Inferring pyroclastic density current flow conditions using syn-depositional sedimentary structures

Pollock, Nicholas; Brand, Brittany D.; Rowley, Pete; Sarocchi, Damiano; Sulpizio, Roberto

doi:10.1007/s00445-019-1303-z

Cited by 20 publications

(33 citation statements)

References 65 publications

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“…In addition, the mixing structures produced in our experiments resemble recumbent flame structures found in the deposits of turbidity currents (Dasgupta, 1998), pyroclastic currents (Rowley et al, 2011;Douillet et al, 2018;Pollock et al, 2019), and tsunamis (Matsumoto et al, 2008). Following previous studies, we suggest that the structures form as the result of granular shear instabilities formed at the flow-bed interface (Rowley et al, 2011;Farin et al, 2014;Pollock et al, 2019).…”

Section: Mechanism Of Erosionsupporting

confidence: 83%

“…Following previous studies, we suggest that the structures form as the result of granular shear instabilities formed at the flow-bed interface (Rowley et al, 2011;Farin et al, 2014;Pollock et al, 2019). The morphology of these mixing structures may reflect conditions within the flow (Rowley et al, 2011;Pollock et al, 2019), and similar experiments to those presented here may provide the ability to extract scaling relationships that relate the dimensions of the structures to flow parameters. However, a full analysis of the evolution of these structures and the potential derivation of scaling relationships is outside the scope of this study.…”

Section: Mechanism Of Erosionsupporting

confidence: 78%

“…. .11 Structure length versus structure height plotted for our experimental data (gray diamonds) and field data from recumbent flame structures measured in the deposits of pyroclastic currents produced during the May 18, 1980 eruption of Mount St Helens (gray circles; data from Pollock et al 2019). Strong correlation for the height versus length for both the experimental and field data suggesting the structures are all formed by the same process of granular shear instabilities generating mixing at the flow-bed interface.…”

Section: List Of Tablesmentioning

confidence: 86%

“…Sparks 1976;Calder et al 2000;Druitt et al 2002;Brand et al 2014b), and in some cases can provide quantitative information about the flow conditions at the time of deposition (e.g. Clarke and Voight 2000;Dellino and La Volpe 2000;Taddeucci and Palladino 2002;Brand et al 2014;Pollock et al 2019). Analogue experiments and numerical models provide the ability to quantitatively investigate the behavior of simulated currents in controlled environments (e.g.…”

Section: List Of Tablesmentioning

confidence: 99%

“…These experimental studies propose that the erosion and mixing occurs because of the formation of granular shear instabilities at the flow-bed interface (Rowley et al 2011;Farin et al 2014). Additionally, field studies on the deposits of pyroclastic currents reveal sedimentary structures that suggest syn-depositional mixing between the flow and its bed (Rowley 2010;Douillet et al 2018;Pollock et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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Synthesizing Field and Experimental Techniques to Investigate the Enigmatic Processes Occurring at the Base of Pyroclastic Currents

Pollock¹

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the structures suggests deposition rates of 4 to 32 cm s-1. Such high deposition rates indicate that the deposits likely accumulated in a stepwise manner, rather than either progressively or en masse. The structures suggest that sections of the deposit accumulated during punctuated periods of high deposition lasting at most a few seconds followed by periods of bypassing (i.e. non-deposition) or erosion lasting minutes to tens of minutes. Our findings motivate continued experimental and numerical work to understand how the formation of recumbent flame (and similar) structures affects subsequent flow behavior in terms of runout distance and hazard potential.

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Section: Mechanism Of Erosionsupporting

confidence: 83%

Section: Mechanism Of Erosionsupporting

confidence: 78%

Section: List Of Tablesmentioning

confidence: 86%

Section: List Of Tablesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synthesizing Field and Experimental Techniques to Investigate the Enigmatic Processes Occurring at the Base of Pyroclastic Currents

Pollock¹

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Subaerial Pyroclastic Density Currents (Pyroclastic Flows and Surges)

Giordano,

Cas,

Wright

2024

Springer Textbooks in Earth Sciences, Geography and Environment

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The mysterious grooves of Volcán Bárcena: a review of the role of streamwise counter-rotating vortices during erosion by dilute pyroclastic density currents

et al. 2021

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Although erosion during high-energy passage of a pyroclastic density current (PDC) causes great damage, analyses of the effects of such erosion are sparse in scientific literature compared to observations and interpretations of depositional processes. In this paper, we review observations of surfaces where PDCs have eroded sets of grooves that provide information on the erosion process. We postulate that in some cases, the grooves were carved by streamwise vortices in the boundary layer of the PDC and review possible fluid dynamic instabilities that can give rise to such vortices. For the prominent grooves at Volcán Bárcena, Mexico, we propose that a fluid dynamic instability, which we dub the "groovy instability," occurred and caused formation of erosive counter-rotating vortices. This instability occurs when the particle concentration boundary layer thickness, δ c , is larger than the velocity (shear) boundary layer thickness, δ u , i.e., L=δ c /δ u >1. In subaqueous turbidity currents, these vortices have a typical wavelength of~25*δ c . If this relation is applied to the grooves formed on Volcán Bárcena, the inferred particle concentration boundary layer is estimated to have been <1 m thick. We postulate that a transition between erosion of grooves and deposition of dunes at Volcán Bárcena occurred when hydraulically supercritical flow on the upper flanks changed to subcritical flow about halfway down the mountain. We call attention to boundary layer dynamics in erosive pyroclastic density currents at a dimension that is difficult to scale quantitatively in laboratory experiments and is usually not resolved computationally and to the need for incorporating such dynamics into models of PDC dynamics.

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Inferring pyroclastic density current flow conditions using syn-depositional sedimentary structures

Cited by 20 publications

References 65 publications

Synthesizing Field and Experimental Techniques to Investigate the Enigmatic Processes Occurring at the Base of Pyroclastic Currents

Synthesizing Field and Experimental Techniques to Investigate the Enigmatic Processes Occurring at the Base of Pyroclastic Currents

Subaerial Pyroclastic Density Currents (Pyroclastic Flows and Surges)

The mysterious grooves of Volcán Bárcena: a review of the role of streamwise counter-rotating vortices during erosion by dilute pyroclastic density currents

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