Pressure changes associated with the ascent and bursting of gas slugs in liquid-filled vertical and inclined conduits.
TL;DR: In this article, two-phase flow experiments have been carried out in vertical and inclined pipes with both single gas slugs and a continuously supplied gas phase, and the experimental pressure data support previous theoretical analyses of oscillatory sources in ascending slugs as the slugs approach the surface and burst.
About: This article is published in Journal of Volcanology and Geothermal Research.The article was published on 2004-01-15. It has received 127 citations till now. The article focuses on the topics: Slug flow & Gas slug.
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TL;DR: In the field of volcano seismology, a wide variety of signals originating in the transport of magma and related hydrothermal fluids and their interaction with solid rock have been studied as discussed by the authors.
366 citations
TL;DR: Basaltic pyroclastic volcanism takes place over a range of scales and styles, from weak discrete Strombolian explosions (∼10 2 −10 3 ) to Plinian eruptions of moderate intensity (10 7 −10 8 ǫ −1 ). Recent well-documented historical eruptions from Etna, Kīlauea and Stromboli typify this diversity as discussed by the authors.
Abstract: Basaltic pyroclastic volcanism takes place over a range of scales and styles, from weak discrete Strombolian explosions (∼10 2 –10 3 kg s −1 ) to Plinian eruptions of moderate intensity (10 7 –10 8 kg s −1 ). Recent well-documented historical eruptions from Etna, Kīlauea and Stromboli typify this diversity. Etna is Europe's largest and most voluminously productive volcano with an extraordinary level and diversity of Strombolian to subplinian activity since 1990. Kīlauea, the reference volcano for Hawaiian fountaining, has four recent eruptions with high fountaining (>400 m) activity in 1959, 1960, 1969 (–1974) and 1983–1986 (–2008); other summit (1971, 1974, 1982) and flank eruptions have been characterized by low fountaining activity. Stromboli is the type location for mildly explosive Strombolian eruptions, and from 1999 to 2008 these persisted at a rate of ca. 9 per hour, briefly interrupted in 2003 and 2007 by vigorous paroxysmal eruptions. Several properties of basaltic pyroclastic deposits described here, such as bed geometry, grain size, clast morphology and vesicularity, and crystal content are keys to understand the dynamics of the parent eruptions. The lack of clear correlations between eruption rate and style, as well as observed rapid fluctuations in eruptive behavior, point to the likelihood of eruption style being moderated by differences in the fluid dynamics of magma and gas ascent and the mechanism by which the erupting magma fragments. In all cases, the erupting magma consists of a mixture of melt and gaseous bubbles. The depth and rate of degassing, melt rheology, bubble rise and coalescence rates, and extent of syn-eruptive microlite growth define complex feedbacks that permit reversible shifts between fragmentation mechanisms and in eruption style and intensity. However, many basaltic explosive eruptions end after an irreversible shift to open-system outgassing and microlite crystallization in melt within the conduit. Clearer understanding of the factors promoting this diversity of basaltic pyroclastic eruptions is of fundamental importance in order to improve understanding of the range of behaviors of these volcanoes and assess hazards of future explosive events at basaltic volcanoes. The three volcanoes used for this review are the sites of large and growing volcano-tourism operations and there is a public need both for better knowledge of the volcanoes’ behavior and improved forecasting of the likely course of future eruptions.
189 citations
Cites background from "Pressure changes associated with th..."
...Both processes may be enhanced or facilitated at geometric asperities within the magmatic plumbing system where bubbles can accumulate (e.g., James et al., 2004)....
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...In both cases, slug formation can be enhanced or facilitated at geometric asperities within the magmatic plumbing system (James et al., 2004)....
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...Conduit geometry may also play an important role in facilitating bubble accumulation, potentially of importance in Strombolian style eruptions (e.g., Ripepe and Gordeev, 1999; James et al., 2004, 2006; Menand and Phillips, 2007)....
