The evolution of hourly strombolian cycles towards paroxysmal activity at Etna volcano

Abstract Lava fountains are typical of basaltic volcanic eruptions, especially during paroxysms when activity shifts from intermittent Strombolian explosions to sustained high lava discharge often accompanied by ash emission. Cyclic eruptive behaviour –marked by regular variations in explosive intensity and lava fountaining over periods of minutes to hours– has been observed before but rarely captured in the geophysical record. In November 2023, Mt. Etna (Italy) exhibited cyclic Strombolian activity, which culminated in a paroxysm on 1 December, 2023. Over 10 days, clusters of frequent explosions recurred on an approximately hourly timescale from multiple vents within the volcano’s South East Crater (SEC). Infrasound data recorded by the INGV permanent network show repetitive waveforms, indicating consistent eruption dynamics and stable source characteristics. Seismic tremor locations point to a shallow source within the uppermost kilometer beneath the crater. The observations are consistent with episodic gas accumulation and release within the shallow plumbing system, potentially modulated by transient changes in near-vent conditions, and gas transfer through multiple dynamically connected pathways. These observations provide new insights into shallow eruptive processes at Mt. Etna, and, more generally, support models that link cyclic eruptive activity at basaltic volcanoes to near-surface gas accumulation and release.