Supplementary Material to "geophysical Fingerprint of the 4–11 July 2024 Eruptive Activity at Stromboli Volcano, Italy"

Abstract. Paroxysmal eruptions, characterized by sudden and vigorous explosive activity, are common events at many open-vent volcanoes. Stromboli volcano, Italy, is well-known for its nearly continuous degassing activity and mild explosions from the summit craters, occasionally punctuated by energetic, short-lived paroxysms. Here, we analyse multi-parameter geophysical data recorded at Stromboli in early July 2024, during activity that led to a paroxysmal eruption on 11 July. We use seismic, infrasound and ground deformation data, complemented by visual and Unoccupied Aircraft System observations, to identify key geophysical precursors to the explosive activity and reconstruct the sequence of events. Elevated levels of volcanic tremor and Very Long Period (VLP) seismicity accompanied moderate explosive activity, lava emission and small collapses from the north crater, leading to a major explosion on 4 July, 2024 at 12:16 (UTC). Collapse activity from the North crater area continued throughout July 7, while effusive activity occurred from two closely-spaced vents located on the Sciara del Fuoco slope, on the Northwest flank of the volcano. On 11 July, a rapid increase in ground deformation preceded, by approximately 10 minutes, a paroxysmal event at 12:08 (UTC); the explosion produced a 5 km-high eruptive column and pyroclastic density currents along Sciara del Fuoco. We infer that the early activity in July was linked to eruption of resident magma within the shallowest parts of the volcano plumbing. This was followed by lowering of the magma level within the conduit system as indicated by the location of newly opened effusive vents The rapid inflation observed before the paroxysmal explosion on 11 July is consistent with the rapid expansion of gas-rich magma rising from depth, as frequently suggested at Stromboli during energetic explosive events. Our results provide additional valuable insights into the eruptive dynamics of Stromboli and other open-conduit volcanoes, and emphasize the importance of integrated geophysical observations for understanding eruption dynamics, their forecasting and associated risk mitigation.