Granular mixture deflation and generation of pore fluid pressure at the impact zone of a pyroclastic fountain: Experimental insights

Fries, Allan; Roche, Olivier; Carazzo, Guillaume

doi:10.1016/j.jvolgeores.2021.107226

Cited by 8 publications

(15 citation statements)

References 40 publications

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“…manuscript submitted to JGR: Solid Earth the PDC (Wilson, 1980;Roche et al, 2010;Valentine, 2020;Fries et al, 2021), which is then advected downstream by the flow, thus lowering the basal friction. Roche et al (2008) show experimentally that pore-fluid pressure leads to Newtonian fluid-like behavior of fluidized granular flows.…”

Section: Accepted Articlementioning

confidence: 99%

“…This fluidization is used to replicate the high mobility/low friction behavior and the interstitial gas pore pressure of dense PDCs observed experimentally and in the field (e.g. Wilson, 1980;Roche et al, 2010;Lube et al, 2019;Valentine, 2020;Fries et al, 2021), while also helping to overcome scaling issues (Rowley et al, 2014;G. M. Smith et al, 2018).…”

Section: Accepted Articlementioning

confidence: 99%

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Numerical simulations of a fluidized granular flow entry into water: insights into modeling tsunami generation by pyroclastic density currents

Battershill

Whittaker

Lane

et al. 2021

Preprint

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The tsunami generation potential of pyroclastic density currents (PDCs) entering the sea is poorly understood, due to limited data and observations. Thus far, tsunami generation by PDCs has been modeled in a similar manner to tsunami generation associated with landslides or debris flows, using two-layer depth-averaged approaches. Using the adaptive partial differential equation solver Basilisk and benchmarking with published laboratory experiments, this work explores some of the important parameters not yet accounted for in numerical models of PDC-generated tsunamis. We use assumptions derived from experimental literature to approximate the granular, basal flow component of a PDC as a dense Newtonian fluid flowing down an inclined plane. This modeling provides insight into how the boundary condition of the slope and the viscosity of the dense granular-fluid influence the characteristics of the waves generated. It is shown that the boundary condition of the slope has a first-order impact on the interaction dynamics between the fluidized granular flow and water, as well as the energy transfer from the flow to the generated wave. The experimental physics is captured well in the numerical model, which confirms the underlying assumption of Newtonian fluid-like behaviour in the context of wave generation. The results from this study suggest the importance of considering vertical density and velocity stratification in wave generation models. Furthermore, we demonstrate that granular-fluids more dense than water are capable of shearing the water surface and generating significant amplitude waves, despite vigorous overturning.

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Section: Accepted Articlementioning

confidence: 99%

Section: Accepted Articlementioning

confidence: 99%

Numerical simulations of a fluidized granular flow entry into water: insights into modeling tsunami generation by pyroclastic density currents

Battershill

Whittaker

Lane

et al. 2021

Preprint

View full text Add to dashboard Cite

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“…In particular, within the pyroclastic mixture, and especially at the impact zone of a collapsing fountain (Sweeney and Valentine 2017;Valentine and Sweeney 2018;Valentine 2020;Fries et al 2021), the differential motion between the interstitial gas (flowing relatively upwards) and the solid particles (moving relatively downward) is able to generate pore pressure, which counterbalances the weight of the particles, reduces friction and thus increases run-out distance (Iverson 1997;Savage and Iverson 2003;Goren et al 2010;Roche 2012;Rowley et al 2014;Breard et al 2019a). The temporal evolution of pore pressure, and thus its effective influence on run-out distance, depends on the balance between some source mechanisms (e.g.…”

Section: Introductionmentioning

confidence: 99%

The influence of gas pore pressure in dense granular flows: numerical simulations versus experiments and implications for pyroclastic density currents

et al. 2021

Self Cite

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We investigate the influence of gas pore pressure in granular flows through numerical simulations on horizontal and low-angle inclined surfaces. We present a two-phase formulation that allows description of dam-break experiments considering high-aspect-ratio collapsing columns and depth-dependent variations of flow properties. The model is confirmed by comparing its results with data of analogue experiments. The results suggest that a constant, effective pore pressure diffusion coefficient can be determined in order to reproduce reasonably well the dynamics of the studied dam-break experiments, with values of the diffusion coefficient consistent with experimental estimates from defluidizing static columns. The discrepancies between simulations performed using different effective pore pressure diffusion coefficients are mainly observed during the early acceleration stage, while the final deceleration rate, once pore pressure has been dissipated, is similar in all the studied numerical experiments.However, these short-lasting discrepancies in the acceleration stage can be manifested in large differences in the resulting run-out distance. We also analyze the pore pressure at different distances along the channel. Although our model is not able to simulate the under-pressure phase generated by the sliding head of the flows in experiments and measured beneath the flowsubstrate interface, the spatio-temporal characteristics of the subsequent over-pressure phase are compatible with experimental data. Additionally, we studied the deposition dynamics of the granular material, showing that the timescale of deposition is much smaller than that of the granular flow, while the time of the deposition onset varies as a function of the distance from the reservoir, being strongly controlled by the surface slope angle. The simulations reveal that an increment of the surface slope angle from 0° to 10° is able to increase significantly the flow run-out distance (by a factor between 2.05 and 2.25, depending on the fluidization conditions). This has major implications for pyroclastic density currents, which typically propagate at such gentle slope angles.

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“…Fluidized, micro‐meter ( d = 65 ± 10 μ m ) spherical glass beads are released from a lock and propagate down a ramp (with a continuous supply of air flow to maintain pore fluid pressure), before interacting with water. This fluidization is used to replicate the high mobility/low friction behavior and the interstitial gas pore pressure of dense PDCs observed experimentally and in the field (e.g., Fries et al., 2021; Lube et al., 2019; Roche et al., 2010; Valentine, 2020), while also helping to overcome scaling issues (Rowley et al., 2014; G. M. Smith et al., 2018). Notable features of the mixing zone include the generation of a vertical granular jet, a leading wave, and a turbulent mixing zone, similar to that observed by Freundt (2003).…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulations of a Fluidized Granular Flow Entry Into Water: Insights Into Modeling Tsunami Generation by Pyroclastic Density Currents

et al. 2021

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Introduction Volcanic TsunamisAround 80% of tsunamis are triggered by underwater earthquakes which cause a sudden and rapid displacement of the water surface. Due to the wavelengths associated with the large horizontal scale of the fault rupture (tens to hundreds of kms), this displacement results in long period waves capable of propagating across ocean basins (Center, 2006). Tsunamis can also be generated through sub-aerial and submarine landslides,

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Granular mixture deflation and generation of pore fluid pressure at the impact zone of a pyroclastic fountain: Experimental insights

Cited by 8 publications

References 40 publications

Numerical simulations of a fluidized granular flow entry into water: insights into modeling tsunami generation by pyroclastic density currents

Numerical simulations of a fluidized granular flow entry into water: insights into modeling tsunami generation by pyroclastic density currents

The influence of gas pore pressure in dense granular flows: numerical simulations versus experiments and implications for pyroclastic density currents

Numerical Simulations of a Fluidized Granular Flow Entry Into Water: Insights Into Modeling Tsunami Generation by Pyroclastic Density Currents

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