Monochromatic infrasound waves observed during the 2014–2015 eruption of Aso volcano, Japan

Yokoo, Akihiko; Ishii, Kosuke; Ohkura, Takahiro; Kim, Kee Hoon

doi:10.1186/s40623-019-0993-y

Cited by 20 publications

(16 citation statements)

References 35 publications

(41 reference statements)

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“…The methodology here proposed is, for the first time, taking in consideration the acoustic propagation in the conduit by considering the effect of the conduit on the acoustic propagation outside the vent. We suggest that when linear theory of sound is applied to acoustic waves generated in the conduit (Diaz‐Moreno et al, 2019; Fee, Izbekov et al, 2017; Iezzi et al, 2019; Johnson et al, 2018; Kim et al, 2015; Watson et al, 2019; Yokoo et al, 2019), the effect of the impedance contrast between the open‐end vent and the atmosphere cannot be neglected to properly assess the source parameters and/or propagation outside the explosive vent.…”

Section: Resultsmentioning

confidence: 98%

Modeling the Acoustic Flux Inside the Magmatic Conduit by 3D‐FDTD Simulation

Lacanna

Ripepe

2020

JGR Solid Earth

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Infrasound measurements at open-vent volcanoes are crucial parameters for monitoring and exploring the explosive source dynamics. Volcano infrasound depicts the pressure variation within the volcanic conduit generated by the sudden expansion of volcanic gases during the fragmentation process, and it can provide important constraints on the explosive source parameters (i.e., volumetric flux and exit velocity). The acoustic source of volcanic explosions is modeled by infrasonic signals measured near the volcano vent (<3 km) assuming linear theory of sound and considering the effects of topography and atmosphere on the acoustic wavefield. However, little is known on the initial conditions within the volcanic conduit. In linear acoustics, the wavefield in a cylindrical duct propagates as a plane wavefront, which becomes spherical outside the vent. The acoustic impedance at the open end of the duct is a function of the vent radius and the pressure wavelength, and it controls the acoustic wavefield radiated outside the duct in terms of amplitude and radiation pattern. We present here a 3D-Finite Difference Time Domain (FDTD) numerical method to evaluate the scattering effects on the infrasound signal produced by topography around the crater and along the source-receiver path in terms of Green's function. Once the effects of topography are removed, we show how pressure perturbation is largely affected by the impedance contrast at the vent which, when not considered, is introducing errors in the way we quantify explosive dynamics.

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Section: Resultsmentioning

confidence: 98%

Modeling the Acoustic Flux Inside the Magmatic Conduit by 3D‐FDTD Simulation

Lacanna

Ripepe

2020

JGR Solid Earth

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“…Signals in the same frequency band were also observed continuously during the entire period of the 2014-2015 eruption, regardless of the surficial phenomenon at the vent, such as ash venting, Strombolian explosion, steam or gas emission, or no activity (Yokoo et al 2019). This signal might be related to the resonant tone of the space in the conduit above the magma surface and may be triggered by an incident signal such as an explosion (Yokoo et al 2019). The 2 Hz wave appeared to emerge at almost the same time as the 0.5 Hz amplification.…”

Section: Observation and Datamentioning

confidence: 84%

Gas flow dynamics in the conduit of Strombolian explosions inferred from seismo-acoustic observations at Aso volcano, Japan

Ishii

Yokoo

Kagiyama

et al. 2019

Earth Planets Space

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Strombolian explosions are one of the most studied eruptive styles and are characterized by intermittent explosions. The mechanism of a Strombolian explosion is modeled as a large gas pocket (slug) migrating through the magma conduit and then bursting at the air-magma interface. These ascending and bursting processes of the slug induce characteristic seismo-acoustic signals during each explosion: very-long-period (VLP) seismic signals, eruption earthquake signals, and infrasound signals. However, at Stromboli volcano, it has been reported that the ascent velocity estimated from the time differences between observed signals is nearly an order of magnitude higher than that expected from laboratory experiments simulating slug ascent. This discrepancy between observation-based and experiment-based velocities has not yet been fully explained and strongly suggests that the conventional model of Strombolian explosions should be partially revised. In this study, we attempted to validate the model of Strombolian explosions by estimating the gas phase velocity in the conduit in the case of Aso volcano. We recorded seismo-acoustic signals accompanying Strombolian events at Aso volcano, Japan, in late April 2015 via our monitoring network, and the ascent velocity of the gas phase was determined from the difference in arrival times between the VLP signals and the infrasound signals. Our estimated velocity exceeded 100 m/s, which is much faster than the experimental value of 7.5 m/s predicted for Aso volcano. To explain this rapid ascent velocity, we propose a revised model describing the migration of the gas phase via a more complicated mechanism, such as annular flow. In this model, we assumed that the gas phase ascends in the conduit at high velocity while making a pathway leading to the magma surface, most likely due to a temporary increase in the gas flux. Our model will help to deepen the understanding of the complicated dynamics in the magma conduit during a Strombolian explosion.

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“…The relationship between pixel value and the actual length was calculated using a digital elevation model (DEM) and the obtained images. The DEM was constructed using the UAV observation of Yokoo et al (2019). Consequently, the horizontal resolution was 5.81 cm/pixel and the vertical resolution was 3.95 cm/pixel.…”

Section: Image Analysismentioning

confidence: 99%

Transport of ballistic projectiles during the 2015 Aso Strombolian eruptions

Tsunematsu

Ishii

Yokoo

2019

Earth Planets Space

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Large pyroclasts-often called ballistic projectiles-cause many casualties and serious damage on people and infrastructures. One useful measure of avoiding such disasters is to numerically simulate the ballistic trajectories and forecast where large pyroclasts deposit. Numerical models are based on the transport dynamics of these particles. Therefore, in order to accurately forecast the spatial distribution of these particles, large pyroclasts from the 2015 Aso Strombolian eruptions were observed with a video camera. In order to extrapolate the mechanism of particle transport, we have analyzed the frame-by-frame images and obtained particle trajectories. Using the trajectory data, we investigated the features of Strombolian activity such as ejection velocity, explosion energy, and particle release depth. As gas flow around airborne particles can be one of the strongest controlling factors of particle transport, the gas flow velocities were estimated by comparing the simulated and observed trajectories. The range of the ejection velocity of the observed eruptions was 5.1-35.5 m/s, while the gas flow velocity, which is larger than the ejection velocity, reached a maximum of 90 m/s, with mean values of 25-52 m/s for each bursting event. The particle release depth, where pyroclasts start to move separately from the chunk of magmatic fragments, was estimated to be 11-13 m using linear extrapolation of the trajectories. Although these parabolic trajectories provide us with an illusion of particles unaffected by the gas flow, the parameter values show that the particles are transported by the gas flow, which is possibly released from inside the conduit.

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Monochromatic infrasound waves observed during the 2014–2015 eruption of Aso volcano, Japan

Cited by 20 publications

References 35 publications

Modeling the Acoustic Flux Inside the Magmatic Conduit by 3D‐FDTD Simulation

Modeling the Acoustic Flux Inside the Magmatic Conduit by 3D‐FDTD Simulation

Gas flow dynamics in the conduit of Strombolian explosions inferred from seismo-acoustic observations at Aso volcano, Japan

Transport of ballistic projectiles during the 2015 Aso Strombolian eruptions

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