Assessment of risk associated with tephra-related hazards

Bonadonna, Costanza; Biasse, Sébastien; Menoni, Scira; Gregg, Chris E.

doi:10.1016/b978-0-12-818082-2.00008-1

Cited by 15 publications

(11 citation statements)

References 115 publications

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“…However, less attention has been paid to settling-driven gravitational instabilities that can develop at the base of volcanic clouds and result in the formation of downward moving plumes, called ash fingers, within which fine ash particles fall faster than they do individually. Tephra dispersal and sedimentation can affect communities at multiple spatial and temporal scales (Jenkins et al, 2015;Bonadonna et al, 2021) including disruption to aviation (Guffanti et al, 2009;Prata and Tupper, 2009;Lechner et al, 2017), impact to public health (Horwell and Baxter, 2006;Gudmundsson, 2011) and damage to both residential buildings and critical infrastructures (Spence et al, 2005;Wilson et al, 2012). Therefore, understanding the processes controlling tephra sedimentation, including settling-driven gravitational instabilities, is fundamental for developing more efficient ash dispersal models and better managing the associated risk (Scollo et al, 2008;Folch, 2012;Durant, 2015).…”

Section: Introductionmentioning

confidence: 99%

The Influence of Particle Concentration on the Formation of Settling-Driven Gravitational Instabilities at the Base of Volcanic Clouds

Fries

Lemus

Jarvis³

et al. 2021

Front. Earth Sci.

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Settling-driven gravitational instabilities observed at the base of volcanic ash clouds have the potential to play a substantial role in volcanic ash sedimentation. They originate from a narrow, gravitationally unstable region called a Particle Boundary Layer (PBL) that forms at the lower cloud-atmosphere interface and generates downward-moving ash fingers that enhance the ash sedimentation rate. We use scaled laboratory experiments in combination with particle imaging and Planar Laser Induced Fluorescence (PLIF) techniques to investigate the effect of particle concentration on PBL and finger formation. Results show that, as particles settle across an initial density interface and are incorporated within the dense underlying fluid, the PBL grows below the interface as a narrow region of small excess density. This detaches upon reaching a critical thickness, that scales with (ν2/g′)1/3, where ν is the kinematic viscosity and g′ is the reduced gravity of the PBL, leading to the formation of fingers. During this process, the fluid above and below the interface remains poorly mixed, with only small quantities of the upper fluid phase being injected through fingers. In addition, our measurements confirm previous findings over a wider set of initial conditions that show that both the number of fingers and their velocity increase with particle concentration. We also quantify how the vertical particle mass flux below the particle suspension evolves with time and with the particle concentration. Finally, we identify a dimensionless number that depends on the measurable cloud mass-loading and thickness, which can be used to assess the potential for settling-driven gravitational instabilities to form. Our results suggest that fingers from volcanic clouds characterised by high ash concentrations not only are more likely to develop, but they are also expected to form more quickly and propagate at higher velocities than fingers associated with ash-poor clouds.

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Section: Introductionmentioning

confidence: 99%

The Influence of Particle Concentration on the Formation of Settling-Driven Gravitational Instabilities at the Base of Volcanic Clouds

Fries

Lemus

Jarvis³

et al. 2021

Front. Earth Sci.

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“…Explosive volcanic eruptions can inject large quantities of ash into the atmosphere, generating multiple hazards at various spatial and temporal scales (Blong, 2000;Bonadonna et al, 2021). Subsequent volcanic ash dispersal and sedimentation can strongly disrupt air traffic (Guffanti et al, 2008;Prata and Rose, 2015), affect inhabited areas (Spence et al, 2005;Jenkins et al, 2015), and impact ecosystems and public health (Gudmundsson, 2011;Wilson et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Modelling Settling-Driven Gravitational Instabilities at the Base of Volcanic Clouds Using the Lattice Boltzmann Method

