High-speed imaging, acoustic features, and aeroacoustic computations of jet noise from Strombolian (and Vulcanian) explosions

Abstract

High-speed imaging of explosive eruptions at Stromboli (Italy), Fuego (Guatemala), and Yasur (Vanuatu) volcanoes allowed visualization of pressure waves from seconds-long explosions. From the explosion jets, waves radiate with variable geometry, timing, and apparent direction and velocity. Both the explosion jets and their wave fields are replicated well by numerical simulations of supersonic jets impulsively released from a pressurized vessel. The scaled acoustic signal from one explosion at Stromboli displays a frequency pattern with an excellent match to those from the simulated jets. We conclude that both the observed waves and the audible sound from the explosions are jet noise, i.e., the typical acoustic field radiating from high-velocity jets. Volcanic jet noise was previously quantified only in the infrasonic emissions from large, sub-Plinian to Plinian eruptions. Our combined approach allows us to define the spatial and temporal evolution of audible jet noise from supersonic jets in small-scale volcanic eruptions.

Volcanic eruption volume flux estimations from very long period infrasound signals

“…Sparks et al [1997] compiled data of eruptions accompanying a strong plume, which have much longer duration and higher column heights than the eruptions examined in the present study. Although we recognize such a considerable difference in the eruptions highlighted in both studies, we examine the relationship between the infrasound-derived flux and the empirical relation given by Sparks et al [1997], to discuss the capability of the column height and magma flux estimation using the IVLP signals. Figure 5c shows the relationship between the average infrasound-derived flux (equivalent to V/T) and the column height H of each eruption [Japan Meteorological Agency, 2014, 2015a, 2015b, 2016a, 2016bShimbori et al, 2013].…”

“…Although several studies attempted to estimate the column height with infrasound data [e.g., Caplan-Auerbach et al, 2010], it has proven challenging. Sparks et al [1997] proposed an empirical equation for the column height H (km) and magma volume flux Q vol (m 3 /s): H = 1.67Q vol 0.259 .…”

“…Volcanic infrasound observed near active vents (<10 km) is valuable in understanding eruption dynamics [e.g., Johnson and Ripepe, 2011]. Infrasound at periods shorter than 10 s can be explained by an explosion, the bursting of bubbles [e.g., Vergniolle and Brandeis, 1994], resonance at the vent cavity [Fee et al, 2010;Lyons et al, 2016], and the turbulent jets that accompany the eruption column [Matoza et al, 2009;Taddeucci et al, 2014]. In particular, infrasound excited by a discrete explosion is well explained by assuming a monopole source at the vent [Kim et al, 2015].…”

Application of the Monopole Source to Quantify Explosive Flux during Vulcanian Explosions at Sakurajima Volcano (Japan)

“…Although the monopole source is postulated as a suitable approximation for purely explosive transients, higher order dipole and quadrupole acoustic sources (Woulff and McGetchin, 1976;Johnson et al, 2008;Kim et al, 2012) and jet noise (Matoza et al, 2009;Taddeucci et al, 2014) have been proposed for a range of volcanic eruptive activities. Both jet noise and dipole type sources radiate sound less efficiently than a monopole source (for given eruption energetics) and are thought to radiate sound with an axisymmetric symmetry (Dowling, 1998).…”

“…Both jet noise and dipole type sources radiate sound less efficiently than a monopole source (for given eruption energetics) and are thought to radiate sound with an axisymmetric symmetry (Dowling, 1998). Jet noise is also associated with noncompact source regions extending from the vent and up through a collimated jet (Taddeucci et al, 2014). Although Johnson et al (2008) found the dipole acoustic component to be minor compared to the monopole component for strombolian explosions at Erebus, other eruptions, such as those of Sakurajima, may reflect more complex volumetric and nonvolumetric contributions (Matoza et al, 2014;this Focus Section).…”