Variable Magnitude and Intensity of Strombolian Explosions: Focus on the Eruptive Processes for a First Classification Scheme for Stromboli Volcano (Italy)

Alessandro Bonaccorso,Giovanni Macedonio,Sonia Calvari,Nicola Casagli,Federico Di Traglia,Flora Giudicepietro

doi:10.3390/rs13050944

Abstract

Strombolian activity varies in magnitude and intensity and may evolve into a threat for the local populations living on volcanoes with persistent or semi-persistent activity. A key example comes from the activity of Stromboli volcano (Italy). The “ordinary” Strombolian activity, consisting in intermittent ejection of bombs and lapilli around the eruptive vents, is sometimes interrupted by high-energy explosive events (locally called major or paroxysmal explosions), which can affect very large areas. Recently, the 3 July 2019 explosive paroxysm at Stromboli volcano caused serious concerns in the local population and media, having killed one tourist while hiking on the volcano. Major explosions, albeit not endangering inhabited areas, often produce a fallout of bombs and lapilli in zones frequented by tourists. Despite this, the classification of Strombolian explosions on the basis of their intensity derives from measurements that are not always replicable (i.e., field surveys). Hence the need for a fast, objective and quantitative classification of explosive activity. Here, we use images of the monitoring camera network, seismicity and ground deformation data, to characterize and distinguish paroxysms, impacting the whole island, from major explosions, that affect the summit of the volcano above 500 m elevation, and from the persistent, mild explosive activity that normally has no impact on the local population. This analysis comprises 12 explosive events occurring at Stromboli after 25 June 2019 and is updated to 6 December 2020.

Highlights

Strombolian activity is characterized by explosive transients of variable intensity, from pyroclast-free gas explosions to intense explosions, with the formation of a few-km-high eruptive columns, ballistic ejection, and occasional generation of pyroclastic density currents [1,2,3,4,5,6]
Monitoring camera network, integrated with geophysical data from the Istituto Nazionale di Geofisica e Vulcanologia (INGV) seismic network, as well as the ground deformations obtained from different remote sensing and geodetic techniques
We describe here the 12 explosive events analysed in this paper on the basis of information gathered from the INGV weekly reports (Table 3) integrated with the analysis of the images recorded by the INGV monitoring webcams (Table 4)

Summary

Introduction

Strombolian activity is characterized by explosive transients of variable intensity, from pyroclast-free gas explosions (puffing) to intense explosions, with the formation of a few-km-high eruptive columns, ballistic ejection, and occasional generation of pyroclastic density currents [1,2,3,4,5,6]. Archipelago volcanic arc in the south Tyrrhenian Sea (Figure 1a) It is 924 m high above sea level (a.s.l.; Figure 1b) and extends below the sea down to ~2000 m depth, reaching a total elevation of ~3000 m [10]. Explosions occur from vents located within the summit crater terrace depression at ~750 m elevation (Figure 1c), which is ~ 300 m long in a NE-SW direction, ~50 m wide and ~50 m deep (Figure 1c). Three crater areas are located within the summit depression: the NE crater zone (NEC), the Central crater zone (CC) and the SW crater zone (SWC), each of them comprising a variable number of active vents (Figure 1c)

Methods

Results

Discussion

Conclusion