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...…bubbles may rise and/or accumulate elsewhere in the conduit system (e.g., Wilson, 1980; Wilson and Head, 1981; Vergniolle and Jaupart, 1986, 1990; Jaupart and Vergniolle, 1988, 1989; Parfitt, 2004; Parfitt and Wilson, 1995; Parfitt et al., 1995; James et al., 2004; Menand and Phillips, 2007)....
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..., 1993); and (4) buoyantly ascending decoupled bubbles may rise and/or accumulate elsewhere in the conduit system (e.g., Wilson, 1980; Wilson and Head, 1981; Vergniolle and Jaupart, 1986, 1990; Jaupart and Vergniolle, 1988, 1989; Parfitt, 2004; Parfitt and Wilson, 1995; Parfitt et al., 1995; James et al., 2004; Menand and Phillips, 2007)....
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TL;DR: In this article, microtextural characteristics of fresh ejecta from Stromboli volcano were examined from three periods of differing eruption style and intensity in 2002, 2003, and 2004.
Abstract: Microtextural characteristics of fresh ejecta from Stromboli volcano were examined from three periods of differing eruption style and intensity in 2002. Activity shifted from relatively weak and infrequent ash-charged explosions during January through May into two broad cycles of waxing activity in June through late September, and late September through December, followed by the onset on 28 December of the 2002/2003 effusive eruption. Analyzed sets of lapilli from May, September/October, and 28 December show contrasts in the physical properties of magma resident in the shallow conduit during this range of activity. Three distinct textures are observed among the analyzed pyroclasts: low density (LD) with an abundance of subspherical bubbles, the presence of large, irregularly shaped bubbles, and a light-to-transparent glass matrix; transitional texture (TT) with an intermediate number of subspherical bubbles, a high frequency of large, irregularly-shaped bubbles, and a honey colored glass matrix; and high density (HD) with sparse relatively small bubbles, conspicuous large irregular bubbles, and a dark glass matrix. Observational and quantitative data (density, vesicle size) indicate that these textures are linked through variable residence time in Stromboli’s shallow conduit, with an ongoing evolution from LD to HD magma. Calculations suggest that residual LD magma will evolve to HD texture in a period of hours to days. Contrasting amounts of the LD, TT, and HD magmas are present in each sample, with the most TT in May, the most LD in September/October, and the most HD in December. This implies that the shallow magma had a different rheology at each collection period. The viscosity of LD and HD magmas are calculated to be in the range of 2,000 to 2,600 and 3,000 to 5,000 Pa s, respectively, which, with their changing proportions, must have implications for rates of bubble slug ascent and processes of fragmentation. This study suggests that an increasing maturity of magma in Stromboli’s shallow conduit (with resultant increase in viscosity) feeds back to reduce the intensity of explosions, whereas a steady flux of LD magma favors more powerful explosions.
163 citations
Cites background from "Pressure changes associated with th..."
...At Stromboli, seismic data indicate that rapid bubble/slug expansion ( James et al. 2004 ) begins ∼250 m below the active crater terrace (Chouet et al. 2003; Ripepe et al. 2005)....
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TL;DR: Results from a laboratory experiment in which basalt from Mount Etna volcano (Italy) was deformed and fractured triggered many low-frequency events, analogous to volcanic long-period seismicity.
Abstract: The physical processes generating seismicity within volcanic edifices are highly complex and not fully understood. We report results from a laboratory experiment in which basalt from Mount Etna volcano (Italy) was deformed and fractured. The experiment was monitored with an array of transducers around the sample to permit full-waveform capture, location, and analysis of microseismic events. Rapid post-failure decompression of the water-filled pore volume and damage zone triggered many low-frequency events, analogous to volcanic long-period seismicity. The low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample; these events exhibited a weak component of shear (double-couple) slip, consistent with fluid-driven events occurring beneath active volcanoes.
148 citations
TL;DR: In this paper, the authors present a direct link between gas flux, magma volume flux, and seismicity, supporting a gas driven model whereby the balance between the gas flux and gas overpressure determines whether the system will support effusive or explosive activity.
