Multi-parametric study of an eruptive phase comprising unrest, major explosions, crater failure, pyroclastic density currents and lava flows: Stromboli volcano, 1 December 2020–30 June 2021

Abstract

Open conduit volcanoes like Stromboli can display elusive changes in activity before major eruptive events. Starting on December 2020, Stromboli volcano displayed an increasing eruptive activity, that on 19 May 2021 led to a crater-rim collapse, with pyroclastic density currents (PDCs) that spread along the barren NW flank, entered the sea and ran across it for more than 1 km. This episode was followed by lava flow output from the crater rim lasting a few hours, followed by another phase of lava flow in June 2021. These episodes are potentially very dangerous on island volcanoes since a landslide of hot material that turns into a pyroclastic density current and spreads on the sea surface can threaten mariners and coastal communities, as happened at Stromboli on 3 July and 28 August 2019. In addition, on entering the sea, if their volume is large enough, landslides may trigger tsunamis, as occurred at Stromboli on 30 December 2002. In this paper, we present an integration of multidisciplinary monitoring data, including thermal and visible camera images, ground deformation data gathered from GNSS, tilt, strainmeter and GBInSAR, seismicity, SO2 plume and CO2 ground fluxes and thermal data from the ground and satellite imagery, together with petrological analyses of the erupted products compared with samples from previous similar events. We aim at characterizing the preparatory phase of the volcano that began on December 2020 and led to the May–June 2021 eruptive activity, distinguishing this small intrusion of magma from the much greater 2019 eruptive phase, which was fed by gas-rich magma responsible for the paroxysmal explosive and effusive phases of July–August 2019. These complex eruption scenarios have important implications for hazard assessment and the lessons learned at Stromboli volcano may prove useful for other open conduit active basaltic volcanoes.

Volcano generated tsunami recorded in the near source

“…Using the same granular landslide empirical equations (see Methods) and considering a slide width b ranging between 150 and 200 m, the amplitude of the tsunami is consistent with a volume of 0.71 ± 0.15 × 10 5 m 3 for a slide thickness = 6.5 ± 1 m. This volume is well in harmony with the 0.8 × 10 5 m 3 volume of material collapsed from the north flank of the NE crater estimated from images taken by helicopter immediately after the failure 47 .…”

“…4b ), the tsunami was height, almost the same of the 28 August 2019 tsunami, and it moved with a similar celerity c = 36.7 m/s. The dense ash cloud rising up from lapilli and scoriae ejected by the explosions made not possible to track the front velocity of the pyroclastic density current using our visible camera, we then assumed the mean front velocity previously estimated by thermal camera 47 …”

Cascading Machine Learning to Monitor Volcanic Thermal Activity Using Orbital Infrared Data: From Detection to Quantitative Evaluation

“…Stromboli is characterized by persistent explosive activity (Figure 8a) that can sometimes turn into more intense events, producing major explosions or paroxysmal events [36,37]. These can erupt as lava flows, such as in summer 2019, when two paroxysm events occurred [16]; in this case, the cascading algorithm detected a hot area of 273,600 m 2 on 22 July 2019.…”

Seismic and thermal precursors of crater collapses and overflows at Stromboli volcano

“…Fortunately, this tsunami didn’t cause any casualties, but some people were injured. In recent decades Stromboli showed an increase in eruptive activity and produced dangerous phenomena such as lava flows, paroxysms 8 , pyroclastic flows, major explosions, and crater collapses 1 , 9 – 12 . The main effusive phases occurred in the years 2002-2003 13 – 15 , 2007 16 , 2014 10 , and 2019 8 .…”

“…The main effusive phases occurred in the years 2002-2003 13 – 15 , 2007 16 , 2014 10 , and 2019 8 . In addition to these effusive phases, minor lava overflows (hereinafter referred to as overflows) often occurred (at least 78 from September 2008 4 , 12 , 17 , 18 ) which have affected the morphology of the Sciara del Fuoco 1 , 11 , 12 , 18 . Although the overflows are generally short-lived events, they can destabilize the slope of the Sciara del Fuoco, especially when they reach the sea rapidly.…”