Geochemical Patterns Classification of recent Mt. Etna volcanic products based on a synopsis of Kohonen Maps and Fuzzy Clustering

During the last two decades Mt. Etna experienced many summit and flank eruptions with different styles of activity, ranging from quiet lava effusion to explosive activity consisting of Strombolian explosions and/or spectacular fire fountains. This complex picture entails the presence of a complex plumbing system where magma dynamics strongly controls both the eruptive style and magma differentiation. All these eruptive events have furnished volcanic products on which systematic petrographic and geochemical analyses have been carried out since the mid 1990s. In particular, the content of major and trace elements of lavas is a key-point to characterize the composition of a magma emitted during an eruption. Petrologic investigations are traditionally based on the interpretation of compositional patterns described by selected oxides and/or elements in binary and ternary petrologic systems. This kind of analysis provides useful information about the magmatic processes occurring in the plumbing system. In this presentation we investigate whether the quality of petrologic investigations is improved by the application of more sophisticated analytical techniques based on the use of a relatively large number of parameters. To this purpose, we selected 13 components, i.e., SiO2, K2O, CaO/Al2O3, Mg#, Th, La, Nb, Nd, Sr, Tb, Cr, Ni and Rb/Nb. This choice brings along the problem of designing a suitable statistics and a convenient visualization of the results. As a way out, we propose advanced concepts of multivariate classification based on a synopsis of Kohonen Maps and Fuzzy Clustering, and apply them to the study of volcanics erupted from Mt. Etna between 1995 and 2005. Lavas erupted during the fire fountains (in 2000) and during the flank eruptions (2001, 2002-03) represent the most primitive products erupted from Mt. Etna in the investigated period. The literature data suggest that during the 2001 and 2002-03 eruptions two magmas with different geochemical characteristics were contemporaneously erupted. One magma type ascended from a deep portion of the plumbing system (> 5 km), and was emitted from the so called “Lower” (2001) and “Southern” vents (2002-03). Another one rose from a shallower reservoir (<5 km) and was erupted from the so called “Upper” (in 2001) and “Northern” vents (in 2002-03). In our analysis the “Lower” and “Southern” vent lavas are assigned to the same cluster ID and are grouped together also in the Kohonen Map. On the other hand, “Upper” vent lavas and “Northern “ vent lavas are clearly distinguished from each other as well as from the afore mentioned products. Volcanics emitted by the South-East crater during the fire fountains in 2000 belong to the same fuzzy cluster as the “Lower” and “Southern” vent lavas, however, a neat distinction with respect to 2001 and 2002-03 lavas becomes evident in the Kohonen Map. Besides this we observe differences in the seismic signal characteristics between the fire fountain events and flank eruptions, supporting the hypothesis that various eruptive sources were active on Mt Etna in 2000, 2001 and 2002-03. The relation of the products to eruptive sources is less clear in the time span between 1995 and 1999, when essentially only the summit craters were active

The December 2018 eruption at Etna volcano: a geochemical study on melt and fluid inclusions

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/4He 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

Monitoring the December 2015 summit eruptions of Mt. Etna (Italy): Implications on eruptive dynamics

A lengthy period of eruptive activity fromthe summit craters ofMt. 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,NewSoutheast Crater, and Northeast Crater). The activity consisted of high eruption columns, Strombolian explosions, lava flows andwidespread ash falls that repeatedly interferedwith air traffic. The most powerful episode occurred on 3 December 2015 from the Voragine. After three further potent episodes fromthe Voragine, activity shifted to the NewSoutheast 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, thismultifaceted 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 themorphological 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.Published53-695V. Dinamica dei processi eruttivi e post-eruttiviJCR Journa

Reconstruction of the eruptive activity on the NE sector of Stromboli volcano: timing of flank eruptions since 15 ka

A multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka during the Vancori period, and has transitional compositional characteristics between the Vancori and Neostromboli phases. Roisa was followed by the San Vincenzo eruption that took place at ~12 ka during the early stage of Neostromboli period. The eruptive fissure of San Vincenzo gave rise to a large scoria cone located below the village of Stromboli, and generated a lava flow, most of which lies below sea level. Most of the flank eruptions outside the barren Sciara del Fuoco occurred in a short time, between ~9 and 7 ka during the Neostromboli period, when six eruptive events produced scoria cones, spatter ramparts and lava flows. The Neostromboli products belong to a potassic series (KS), and cluster in two differently evolved groups. After an eruptive pause of ~5,000 years, the most recent flank eruption involving the NE sector of the island occurred during the Recent Stromboli period with the formation of the large, highly K calc-alkaline lava flow field, named San Bartolo. The trend of eruptive fissures since 15 ka ranges from N30°E to N55°E, and corresponds to the magma intrusions radiating from the main feeding system of the volcano

