With a study conducted by INGV and OGS, reconstructed the possible structural conditions that in Etna have allowed the transfer of magma from the depths to the surface
The area in which Etna rises and the adjacent submerged areas are characterized by the presence of "transcurrent" faults (i.e. with a horizontal movement) on a regional scale, whose activity and interaction has created the conditions for the transfer of magma from the depths up to the surface. This is what emerges from a study conducted by a group of researchers from the National Institute of Geophysics and Volcanology (INGV) and the National Institute of Oceanography and Experimental Geophysics (OGS), just published in the journal "Scientific Reports" by Nature.
"Starting at least 500.000 years ago", explains Marco Firetto Carlino, INGV researcher and first author of the article, "the tectonic activity of a large fault zone in the southern part of the volcano (between Acireale and the surroundings of Adrano) has led to the formation of "opening" zones in the earth's crust. These represented the preferential routes for the ascent of the magmas emitted through eruptive fissures spread along the fault. These fissures have been identified between Aci Trezza and Adrano and characterize the early stages of Etna activity. The continuous strike-slip deformation along the same fault zone and, subsequently, also along other zones further north, as well as their mutual interaction, led to the migration of volcanism and, at the same time, to the sudden closure of the previously active eruptive conduits. This phenomenon explains the process of migration of volcanism from the southern slope (active from at least 500.000 to about 200.000 years ago), up to the Valle del Bove area (from about 100.000 to 70.000 years ago) and to the current eruptive centers (from about 60.000 years ago to today).
Understanding the mechanisms through which magma is transferred through the crust to the surface and, therefore, investigating the relationships between tectonics and volcanism in an area also affected by high seismicity, falls within the main competences of INGV.
Starting from 2014, in fact, the Etna Observatory of the Institute (OE-INGV) has undertaken an activity of acquisition, processing and interpretation of images of the earth's crust, obtained through the analysis and the relationship between high resolution seismic data , magnetic and gravimetric data, acquired off the volcano Etna. This multidisciplinary approach has allowed us to investigate, with a detail never achieved before, the submerged portions of the south-eastern slope of Etna, where the most ancient volcanic manifestations have been found. Precisely this slope represents a key area for understanding the evolution in space and time of volcanism in this region.
"The deformation phenomena linked to strike-slip tectonics have not only determined the Etna volcanism and its distribution in space and time", adds Firetto Carlino, "but have also determined the formation and activity of the active tectonic structures affecting the eastern slope of Etna, characterized by high seismicity, even recent (remember, for example, the earthquake of magnitude Mw 4.9 of 26 December 2018 which affected the town of Fleri and the surrounding areas), and by an important phenomenon of gravitational sideslip. The latter appears to be closely influenced by the structural configuration of the volcano's basement, deeply deformed by the fault system recognized in this work”, concludes the researcher.
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Image - Schematic model illustrating the evolution in space and time of the Etna volcanism, guided by a strike-slip tectonics, controlled by the regional stress field shown in the center of the image (T: opening; S: shortening; Hmax: axis of maximum horizontal stress). (a): starting from at least 500.000 years ago, the activity of a large strike-slip fault zone ("Southern Etna Shear Zone") has created zones of local crustal extension (releasing zones), preferential routes for ascent of the magmas. The continuous deformation along the "Southern Etna Shear Zone" and, subsequently, along further zones of transience propagated further north (eg "Central Etna Shear Zone"), as well as their mutual interaction have led to the migration of volcanism along the southern slope and in the Valle del Bove area (bec), up to the current eruptive centers (d). The migration of the areas in relaxation, and therefore of the volcanism, was associated with the sudden closure of the previously active eruptive conduits through phenomena of local positive tectonic inversion (so-called transpression).