Infrasonic gliding reflects a rising magma column at Mount Etna (Italy)

Abstract

Infrasound is increasing applied as a tool to investigate magma dynamics at active volcanoes, especially at open-vent volcanoes, such as Mt. Etna (Italy), which are prodigious sources of infrasound. Harmonic infrasound signals have been used to constrain crater dimensions and track the movement of magma within the shallow plumbing system. This study interprets the remarkable systematic change in monotonic infrasound signals preceding a lava fountaining episode at Mt. Etna on 20 February 2021. We model the changing tones (0.7 to 3 Hz fundamental frequency) as a rise in the magma column from 172 ± 25 m below the crater rim to 78 ± 8 m over the course of 24 h. The infrasonic gliding disappears approximately 4 h before the onset of lava fountaining as the magma column approaches the flare of the crater and acoustic resonance is no longer supported. The featured 20 February event was just one of 52 lava fountain episodes that occurred at Mt. Etna over the course of 9 months in 2021 and was the only lava fountain episode where dramatic gliding was observed as a subsequent partial collapse of the crater prevented future resonance. The results presented here demonstrate that analysis of infrasonic gliding can be used to track the position of the magma free surface and hence may provide information on the processes taking place within the plumbing system before eruptive activity.

Assessment of eruption source parameters using infrasound: a case study from the 2021 eruption of Mt.Etna, Italy

“…3c). Finally, we used a vent radius of 10m 44 to convert VER into ow velocity and calculated its 1-minute median, which is shown in Fig. 3c (yellow circles).…”

Volcano Opto‐Acoustics: Mapping the Infrasound Wavefield at Yasur Volcano (Vanuatu)

“…Our optically‐derived speeds within the inner crater (ic) are 750–1,500 m/s (Figure 5b), which are far faster than reasonable supersonic sound speeds and/or for high intrinsic sound speeds (due to the presence of hot crater gases). Crater gas temperature is not expected to exceed a few hundred °C (e.g., Sawyer et al., 2008; Fee et al., 2010) giving rise to sound speeds no faster than ∼450 m/s (e.g., Sciotto et al., 2022). The probable explanation for the perceived high velocities ranging from 750 to 1,500 m/s is that they are due to perspective view.…”

“…While it is possible that resonant infrasound originates in natural voids, such as those left after bubble slug bursts (e.g., Kremers et al., 2013; Vergniolle & Brandeis, 1996) or in Helmholtz cavities (e.g., Fee et al., 2010; Goto & Johnson, 2011; Sciotto et al., 2013), resonance is also numerically modeled when crater depth is large compared to diameter (Johnson, Ruiz, et al., 2018; Lyons et al., 2016; Spina et al., 2014; Watson et al., 2019). Several studies have reported on crater acoustic response changing with time and attributed this to dynamic crater morphology as magma levels change (e.g., Johnson, Watson, et al., 2018; Richardson et al., 2014; Sciotto et al., 2022; Watson et al., 2020).…”

“…Yasur's sporadic explosion infrasound, occurring every few minutes, is a persistent feature and is also accompanied by sustained infrasound tremor (e.g., Spina et al., 2015), excited by vents in both craters. Continuous infrasonic tremor may be intense (>1 Pa at 1 km) and is a common feature at many open‐vent volcanoes with lava lakes and/or exposed magma columns (e.g., Stromboli (Ripepe et al., 1996), Kilauea (Fee et al., 2010), Villarrica (Rosenblatt et al., 2022), and Etna (Sciotto et al., 2022)). It can be present between explosions and/or when explosions are absent, and may be excited by roiling of the magma surface and/or by vigorous degassing (e.g., Ripepe et al., 2010; Goto & Johnson, 2011).…”

“…• Time series pixel brightness data from cameras show a strong correlation with co-located infrasound records • Video image processing can be used to extract the spatial infrasound wavefield produced at open-vent volcanoes • Radiation of sound waves, existence of standing waves, and crater acoustic response may be investigated with volcano opto-acoustics Watson et al, 2019). Several studies have reported on crater acoustic response changing with time and attributed this to dynamic crater morphology as magma levels change (e.g., Johnson, Watson, et al, 2018;Richardson et al, 2014;Sciotto et al, 2022;Watson et al, 2020).…”