Abstract
In 2019, Stromboli volcano experienced one of the most violent eruptive crises in the last hundred years. Two paroxysmal explosions interrupted the ‘normal’ mild explosive activity during the tourist season. Here we integrate visual and field observations, textural and chemical data of eruptive products, and numerical simulations to analyze the eruptive patterns leading to the paroxysmal explosions. Heralded by 24 days of intensified normal activity and 45 min of lava outpouring, on 3 July a paroxysm ejected ~6 × 107 kg of bombs, lapilli and ash up to 6 km high, damaging the monitoring network and falling towards SW on the inhabited areas. Intensified activity continued until the less energetic, 28 August paroxysm, which dispersed tephra mainly towards NE. We argue that all paroxysms at Stromboli share a common pre-eruptive weeks-to months-long unrest phase, marking the perturbation of the magmatic system. Our analysis points to an urgent implementation of volcanic monitoring at Stromboli to detect such long-term precursors.
Highlights
In 2019, Stromboli volcano experienced one of the most violent eruptive crises in the last hundred years
No monitoring system existed on the volcano until after the early Nineties, and the only other paroxysmal explosions studied with modern volcanological tools occurred on 5 April 2003 and 15 March 2007
Paroxysmal events pose an evident hazard for the inhabited areas, as they erupt more material (>104 m3 in volume) to greater heights (>3 km above the vents), with volcanic ballistic projectiles ejected to distances of 1–3 km radially outward, and tephra covering the coastline and beyond[4]
Summary
01/06 08/06 15/06 22/06 29/06 06/07 13/07 20/07 27/07 03/08 10/08 17/08 24/08 31/08 07/09 14/09 21/09 28/09 all NS SCS time. The normal activity typically erupts crystal-rich (45–55 vol.%), black scoriaceous products, fed by a shallow, outgassed highly porphyritic (HP) basaltic magma residing at depths within about 2–4 km[10,11,12,13]. The magnitude of explosions scales with the mass and separation depth of gas from the magma source involved, with no physicallybased thresholds separating normal, major, and paroxysmal events[8,14,15,16,17,18]. In-depth scrutiny of the eruptive activity before and during the two paroxysms was carried out using data from: (i) surveillance video-recordings, (ii) high-frequency thermal camera video-recordings, (iii) images from social media, (iv) field studies of eruption deposits, (v) vesicularity analysis in lapillisized and ash-sized products, and (vi) chemical composition of erupted products. The main scientific goal of this study is to use these integrated data to infer relatively longterm precursory signals of such hazardous events that apparently occurred unexpectedly
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