Space‐Time Evolution of Magma Storage and Transfer at Mt. Etna Volcano (Italy): The 2015–2016 Reawakening of Voragine Crater

Abstract

The eruptions of December 2015 and May 2016 at Voragine crater were among the most explosive recorded during the last two decades at Mt. Etna volcano. Here we present data coming from geophysics (infrasound, LP, VLP, volcanic tremor, VT earthquakes, and ground deformations) and petrology (textural and microanalytical data on plagioclase and olivine crystals) to investigate the preeruptive magma storage and transfer dynamics leading to these exceptional explosive eruptions. Integration of all the available data has led us to constrain chemically, physically, and kinetically the environments where magmas were stored before the eruption, and how they have interacted during the transfer en‐route to the surface. Although the evolution and behavior of volcanic phenomena at the surface was rather similar, some differences in storage and transfer dynamics were observed for 2015 and 2016 eruptions. Specifically, the 2015 eruptions have been fed by magmas stored at shallow levels that were pushed upward as a response of magma injections from deeper environments, whereas evidence of chemical interaction between shallow and deep magmatic environments becomes more prominent during the 2016 eruptions. Main findings evidence the activation of magmatic environments deeper than those generally observed for other recent Etnean eruptions, with involvement of deep basic magmas that were brought to shallow crustal levels in very short time scales (∼1 month). The fast transfer from the deepest levels of the plumbing system of basic, undegassed magmas might be viewed as the crucial triggering factor leading to development of exceptionally violent volcanic phenomena even with only basic magma involved.

Coupled Short- and Medium-Term Geophysical Signals at Etna Volcano: Using Deformation and Strain to Infer Magmatic Processes From 2009 to 2017

“…Comparing with data recorded for the NSEC lava fountains, this result suggests that eruptions through VOR are sourced from a deeper portion of the magmatic plumbing system. This evidence agrees with petrological data that show the activation of magmatic environments deeper than those generally observed for other recent Etnean eruptions, involving deep basic magmas brought to shallow crustal levels in very short time scales (Cannata et al, 2018). Particularly, the olivine populations and (2a) is the zone comprising the sources of the recharging phases (inflation) whose centroid is indicated with the lower star; (2b) is the zone comprising the sources of the eruptive discharging phases (deflation) whose centroid is indicated with the upper star.…”

“…This allowed a more complete and robust representation of the different sources that acted during the different recharging (i.e., medium-term preparatory phases) and discharging (i.e., the eruptive phases) phases. We highlight and discuss how the inferred sources are in agreement with a recent conceptual model of the Etnean plumbing system, made up of different magma storage zones, which were constrained by petrological and geochemistry studies (i.e., Kahl et al, 2015;Cannata et al, 2018). To the best of our knowledge, this is the first study where results from GPS and borehole strain-meter networks are used together to investigate medium-and short-term deformation sources at Etna volcano.…”

“…. Regarding the four events that involved the VOR crater during the first days of December 2015, both Aloisi et al (2017) and Cannata et al (2018) found that the recorded deformation pattern is compatible with a deflation source located under the crater, at a depth of ∼5 km b.s.l. Comparing with data recorded for the NSEC lava fountains, this result suggests that eruptions through VOR are sourced from a deeper portion of the magmatic plumbing system.…”

“…Furthermore, there is a general agreement that this border zone is coincident with the pathway that the magma takes toward the surface (e.g., Bonforte et al, 2008). Along this pathway, the magma can store and differentiate at various depths, forming a multilevel plumbing system characterized by several magmatic environments, where different types of olivines can form (e.g., Kahl et al, 2015;Cannata et al, 2018). Thanks to the uniform approach of modeling applied here, for the inflation/deflation phases modeled by GPS data in the investigated period, our results highlight a very clear separation in depth between the inflation and the deflation sources (Figure 7).…”

“…(3) Shallow storage feeding the lava fountain episodes of NSEC inferred by strain changes recorded by borehole strain-meters. The positions of the centroid of the modeled sources 2a, 2b and 3 are coincident with the different levels of the magmatic environments constrained by Cannata et al (2018) by petrological data. In the section the seismic velocity estimated by Aloisi et al (2002) is also shown.…”