A team of researchers from the INGV has integrated geological and seismological data to reconstruct one of the most significant episodes of magma propagation within a volcano.
A new study conducted by a team of researchers from theIstituto Nazionale di Geofisica e Vulcanologia (INGV) reconstructs what happened on Etna on May 13, 2008, when it was possible to observe simultaneously the processes that develop on the surface and at depth during a magmatic intrusion, that is, the rise of magma inside the volcano along fractures in the rock, without necessarily reaching the surface due to an eruption. The study, entitled "The 2008 Mt. Etna dike arrest: integration of structural investigation, seismic and energy-balance analysis”, was recently published in the scientific journal Frontiers in Earth Sciences.
On that date a lateral dike, that is, a body of magma that insinuates itself along a crack in the rock, began to spread from the volcano's central feeder pipe towards the north, generating an extensive surface fracture field and a sequence of earthquakes which accompanied its advance, precisely tracing its migration. The magma did not reach the surface on the northern flank: the propagation changed direction towards the south, giving rise to the eruption in the Valle del Bove. On the ground remained a “dry” fracture field, i.e. non-eruptive, one of the most significant cases of interaction between a magmatic intrusion and brittle ground deformation.
"The initial dynamics caused particular concern because the direction of the dike recalled the scenario of March 1981, when an eruptive fissure rapidly spread towards Randazzo causing serious damage. - he declares Alessandro Bonaccorso, Research Director of INGV and coordinator of the study - In 2008, however, the propagation stopped spontaneously, offering a unique scientific opportunity to observe in detail the behavior of a lateral intrusion.".
The analysis of surface fractures and seismic data allowed us to reconstruct the evolution of the intrusion.We estimated that the magma propagated to a depth of between approximately 200 and 600 metres - explains Marco Neri, Research Director at INGV and co-author of the article - The study also shows that, as the dyke advanced, the magma's pressure was no longer sufficient to overcome the resistance of the rock it was intruding into. Its propagation thus slowed until it stopped, while the magma gradually began to solidify.".
“The cumulative seismic moment released during the event - they declare Elizabeth Giampiccolo e Carla Musumeci, seismologists from the INGV team that conducted the study - coincides with the elastic energy expected from the modeled dike. This data, combined with the change from extensional to compressional failure mechanisms that generate earthquakes during the dike's propagation, indicates that the system had exhausted its propagation 'energy budget': no residual energy, no possibility of further advance. The convergence of surface fractures, hypocentral migration, evolution of focal mechanisms, and energy balance made the May 13, 2008, event a unique example for understanding Etna's lateral intrusions.
The study demonstrates that integrating surface geological observations with real-time geophysical data can enable a more reliable reconstruction of the propagation and arrest phases of magmatic intrusions, improving the assessment of eruptive scenarios associated with Etna's lateral intrusions, among the most dangerous phenomena for the communities living on the volcano's slopes.
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Figure 1 - Map and field observations relating to the May 13, 2008, dyke intrusion along the Northeast Rift of Etna (a). The topographic map highlights the dike's propagation direction toward Randazzo, the arrest area, the eruptive fissure, and the 2008 and post-1971 lava flows. The surface fracture lines, solid or dashed where uncertain, show the deformation induced by the intrusion. The photographs (b, c) document open fractures on the ground with metric amplitude, while the rose diagram (d) summarizes the structural orientation of the fractures measured in the field (Modified from Bonaccorso et al., 2026).
Figure 2 – 3D schematic diagram of the May 13, 2008, magmatic intrusion on the northern flank of Etna. The dike, rising to a depth of 200–600 m, generated shallow, "dry" fractures north of the Northeast Crater, while southward propagation fueled the eruption in the Valle del Bove. Focal mechanisms show a transition from an extensional to a compressional regime, indicating the intrusion's cessation.
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