Chemical heterogeneity of Mt. Etna magmas in the last 15 ka. Inferences on their mantle sources

Primitive basalticmagmas are crucial in the study of the geochemical heterogeneity documented in Etnamagmas and their inferred mantle sources. We undertook a systematic sampling of the less evolved basalts (Mg# N50) 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 ‘deepdyke 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, togetherwith 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–87Sr–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.Published123-1342V. Struttura e sistema di alimentazione dei vulcaniJCR Journa

The transition from summit to flank activity at Mt. Etna, Sicily (Italy): Inferences from the petrology of products erupted in 2007–2009

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 associatedwith lava flow emissions and lasting from a few weeks to months. Recent volcanic activity shows that, if there is a transition froman 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 themonitoring network of Mt. Etna.Wetherefore investigated the transition froma summit episodic eruption at SEC to flank activity utilizing a petrologic study of the products erupted from2007 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, themost significant episodes ofmagmarecharge 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 fromthe disruption of a foam layer at the top of the SEC reservoir which was rebuilt before each subsequent episode. The transition fromthe 2007–08 episodic eruption at SEC to the 2008–09 flank activitywas essentially triggered by the Sichuan earthquakewhich 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 activityPublished51-604V. Processi pre-eruttiviJCR Journa

Picturing Mt. Etna in the 18th century: a reconstruction from historical, stratigraphic and petrologic data of the 1763 flank eruptions

International audienceThe structure of an active volcano is highly dependent on the interplay among the geodynamic context, the tectonic assessment as well as the magmatic processes in the plumbing system. This complex scenario, widely explored at Etna during the last 40 years, is on the contrary incomplete for the recent historical activity. We focused on the activity that occurred in 1763 along the west flank of the volcano. Here, an eruption started on 6th February and formed the scoria cone of Mt. Nuovo and a roughly 4-km-long lava flow field. Another small scoria cone, known as Mt. Mezza Luna, is not dated in historical sources. It is located just 1 km eastward of Mt. Nuovo and produced a 700 m long flow field. The activity of Mts. Nuovo and Mezza Luna are intriguing to investigate for several reasons. First, the old geological maps and volcanological catalogues attribute Mt. Mezza Luna to the Mt. Nuovo eruption, while historical sources described Mt. Nuovo's activity as producing a single scoria cone and do not give information about the formation of Mt. Mezza Luna. Second, petrologic studies highlight that the products of Mt. Mezza Luna are similar to the sub-aphyric Etna basalts, which preserve a composition relatively close to Etna primitive magma and enable insights into the deep portion of the volcano's plumbing system. Third, the two scoria cones built up along the so-called West rift of Etna, which represents one of the main magma-intrusion zones of the volcano. Finally, La Montagnola eruption, which also occurred in 1763, along the South rift of the volcano, has been well-studied and provides useful information to be integrated with our data. We carried out a multidisciplinary study comprising a critical review of historical records, new field surveys, petrochemical analyses and petrologic modelling of the Mts. Nuovo and Mezzaluna eruptions and integrated our results with literature data. This multidisciplinary approach allowed improving the stratigraphic record of historical eruptions reported in the Mount Etna Geological map, modelling the sub-volcanic magmatic processes responsible for magma differentiation and speculating on possible inferences with the volcano tectonics of the area

Geochemical pattern classification of recent volcanic products from Mt. Etna, Italy, based on Kohonen maps and fuzzy clustering

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 episodesPublished1151-11645V. Dinamica dei processi eruttivi e post-eruttiviJCR Journa

Geochemical Patterns Classification of recent Mt. Etna volcanic products based on a synopsis of Kohonen Maps and Fuzzy Clustering

