The 3 July 2019 paroxysm at Stromboli volcano (Italy): is Stromboli playing by new rules?

On the afternoon of 3 July 2019, a violent explosive event (called paroxysm) affected the entire crater terrace of Stromboli volcano in Southern Italy, generating two pyroclastic flows that advanced for about 1 km across the sea beyond the coastline. The eruptive column rose for about 4 km above the summit and was accompanied by intense fall of scoriae and pumice, mostly around the village of Ginostra in the southwestern sector of the volcano, setting the vegetation on fire and causing one fatality and one injured person. The death toll could have been much higher, considering that during the summer months there are hundreds of tourists climbing the volcano every evening. In fact, on the afternoon of 3 July 2019 there were 230 people waiting to start their climb.

Stromboli is well-known as the lighthouse of the Mediterranean for its persistent "normal" Strombolian activity, consisting of low-energy explosions occurring every 10-20 minutes from multiple vents located in the crater area. This persistent activity is accompanied by lava flows at intervals of several years and, occasionally, is interrupted by discrete violent explosive events, such as the one that occurred on 3 July, which lasted several minutes, fed a km-long vertical column of gas, scoria and pumice that launched blocks up to 2-3 km from the source. In the last century there have been about 17 paroxysms with the strongest one, also associated with a tsunami, on 11 September 1930, and the most recent ones on 5 April 2003 and 15 March 2007.

Paroxysms are sudden, infrequent and highly damaging events that are very difficult to forecast. Previous work at Stromboli has shown that each of the last 4 paroxysms over 70 years of recorded eruptive history were preceded by lava effusion. In particular, the two most recent paroxysms in 2003 and 2007 occurred after the effusion of a similar cumulative volume of lava over a period of a few weeks to months preceding the large explosive events. These considerations have led to the current hypothesis that the volume of the effusive activity can be used to forecast future paroxysmal events. However, the 3 July 2019 did not play by this rule; it was preceded by very limited effusive activity only two minutes before the explosive event. At the same time, and rather untypical for the most recent activity of Stromboli, effusive activity started immediately after the explosive event, accompanied by intense explosive activity, and is still ongoing at the time of writing (early August 2019), raising concerns about the possibility of a second paroxysm.

It is clear that in order to enhance our ability to forecast such deadly events, it is crucial to understand their driving mechanisms. We propose to exploit this unique opportunity to capitalise on this unexpected event on 3 July 2019 through a detailed petrological and geochemical investigation of the eruptive products to unravel pre- and syn-eruptive magma ascent and degassing processes and their timescales, magma storage and crystallisation conditions as well as magma mixing processes and their timescales prior to eruption.

This is a unique opportunity to obtain, for the first time, crucial and novel information on the processes and timescales of magma ascent and degassing of such a disruptive event using the solid eruptive products that directly probe the underlying magma plumbing system. As the clock on the short-lived radionuclide 210Po (half-life = 138 days), which is one of our probes for determining the timescales of magma ascent and gas transfer, is already ticking, funding this proposal is time-critical.

Volcanic eruptions fascinate and frighten at the same time. If an unexpected large deadly eruption occurs at a perceived "trustworthy" volcano, which also happens to be a renowned touristic place, such as Stromboli, the impact is even higher. During a large-scale eruptive event such as the one that occurred on 3 July 2019 at Stromboli, there are many stories to be told: personal (i.e., people living on Stromboli and the tourists visiting the island), official (i.e., local authorities), scientific (i.e., scientists monitoring the volcano) and hidden (i.e., what actually happens inside the volcano's underlying magmatic system). Working with local authorities, local communities and the many scientists monitoring the volcano, we will capitalise on our expertise to convey the findings from this study telling the hidden story, i.e., the magmatic perspective, of the 3 July 2019 paroxysm of the volcano.

We will engage with: 1) the local communities and civil authorities on Stromboli and the Aeolian Islands, via our personal contacts and experience (PI Petrone, CoI Gertisser, PPs Scarlato and Mollo have decadal experience working on Italian volcanoes); 2) the Italian Civil Protection via direct contact trough INGV (PP Scarlato), which is the reference scientific institution for geo-hazards of the Italian government; 3) the volcanological guides who regularly run touristic tours to the top of Stromboli volcano; (4) schools in the UK and Italy, via personal contacts of the PI, CoI and PPs, to inspire the next generation of scientists and to raise awareness of natural hazards; 5) National geological institutions and volcano observatories, via direct contact and the preferential access of INGV to the international network of volcano observatories and volcanic centres; 6) the general public, particularly those visiting the Natural History Museum (> 5 million a year).

We will engage the above-mentioned beneficiaries in different ways, from the more traditional, like direct meetings, public talks, social media, blog, TV and Radio interviews, to more focused workshops in schools. In fact, PI Petrone has established contacts with the William Perkin School in London, which has a strong scientific focus, to develop a long-term program of regular lectures and hands-on activities that will follow the progress of the project. CoI Gertisser runs learning and outreach activities using Keele's STARDOME (owned and managed by Higher Horizons+) allowing an IMAX-type movie experience for students on "Supervolcanoes". It can be brought into schools and can accommodate 25 pupils during a 30-minute session. We expect that this program can have long lasting impact promoting STEM subjects at schools in the UK.

The proposed project falls within the remit of NERC strategy addressing two societal challenges: 1) managing environmental change and 2) resilience to environmental hazard strands.