Geological implications and applications of high-velocity two-phase flow experiments

Anilkumar, A. V.; Sparks, R. S. J.; Sturtevant, B.

doi:10.1016/0377-0273(93)90056-w

Cited by 66 publications

(63 citation statements)

References 33 publications

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“…The potential influence of conduit flow processes Models for conduit flow and fragmentation based on analog experiments and simulations (Anilkumar et al 1993;Mader et al 1994Mader et al , 1996Mader et al , 1997Papale 1998) show significant inhomogeneity of the two-phase flow with the development of regions of relatively high and low particle concentration during early expansion. Such inhomogeneities seem likely to have been inherited by the 1912 plume, and are potentially the explanation for the irregular patterns of proximal sedimentation.…”

Section: Implications For Eruption Column Modelsmentioning

confidence: 99%

Complex proximal deposition during the Plinian eruptions of 1912 at Novarupta, Alaska

Houghton

Wilson

Fierstein

et al. 2004

Bulletin of Volcanology

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Proximal (<3 km) deposits from episodes II and III of the 60-h-long Novarupta 1912 eruption exhibit a very complex stratigraphy, the result of at least four transport regimes and diverse depositional mechanisms. They contrast with the relatively simple stratigraphy (and inferred emplacement mechanisms) for the previously documented, better known, medial-distal fall deposits and the Valley of Ten Thousand Smokes ignimbrite. The proximal products include alternations and mixtures of both locally and regionally dispersed fall ejecta, and numerous thin complex deposits of pyroclastic density currents (PDCs) with no regional analogs. The locally dispersed component of the fall deposits forms sectorconfined wedges of material whose thicknesses halve radially from and concentrically about the vent over distances of 100-300 m (cf. several kilometers for the medial-distal fall deposits). This locally dispersed fall material (and many of the associated PDC deposits) is rich in andesitic and banded pumices and richer in shallow-derived wall-rock lithics in comparison with the coeval medial fall units of almost entirely dacitic composition. There are no marked contrasts in grain size in the near-vent deposits, however, between locally and widely dispersed beds, and all samples of the proximal fall deposits plot as a simple continuation of grain size trends for medial-distal samples. Associated PDC deposits form a spectrum of facies from fines-poor, avalanched beds through thin-bedded, landscape-mantling beds to channelized lobes of pumice-block-rich ignimbrite. The origins of the Novarupta near-vent deposits are considered within a spectrum of four transport regimes: (1) sustained buoyant plume, (2) fountaining with co-current flow, (3) fountaining with counter-current flow, and (4) direct lateral ejection. The Novarupta deposits suggest a model where buoyant, stable, regime-1 plumes characterized most of episodes II and III, but were accompanied by transient and variable partitioning of clasts into the other three regimes. Only one short period of vent blockage and cessation of the Plinian plume occurred, separating episodes II and III, which was followed by a single PDC interpreted as an overpressured "blast" involving direct lateral ejection. In contrast, regimes 2 and 3 were reflected by spasmodic sedimentation from the margins of the jet and perhaps lower plume, which were being strongly affected by short-lived instabilities. These instabilities in turn are inferred to be associated with heterogeneities in the mixture of gas and pyroclasts emerging from the vent. Of the parameters that control explosive eruptive behavior, only such sudden and asymmetrical changes in the particle concentration could operate on time scales sufficiently short to explain the rapid changes in the proximal 1912 products.

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Section: Implications For Eruption Column Modelsmentioning

confidence: 99%

Complex proximal deposition during the Plinian eruptions of 1912 at Novarupta, Alaska

Houghton

Wilson

Fierstein

et al. 2004

Bulletin of Volcanology

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“…The foamy material between the partings then separated to form tabular clasts. Shock tube experiments have shown that a fragmentation wave which propagates down into a volcanic conduit after rapid decompression can produce such tabular clasts (Anilkumar et al 1993;Dingwell 1996, 2000). We have observed such clast shapes in tephra from the 1994 eruption of the Kluchevskoy volcano, and in fallout pumice from vulcanian eruptions of the Soufriere Hills volcano, Montserrat (Druitt et al 2002).…”

Section: Clast Morphologymentioning

confidence: 99%

Pyroclastic surges and flows from the 8-10 May 1997 explosive eruption of Bezymianny volcano, Kamchatka, Russia