Abstract: The persistent explosive activity of Stromboli volcano (Italy) ceased in December 2002 and correlated with the onset of a seven-month-long effusive eruption on the volcano flank from new vents that opened just below the summit craters. We intensively monitored this effusive event, collecting and interpreting, in real time, an extensive multiparametric geophysical data set. The resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical Strombolian activity. We present a direct link between gas flux, magma volume flux, and seismicity, supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity. This insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity.
136 citations
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01 Jun 1978TL;DR: In this paper, the authors evaluated the applicability of the standard κ-ϵ equations and other turbulence models with respect to their applicability in swirling, recirculating flows.
Abstract: The standard κ-ϵ equations and other turbulence models are evaluated with respect to their applicability in swirling, recirculating flows. The turbulence models are formulated on the basis of two separate viewpoints. The first perspective assumes that an isotropic eddy viscosity and the modified Boussinesq hypothesis adequately describe the stress distributions, and that the source of predictive error is a consequence of the modeled terms in the κ-ϵ equations. Both stabilizing and destabilizing Richardson number corrections are incorporated to investigate this line of reasoning. A second viewpoint proposes that the eddy viscosity approach is inherently inadequate and that a redistribution of the stress magnitudes is necessary. Investigation of higher-order closure is pursued on the level of an algebraic stress closure. Various turbulence model predictions are compared with experimental data from a variety of isothermal, confined studies. Supportive swirl comparisons are also performed for a laminar flow case, as well as reacting flow cases. Parallel predictions or contributions from other sources are also consulted where appropriate. Predictive accuracy was found to be a partial function of inlet boundary conditions and numerical diffusion. Despite prediction sensitivity to inlet conditions and numerics, the data comparisons delineate the relative advantages and disadvantages of the various modifications. Possible research avenues in the area of computational modeling of strongly swirling, recirculating flows are reviewed and discussed.
5,396 citations
TL;DR: At an active volcano, long-period seismicity reflects pressure fluctuations resulting from unsteady mass transport in the sub-surface plumbing system, and hence provides a glimpse of the internal dynamics of the volcanic edifice as mentioned in this paper.
Abstract: At an active volcano, long-period seismicity (with typical periods in the range 02–2 s) reflects pressure fluctuations resulting from unsteady mass transport in the sub-surface plumbing system, and hence provides a glimpse of the internal dynamics of the volcanic edifice When this activity occurs at shallow depths, it may signal the pressure-induced disruption of the steam-dominated region of the volcano, and can accordingly be a useful indicator of impending eruption
832 citations
TL;DR: In this article, two source centroids are identified, each representative of the distinct event types associated with explosive eruptions from two different vents, and the two sources that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents, respectively.
Abstract: [1] Seismic data recorded in the 2–30 s band at Stromboli Volcano, Italy, are analyzed to quantify the source mechanisms of Strombolian explosions during September 1997. To determine the source-centroid location and source mechanism, we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account. Two source centroids are identified, each representative of the distinct event types associated with explosive eruptions from two different vents. The observed waveforms are well reproduced by our inversion, and the two source centroids that best fit the data are offset 220 and 260 m beneath and � 160 m northwest of the active vents. The source mechanisms include both moment-tensor and single-force components. The principal axes of the moment tensor have amplitude ratios 1:1:2, which can be interpreted as representative of a crack, if one assumes the rock matrix at the source to have a Poisson ratio n = 1/3, a value appropriate for hot rock. Both imaged cracks dip � 60� to the northwest and strike northeast–southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness, as expressed by lineaments, dikes, and brittle structures. For our data set, the volume changes estimated from the moments are � 200 m 3 for the largest explosion from each vent. Together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 N, consistent with the inferred movement of the magma column perched above the source centroid in response to the piston-like rise of a slug of gas in the conduit. INDEX TERMS: 7215 Seismology: Earthquake parameters; 7280 Seismology: Volcano seismology (8419); 8414 Volcanology: Eruption mechanisms; KEYWORDS: very-long-period seismicity, moment tensor inversions, eruption mehanics
363 citations
TL;DR: In this article, the authors reviewed the modelling efforts on the flow patterns published in the last 30 years with relatively more focus on the last 10 years, focusing on cylindrical bubble columns where results on flow pattern could be extended to the design.
362 citations