The integration of surface geological observations and geophysical data acquired in real time can enable a more reliable reconstruction of the propagation and arrest phases of magmatic intrusions, improving the assessment of eruptive scenarios associated with lateral intrusions at Etna, among the most dangerous phenomena for the communities living on the volcano's slopes. This is the finding of a study by researchers at INGV, published in the scientific journal Frontiers in Earth Sciences, which reconstructs what occurred on Europe's highest active volcano on May 13, 2008, when it was possible to simultaneously observe the processes developing at the surface and at depth during a magmatic intrusion — that is, the ascent of magma within the volcano along rock fractures, without it necessarily reaching the surface in an eruption.
On that date, a lateral dyke — a body of magma that infiltrates along a rock fissure — began propagating from the volcano's central feeding conduit toward the north, generating an extensive field of surface fractures and a sequence of earthquakes that accompanied its advance, precisely tracing its migration. The magma did not reach the surface on the northern flank: the propagation changed direction toward the south, giving rise to the eruption in the Valle del Bove.
"The initial dynamics caused particular concern because they were reminiscent of the scenario of March 1981, when an eruptive fissure rapidly propagated toward Randazzo, causing serious damage," says Alessandro Bonaccorso, an INGV director. "In 2008, however, it stopped spontaneously, offering a unique scientific opportunity to observe the behavior of a lateral intrusion in detail." "We estimated that the magma propagated to a depth of between approximately 200 and 600 meters," explains Marco Neri, an INGV director, "and that, as the dyke advanced, the magma pressure was no longer sufficient to overcome the resistance of the rock into which it was intruding. Its propagation thus slowed until it stopped, while the magma gradually began to solidify."
"The cumulative seismic moment released during the event," say Elisabetta Giampiccolo and Carla Musumeci, seismologists at INGV, "coincides with the elastic energy expected from the modelled dyke. This data, combined with other findings, indicates that the system had exhausted its propagation 'energy budget': no residual energy, no possibility of advancing further."
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