. These secondary processes also affect, although to a lesser extent, plume gases from North East Crater (NEC). Although post-magmatic processes are able to modify the chlorine isotope composition, δ37Cl values are not affected by magma degassing for residual fractions ≥0.3 in the melt, or any effect is within our data variability. Finally, δ37Cl values and Cl/K ratios of magmatic chlorine constrain the Etnean source to be compatible with depleted mantle (DMM) contaminated by altered oceanic crust (AOC), in agreement with indications from more common isotopic tracers of mantle processes. [Copyright &y& Elsevier]

At active volcanoes, distinct eruptions are preceded by complex and different precursory patterns; in addition, there are precursory signals that do not necessarily lead to an eruption. The main purpose of this paper is to present an unprecedented application of the recently developed code named BET_EF (Bayesian Event Tree_Eruption Forecasting) to the quantitative estimate of the eruptive hazard at Mt. Etna volcano. We tested the model for the case history of the July-August 2001 flank eruption. Anomalies in geophysical, geochemical and volcanological monitoring parameters were observed more than a month in advance of the effective onset of the eruption. As a consequence, eruption probabilities larger than 90% were estimated. An important feature of the application of BET_EF to Mt. Etna was the probabilistic estimate of opening vent locations. The methodology allowed a clear identification of assumptions and the monitoring of parameter thresholds and provided rational means for their revision if new data or information are incoming. [ABSTRACT FROM AUTHOR]