Description: Basaltic volcanoes constitute a big portion of the active volcanoes worldwide and their explosive activity, generally accompanied by eruptive columns formation and pyroclastic fallouts, produced, in the last decades, several damages on human’s life with great economical and aviation impact (Scollo et al., 2009; Bonaccorso et al., 2011). Is therefore not surprising the flourishing number of studies devoted to the investigation of the link between plumbing system dynamics and eruptive style. Basaltic eruptive activity may range in a widespread spectrum from lava effusion up to rare violent Plinian eruptions. However, the most iconic explosive activities of basaltic volcanoes are represented by Strombolian explosions and lava fountains. From 2000 to 2013 several were the episodic lava fountain eruptions taking place at South-East Crater and New South-East Crater (SEC and NSEC – Mt. Etna, Italy –) and a similar eruptive pattern (with gradual increase in explosivity marked by the passage from strombolian to fountain activity) was observed in almost all explosive events. To justify the onset, periodicity and the transition between the above-mentioned eruptive styles, different hypothesis on the degassing dynamics have been made. Here, we make use of a laboratory volcano, Mt. Etna, to test the validity of these assumptions and to calculate different volcanological parameters (e.g. erupted volume and gas flux in the plumbing system). In particular, we applied the Collapsing Foam layer (CF) model (Jaupart and Vergniolle, 1989) to the episodic lava-fountains eruptions occurred at the SEC-NSEC volcanic system between 2000 and 2013. First, we test the validity of CF model by studying the exceptional series of lava fountains observed in 2000 at SEC, with a multi-parametric approach and by assuming the CF model as the reference source model for this eruption, looking for the best parameters that allows to fit the observed pattern and eruptive behavior (e.g. intermittence time, erupted volume of lavas etc.). Secondly, we apply the CF model to three selected eruptions that took place at Mt. Etna south-eastern vents between 2000 and 2013 (the 2000, 2007-08 and 2011-13 eruptions).

Description: Published

Description: Parma

Description: 5V. Processi eruttivi e post-eruttivi

Description: Basaltic volcanoes represent a very large portion of active volcanism and exhibit a wide variability in their eruptive style. The basaltic eruptive activity in fact shows either a purely effusive behavior or an explosive character, which can, rarely, also turn into violent Plinian eruptions. The most characteristic explosive activities of basaltic magmatism are represented by Strombolian eruptions and lava fountains. The study of the relationship that exists between the pre-eruptive dynamics (e.g. fractional crystallization, mixing, degassing), the chemicalphysical variations of the magma in the volcanic feeding system and the related outcomes (in terms of eruptive style and geophysical markers) at the surface has been, in the last decades, reason of numerous studies. Nonetheless, the complexity of the volcanic system and its inaccessibility to direct observations still makes it difficult to reconstruct the dynamics of the magmatic system, basing on surface observations of the eruptive activity. A challenging objective of modern volcanology is to quantitatively characterize eruptive/degassing regimes from geophysical signals (in particular seismic and infrasonic), for both research and monitoring purposes. The outcomes of the attempts made so far are still considered very uncertain because volcanoes remain inaccessible when deriving quantitative information on crucial parameters such as plumbing system geometry and magma viscosity. Therefore the realization of laboratory made by several devices, capable to scale and reproduce in a controlled way the degassing dynamics of volcanic systems and measure the relative elastic markers (seismic and acoustic), is an indispensable tool to identify reliable quantitative relationships between the geophysical signals and the related eruptive and outgassing parameters. With the Aeolus project we build an experimental laboratory for the study of degassing dynamics through analogue volcanic eruptions. In particular the laboratory is capable of 1) investigate the relationship between degassing processes and the relative seismo-acoustic signals; 2) study the effect of different degrees of irregularity (i.e. roughness of the internal surface) of volcanic conduits on the eruptive style and/or the associated seismic-acoustic signals; 3) unravel the timescales of cyclic activity at basaltic volcanoes, reproducing the foam collapse model of Jaupart and Vergniolle (1988, 1989), which explains the transition between different explosive terms of the basaltic system (e.g. Strombolian activity and lava fountains), in a range of dimensionless parameters close to the volcanic system.

Description: Published

Description: Parma

Description: 4V. Processi pre-eruttivi

Description: 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.

Description: Published

Description: 33

Description: OSV2: Complessità dei processi vulcanici: approcci multidisciplinari e multiparametrici

Description: JCR Journal