et al. 2021

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Field observations and laboratory experiments have shown that ash sedimentation can be significantly affected by collective settling mechanisms that promote premature ash deposition, with important implications for dispersal and associated impacts. Among these mechanisms, settling-driven gravitational instabilities result from the formation of a gravitationally-unstable particle boundary layer (PBL) that grows between volcanic ash clouds and the underlying atmosphere. The PBL destabilises once it reaches a critical thickness characterised by a dimensionless Grashof number, triggering the formation of rapid, downward-moving ash fingers that remain poorly characterised. We simulate this process by coupling a Lattice Boltzmann model, which solves the Navier-Stokes equations for the fluid phase, with a Weighted Essentially Non Oscillatory (WENO) finite difference scheme which solves the advection-diffusion-settling equation describing particle transport. Since the physical problem is advection dominated, the use of the WENO scheme reduces numerical diffusivity and ensures accurate tracking of the temporal evolution of the interface between the layers. We have validated the new model by showing that the simulated early-time growth rate of the instability is in very good agreement with that predicted by linear stability analysis, whilst the modelled late-stage behaviour also successfully reproduces quantitative results from published laboratory experiments. The results show that the model is capable of reproducing both the growth of the unstable PBL and the non-linear dependence of the fingers’ vertical velocity on both the initial particle concentration and the particle diameter. Our validated model is used to expand the parameter space explored experimentally and provides key insights into field studies. Our simulations reveal that the critical Grashof number for the instability is about ten times larger than expected by analogy with thermal convection. Moreover, as in the experiments, we found that instabilities do not develop above a given particle threshold. Finally, we quantify the evolution of the mass of particles deposited at the base of the numerical domain and demonstrate that the accumulation rate increases with time, while it is expected to be constant if particles settle individually. This suggests that real-time measurements of sedimentation rate from volcanic clouds may be able to distinguish finger sedimentation from individual particle settling.

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“…Considering the cascading and complex nature of ashfall hazards (Blake et al., 2017; Bonadonna et al., 2021; Deligne et al., 2017; Wilson et al., 2012) as implied by the central authorities as well, evacuation zones can also be expanded by considering the secondary disasters that can occur after an eruption, such as debris flows, and loss of services such as transportation and electricity. Historical records also stated that about a month after the Taisho eruption, several debris flows occurred in the southwestern parts of Sakurajima volcano, flooding and destroying a considerable number of villages (Kagoshima City, 2021).…”

Section: Methods and Datamentioning

confidence: 99%

“…So far, the PUFF model has shown good accuracy for smaller eruptions of Sakurajima volcano (Iguchi et al, 2020(Iguchi et al, , 2022Tanaka & Iguchi, 2019;Tanaka et al, 2020). However, since large eruptions have been rare in recent centuries (Bonadonna et al, 2021;Iguchi, 2020), the model's performance in simulating large eruptions of Sakurajima volcano is still unconfirmed. Therefore, it is of utmost importance for decision makers to understand the uncertainties in the current system when predicting ash distribution over large areas in order to disseminate warnings to citizens and when to start the evacuation process.…”

Section: Introductionmentioning

confidence: 99%

Uncertainty Analysis of the Prediction of Massive Ash Fallout From a Large Explosive Eruption at Sakurajima Volcano

Rahadianto,

Tatano,

Iguchi

2024

Earth and Space Science

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Volcanic ash hazards present life‐threatening dangers to populations near volcanoes during large explosive eruptions. Vulnerable infrastructures demand a comprehensive disaster risk reduction strategy to protect residents from enormous ashfall accumulations. To prepare for the next large eruption of Sakurajima volcano, authorities in Kagoshima City are developing a countermeasure plan utilizing ash dispersal prediction 24 hr before an eruption. However, the absence of large eruptions in the last century makes it challenging to confirm the accuracy of predictions for hazard area designation. To ensure established protocols are effective, uncertainties in ashfall predictions must be addressed, enabling authorities to make appropriate responses. We simulated the previous large eruption of Sakurajima volcano using multiple wind forecast lead times as historical predictions from July 2018 to December 2022. The uncertainty in prediction results was evaluated by comparing simulation outputs with validation data from the ash dispersal data set. We examined uncertainty in hazard area assignment and its variation depending on risk items, wind field states, and the influences of seasonal patterns and events. Updating ashfall predictions with improved wind forecasts reduces uncertainty for all risk items and increases the precision of identified hazard zones. Furthermore, uncertainty levels are influenced by seasonality and can shift significantly with varying wind strengths controlling ash dispersal process. Providing uncertainty information is vital for decision‐making during ash fallout events, and it is recommended to update response decisions 12 hr after the initial prediction. This study's outcomes will aid in developing better disaster risk management strategies, focusing on volcanic ash hazards.

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Assessment of risk associated with tephra-related hazards

Cited by 15 publications

References 115 publications

The Influence of Particle Concentration on the Formation of Settling-Driven Gravitational Instabilities at the Base of Volcanic Clouds

The Influence of Particle Concentration on the Formation of Settling-Driven Gravitational Instabilities at the Base of Volcanic Clouds

Modelling Settling-Driven Gravitational Instabilities at the Base of Volcanic Clouds Using the Lattice Boltzmann Method

Uncertainty Analysis of the Prediction of Massive Ash Fallout From a Large Explosive Eruption at Sakurajima Volcano

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