Belousov

Voight

Belousova

et al. 2002

Bulletin of Volcanology

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The 8-10 May 1997 eruption of Bezymianny volcano began with extrusion of a crystallized plug from the vent in the upper part of the dome. Progressive gravitational collapses of the plug caused decompression of highly crystalline magma in the upper conduit, leading at 13:12 local time on 9 May to a powerful, vertical Vulcanian explosion. The dense pyroclastic mixture collapsed in boil-over style to generate a pyroclastic surge which was focused toward the southeast by the steepwalled, 1956 horseshoe-shaped crater. This surge, with a temperature <200°C, covered an elliptical area >30 km 2 with deposits as much as 30 cm thick and extending 7 km from the vent. The surge deposits comprised massive to vaguely laminated, gravelly sand (Md -1.2 to 3.7φ; sorting 1.2 to 3φ) of poorly vesiculated andesite (mean density 1.82 g cm -3 ; vesicularity 30 vol%; SiO 2 content ~58.0 wt%). The deposits, with a volume of 5-15×10 6 m 3 , became finer grained and better sorted with distance; the maximal diameter of juvenile clasts decreased from 46 to 4 cm. The transport and deposition of the surge over a snowy landscape generated extensive lahars which traveled >30 km. Immediately following the surge, semi-vesiculated block-and-ash flows were emplaced as far as 4.7 km from the vent. Over time the juvenile lava in clasts of these flows became progressively less crystallized, apparently more silicic (59.0 to 59.9 wt% SiO 2 ) and more vesiculated (density 1.64 to 1.12 g cm -3 ; vesicularity 37 to 57 vol%). At this stage the eruption showed transitional behavior, with mass divided between collapsing fountain and buoyant column. The youngest pumice-and-ash flows were accompanied by a sustained sub-Plinian eruption column ~14 km high, from which platy fallout clasts were deposited (~59.7% SiO 2 ; density 1.09 g cm -3 ; vesicularity 58 vol%). The explosive activity lasted about 37 min and produced a total of ~0.026 km 3 dense rock equivalent of magma, with an average discharge of ~1.2×10 4 m 3 s -1 . A lava flow 200 m long terminated the eruption. The evolutionary succession of different eruptive styles during the explosive eruption was caused by vertical gradients in crystallization and volatile content of the conduit magma, which produced significant changes in the properties of the erupting mixture.

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“…The density discontinuities reproduced in experiments of fluidization [17] and high-speed two-phase flow decompression [18], as well as the marked facies diversity of the deposits, are cited in support of a discontinuity between flow and surge.…”

Section: Introductionmentioning

confidence: 99%

Reconciling pyroclastic flow and surge: the multiphase physics of pyroclastic density currents

Burgisser

Bergantz

2002

Earth and Planetary Science Letters

128

100

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Two end-member types of pyroclastic density current are commonly recognized: pyroclastic surges are dilute currents in which particles are carried in turbulent suspension and pyroclastic flows are highly concentrated flows. We provide scaling relations that unify these end-members and derive a segregation mechanism into basal concentrated flow and overriding dilute cloud based on the Stokes number (S T ), the Stability factor (Σ Τ ) and the Dense-Dilute condition (D D ).We recognize five types of particle behaviors within a fluid eddy as a function of S T and Σ T : (1) particles sediment from the eddy, (2) particles are preferentially settled out during the downward motion of the eddy, but can be carried during its upward motion, (3) particles concentrate on the periphery of the eddy, (4) particles settling can be delayed or "fast-tracked" as a function of the eddy spatial distribution, and (5) particles remain homogeneously distributed within the eddy. We extend these concepts to a fully turbulent flow by using a prototype of kinetic energy distribution within a full eddy spectrum and demonstrate that the presence of different particle sizes leads to the density stratification of the current. This stratification may favor particle interactions in the basal part of the flow and D D determines whether the flow is dense or dilute. Using only intrinsic characteristics of the current, our model explains the discontinuous features between pyroclastic flows and surges while conserving the concept of a continuous spectrum of density currents.

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Geological implications and applications of high-velocity two-phase flow experiments

Cited by 66 publications

References 33 publications

Complex proximal deposition during the Plinian eruptions of 1912 at Novarupta, Alaska

Complex proximal deposition during the Plinian eruptions of 1912 at Novarupta, Alaska

Pyroclastic surges and flows from the 8-10 May 1997 explosive eruption of Bezymianny volcano, Kamchatka, Russia

Reconciling pyroclastic flow and surge: the multiphase physics of pyroclastic density currents

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