Syn-eruptive, soft-sediment deformation of deposits from dilute pyroclastic density current: triggers from granular shear, dynamic pore pressure, ballistic impacts and shock waves

Douillet, Guilhem Amin; Taisne, Benoît; Tsang-Hin-Sun, Eve; Müller, Sebastian K.; Kueppers, Ulrich; Dingwell, Donald B.

doi:10.5194/se-6-553-2015

Cited by 26 publications

(15 citation statements)

References 88 publications

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“…We suggest that the soft sediment deformation at Ubehebe actually occurred under dry conditions, as indicated by all other characteristics of the deposits. Pore-gas pressure in the lowpermeability, fine-grained deposits facilitated deformation (see also Douillet et al, 2015). Emplacement of bedding subsets by individual explosions in rapid succession produced conditions where impacts of large clasts and clusters of clasts easily deformed fresh deposits that were still soft (fluid-like) due to pore pressure.…”

Section: Discussionmentioning

confidence: 96%

“…Crowe and Fisher (1973) briefly described contorted bedding and possible origins due to overriding surges, seismicity, and creep. Douillet et al (2015) cataloged examples from Ubehebe in their survey of soft sediment deformation in several pyroclastic surge deposits around the world, finding several types of structures, including flames, folds, thrust faults, curls, pull-aparts, potatoids, and impact sags. They attributed some structures to impact and some to density contrasts between rapidly emplaced beds causing Rayleigh-Taylor instabilities, with denser layers sinking into less-dense layers and vice versa, sometimes accompanied by shear of overriding pyroclastic surges to produce bent flames and vortex structures.…”

Section: Discussionmentioning

confidence: 99%

“…Folded structures (e.g., Figs. 3C and 3D) were interpreted to have formed during slumping of "wet sediment" (Douillet et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

“…Soft sediment deformation structures are common in fine-grained pyroclastic deposits. Deposits of dilute pyroclastic currents (pyroclastic surges) are among the most common hosts of such deformation (Douillet et al, 2015). Structures that indicate plastic deformation of a deposit are often taken as evidence that it was damp and cohesive.…”

Section: Introductionmentioning

confidence: 99%

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Soft sediment deformation in dry pyroclastic deposits at Ubehebe Crater, Death Valley, California

Valentine

Fierstein

White

2020

Geology

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Soft sediment deformation structures are common in fine-grained pyroclastic deposits and are often taken, along with other characteristics, to indicate that deposits were emplaced in a wet and cohesive state. At Ubehebe Crater (Death Valley, California, USA), deposits were emplaced by multiple explosions, both directly from pyroclastic surges and by rapid remobilization of fresh, fine-ash-rich deposits off steep slopes as local granular flows. With the exception of the soft sediment deformation structures themselves, there is no evidence of wet deposition. We conclude that deformation was a result of destabilization of fresh, fine-grained deposits with elevated pore-gas pressure and dry cohesive forces. Soft sediment deformation alone is not sufficient to determine whether parent pyroclastic surges contained liquid water and caused wet deposition of strata.

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

“…Folded structures (e.g., Figs. 3C and 3D) were interpreted to have formed during slumping of "wet sediment" (Douillet et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Soft sediment deformation in dry pyroclastic deposits at Ubehebe Crater, Death Valley, California

Valentine

Fierstein

White

2020

Geology

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“…Such "shark fins" are found to be preceded upstream by a "ploughed zone" suggesting a downstream migration. They were thus interpreted as shear horizons related to traction carpets on lee sides (Douillet et al 2015). More than 200 shark fins were analyzed and are the focus of the companion manuscript (Douillet et al sub).…”

Section: Overturned Shark Fin Structuresmentioning

confidence: 99%

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)

Douillet¹,

Bernard²,

Bouysson³

et al. 2018

Preprint

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Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid-turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss-face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive-based backset beds are evidenced. Recurrent trains of sub- vertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse-grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow-perpendicular and flow-parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope-influenced saltation; (iii) truncative bursts; and (iv) granular-based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude-supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and ‘chute and pools’ can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as Görtler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre-existing morphology. Quantification of near-bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0.30 m.s-1 (equivalent to pure wind velocity of 6 to 8 m.s-1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s-1.

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Event stratigraphy and emplacement mechanisms of the last major caldera eruption on Sete Cidades Volcano (São Miguel, Azores): the 16 ka Santa Bárbara Formation

et al. 2018

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Syn-eruptive, soft-sediment deformation of deposits from dilute pyroclastic density current: triggers from granular shear, dynamic pore pressure, ballistic impacts and shock waves

Abstract: Abstract. Soft-sediment deformation structures can provide valuable information about the conditions of parent flows, the sediment state and the surrounding environment.

Cited by 26 publications

References 88 publications

Soft sediment deformation in dry pyroclastic deposits at Ubehebe Crater, Death Valley, California

Soft sediment deformation in dry pyroclastic deposits at Ubehebe Crater, Death Valley, California

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)

Event stratigraphy and emplacement mechanisms of the last major caldera eruption on Sete Cidades Volcano (São Miguel, Azores): the 16 ka Santa Bárbara Formation

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