During the last two decades Mt. Etna experienced many summit and flank eruptions with different styles of activity, ranging from quiet lava effusion to explosive activity consisting of Strombolian explosions and/or spectacular fire fountains. This complex picture entails the presence of a complex plumbing system where magma dynamics strongly controls both the eruptive style and magma differentiation. All these eruptive events have furnished volcanic products on which systematic petrographic and geochemical analyses have been carried out since the mid 1990s. In particular, the content of major and trace elements of lavas is a key-point to characterize the composition of a magma emitted during an eruption. Petrologic investigations are traditionally based on the interpretation of compositional patterns described by selected oxides and/or elements in binary and ternary petrologic systems. This kind of analysis provides useful information about the magmatic processes occurring in the plumbing system. In this presentation we investigate whether the quality of petrologic investigations is improved by the application of more sophisticated analytical techniques based on the use of a relatively large number of parameters. To this purpose, we selected 13 components, i.e., SiO2, K2O, CaO/Al2O3, Mg#, Th, La, Nb, Nd, Sr, Tb, Cr, Ni and Rb/Nb. This choice brings along the problem of designing a suitable statistics and a convenient visualization of the results. As a way out, we propose advanced concepts of multivariate classification based on a synopsis of Kohonen Maps and Fuzzy Clustering, and apply them to the study of volcanics erupted from Mt. Etna between 1995 and 2005. Lavas erupted during the fire fountains (in 2000) and during the flank eruptions (2001, 2002-03) represent the most primitive products erupted from Mt. Etna in the investigated period. The literature data suggest that during the 2001 and 2002-03 eruptions two magmas with different geochemical characteristics were contemporaneously erupted. One magma type ascended from a deep portion of the plumbing system (> 5 km), and was emitted from the so called “Lower” (2001) and “Southern” vents (2002-03). Another one rose from a shallower reservoir (<5 km) and was erupted from the so called “Upper” (in 2001) and “Northern” vents (in 2002-03). In our analysis the “Lower” and “Southern” vent lavas are assigned to the same cluster ID and are grouped together also in the Kohonen Map. On the other hand, “Upper” vent lavas and “Northern “ vent lavas are clearly distinguished from each other as well as from the afore mentioned products. Volcanics emitted by the South-East crater during the fire fountains in 2000 belong to the same fuzzy cluster as the “Lower” and “Southern” vent lavas, however, a neat distinction with respect to 2001 and 2002-03 lavas becomes evident in the Kohonen Map. Besides this we observe differences in the seismic signal characteristics between the fire fountain events and flank eruptions, supporting the hypothesis that various eruptive sources were active on Mt Etna in 2000, 2001 and 2002-03. The relation of the products to eruptive sources is less clear in the time span between 1995 and 1999, when essentially only the summit craters were active.PublishedVienna, Austria1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attiveope

New Insights into Composition of Volcanic Products at Mt. Etna, Italy, from Geochemical Pattern Classification

Geochemical analyses of volcanic products erupted by Mt. Etna, Italy, have been carried out by INGV-CT (formerly CNR-IIV) staff since three decades. The need to realize a near-real time monitoring of the basic compositional features of a magma compelled since the 1990s an organization of personnel engaged for sampling and analyzing the collected rocks in laboratories. Geochemical monitoring has been outstandingly improved with the application of sophisticated, but quick, analytical techniques which take into account both oxides as well as trace elements of lavas. The geochemical monitoring offers up-to-date information on processes and dynamics of magma, and allows documenting the evolution of different eruptive styles throughout an eruptive event. Accordingly, changes in chemical parameters have become a key information for the Italian Civil Defence to highlight any hazardous evolution of volcanic activity at Etna, and promptly warn potential endangered populations. Compared to traditional classification methods, where compositional patterns are defined by selecting oxides and/or elements in binary and ternary petrologic systems, we can handle a statistics with many components, in our specific case thirteen (SiO2, K2O, CaO/ Al2O3, Mg, Th, La, Nb, Nd, Sr, Tb, Cr, Ni, Rb/Nb). The statistical treatment of geochemical patterns exploits Kohonen Maps and Fuzzy Clustering, which are applied to samples collected at Etna between 1995 and 2005. We present a comprehensive picture of the evolution of these products in time and space with a convenient visualization of the results. The application of multivariate classification allows us to identify a signature in the compositional characteristics of magma erupted from the four summit craters and/or flank eruptive vents, even in the time spans in which volcanic activity was concurrent. Dubious compositional changes are also considered in the light of earthquakes and volcanic tremor characteristics, which offer independent evidence of the significance of the results