Understanding the nature of pyroclastic flows, one of the most dangerous phenomena that can occur in the summit areas of Etna. This is the aim of the research, signed by INGV, published in the Journal of Volcanology and Geothermal Research
Reconstruct the dynamics of the pyroclastic flow of February 11, 2014 with the future aim of evaluating the potential danger of Etna's pyroclastic flows, thus reducing the risks for scientists and tourists who visit the summit of one of the most active volcanoes in the world every year world. This is the study conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV). The research, funded by the Civil Protection Department (DPC), analyzed the collapse of a portion of the New Southeast Crater that occurred on February 11, 2014, which generated a pyroclastic flow that spread very rapidly towards the Valle del Bove.
The study of volcanic deposits has provided scientific data on the possible triggering and dynamics of the pyroclastic flow generated at Etna, and has constituted a first useful element for risk assessment also in other similar volcanoes. The research was published in the Journal of Volcanology and Geothermal Research (Link).
"Until a few decades ago", explains Daniele Andronico, volcanologist of the Etna Observatory (INGV-OE), "since Etna was not inclined to generate pyroclastic flows, lava flows were considered among the most dangerous volcanic phenomena for their potential threat to population centers. After 1998, however, over 200 paroxysmal events, characterized by lava fountains and lava flows, generated the rapid growth in the summit area of the Southeast Crater and, starting from 2011, of the New Southeast Crater".
The continuous morphological variations of these two cones and, in particular, of their flanks, formed by the overlapping of ash and lava scoria, have generated a situation of potential instability on the slopes, especially the one facing east and close to the edge of the very steep wall of the Bove Valley.
“Pyroclastic flows”, continue Alessio Di Roberto and Emanuela De Beni, INGV researchers and co-authors of the study, “are largely unpredictable. They involve very hot materials and can reach considerable distances from the point of detachment”. The unpredictability of these phenomena, in the specific case of volcanoes such as Etna, must be related to the uncertainty about the possibility of their occurrence, the trigger mechanisms and the areas of possible invasion. Therefore, it becomes essential to reconstruct the possible predisposing factors for the generation of these phenomena and to model their propagation.
Several factors favored the 2014 event: the rapid growth of a large cone (the New Southeast Crater) on the edge of the Valle del Bove, the Strombolian explosive activity and the presence of lava flows assets that have overloaded the flanks of the cone. The presence of effusive vents, fractures and hot gases have also contributed to mechanically and thermally weakening the cone, making it unstable and prone to collapse. The last cause of the collapse, although not least, was the thrust of a body of magma intruded at a shallow depth. This intrusion triggered the final destabilization of the cone, the failure of which actually generated the pyroclastic flow along the steep sides of the cone, with more than 30° of inclination.
"The numerical simulation of the propagation of the pyroclastic flows of the 2014 eruption, as well as other likely scenarios, on which we are still working, will help to better evaluate the danger associated with these phenomena and therefore to mitigate the risks to which scientists may be exposed and tourists who visit the summit areas of Etna”, concludes Andronico.
The published research has an essentially scientific value, without immediate implications regarding the aspects of civil protection at the moment.
Figure 1 - Images recorded by INGV-OE surveillance cameras (visible and thermal). The sequence shows the detachment of volcaniclastic material (consisting of fragments of lava and pyroclastics) from the flank of the New Southeast Crater, which generates a pyroclastic flow along the flank of the cone, which spread to the base of Valle del Bove. Also visible is an ash cloud formed by the fragmentation of hot material which remains suspended up to about 1 km above the Valle del Bove even after the flow has stopped
Figure 2 - The ash cloud produced by the pyroclastic flow that descends from the flank of the New Southeast Crater. Photo taken a few minutes after the event by Toti Domina, from the Casa di Paglia Felcerossa, on the eastern side of the Etna Park (900 m asl) near the hamlet of Fornazzo (Milo)
Figure 3 - Deposits of the pyroclastic flow of 11 February 2014 at Etna, measured along the western wall of the Valle del Bove. Left: panoramic view of the depot; right: detail of the deposit showing the presence of several stratigraphic units of flow, superimposed on ash and lapilli erupted in 2013
Figure 4 - The images show the authors of the publication while carrying out the surveys inside the Valle del Bove
Abstract
“Pyroclastic density currents at Etna volcano, Italy: The 11 February 2014 case study”, whose authors are a group of researchers from the INGV sections of Catania and Pisa (Andronico, D., Di Roberto, A., De Beni, E. , Behncke, B., Bertagnini, A., Del Carlo, P., Pompilio, M.)
On 11 February 2014, a considerable volume (0.82 to 1.29 × 106m3) of unstable and hot rocks detached from the lower–eastern flank of the New Southeast Crater (NSEC) at Mt. Etna, producing a pyroclastic density current (PDC). This event was by far the most extensive ever recorded at Mt. Etna since 1999 and has attracted the attention of the scientific community and civil protection to this type of volcanic phenomena, usually occurring without any clear volcanological precursor and especially toward the mechanisms which led to the crater collapse, the PDC flow dynamics and the related volcanic hazard. We present here the results of the investigation carried out on the 11 February 2014 collapse and PDC events; data were obtained through a multidisciplinary approach which includes the analysis of photograph, images from visible and thermal surveillance cameras, and the detailed stratigraphic, textural and petrographic investigations of the PDC deposits. Results suggest that the collapse and consequent PDC was the result of a progressive thermal and mechanical weakening of the cone by repeated surges of magma passing through it during the eruptive activity prior to the 11 February 2014 events, as well as pervasive heating and corrosion by volcanic gas. The collapse of the lower portion of the NSEC was followed by the formation of a relatively hot (up to 750 °C) dense flow which traveled about 2.3 km from the source, stopping shortly after the break of the slope and emplacing the main body of the deposit which ranges between 0.39 and 0.92 × 106 m3. This flow was accompanied by a relatively hot cloud of fine ash that dispersed over a wider area. The results presented may contribute to the understanding of this very complex type of volcanic phenomena at Mt. Etna and in similar volcanic settings of the world. In addition, results will lay the basis for the modeling of crater collapse and related PDC events and consequently for the planning of hazard assessment strategies aimed at reducing the potential risks to scientists and tens of thousands of tourists visiting Etna's summit areas every year.