Depressurization of fine powders in a shock tube and dynamics of fragmented magma in volcanic conduits

Cagnoli, B.; Бармин, А. А.; Melnik, Oleg; Sparks, R S J

doi:10.1016/s0012-821x(02)00952-4

Cited by 31 publications

(51 citation statements)

References 17 publications

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“…For our experiments, we assumed isothermal conditions due to the high heat capacity of the matrix skeleton and the intense heat transfer between the gas and the skeleton (Cagnoli et al, 2002;Mueller et al, 2005). However, the results are valid for adiabatic (isentropic) conditions as well, if the relationship in Equation 5 is scaled times 1/(γ -1), where γ is the specifi c heat ratio of the gas (1.67 in the case of argon).…”

Section: Resultsmentioning

confidence: 99%

Permeability control on magma fragmentation

Mueller

Scheu

Spieler³

et al. 2008

Geol

150

146

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Fragmentation of porous magma that is subject to gas overpressure is considered to be a crucial process in the generation of explosive volcanic eruptions. A decompressive event (e.g., rapid magma ascent, landslide, dome collapse) disrupts the stress equilibrium between the gas phase and the surrounding melt. When the gas in the pores is exposed to a pressure gradient, it may either fragment the surrounding magma or escape from the magma along an existing pathway of cracks and interconnected bubbles. Therefore, magma permeability can be a decisive parameter in determining if an eruption experiences fragmentation (i.e., whether it is explosive or effusive, or exhibits a temporal transition between the two eruptive styles). Despite the central role that gas permeability may play in the fragmentation of volcanic rocks, previous studies have not experimentally verifi ed or quantifi ed this infl uence. Based on a comprehensive database of combined permeability and fragmentation experiments, we show that high permeability substantially increases the overpressure required to fragment porous volcanic rocks. Our results allow us to deduce a fragmentation criterion that incorporates gas permeability as well as porosity and internal overpressure. This criterion implies that the energy required for fragmentation is less dependent on the actual pore geometry than on the way the void space is interconnected and, thus, on the contribution of permeable gas fl ow to decompression.

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Section: Resultsmentioning

confidence: 99%

Permeability control on magma fragmentation

Mueller

Scheu

Spieler³

et al. 2008

Geol

150

146

View full text Add to dashboard Cite

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“…Velocity fluctuations during individual Strombolian explosions have been previously reported and interpreted either as “organ pipe resonance” [ Chouet et al , 1974], or as the bursting of several discrete bubbles [ Ripepe et al , 1993; Harris and Ripepe , 2007; Scharff et al , 2008]. Velocity pulses may also reflect post‐fragmentation pressure fluctuations in the gas‐particle mixture rising in the conduit [ Cagnoli et al , 2002; Dartevelle and Valentine , 2007].…”

Section: Discussionmentioning

confidence: 99%

High‐speed imaging of Strombolian explosions: The ejection velocity of pyroclasts

Taddeucci

Scarlato

Capponi

et al. 2012

Geophysical Research Letters

108

130

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[1] Explosive volcanic eruptions are defined as the violent ejection of gas and hot fragments from a vent in the Earth's crust. Knowledge of ejection velocity is crucial for understanding and modeling relevant physical processes of an eruption, and yet direct measurements are still a difficult task with largely variable results. Here we apply pioneering high-speed imaging to measure the ejection velocity of pyroclasts from Strombolian explosive eruptions with an unparalleled temporal resolution. Measured supersonic velocities, up to 405 m/s, are twice higher than previously reported for such eruptions. Individual Strombolian explosions include multiple, sub-second-lasting ejection pulses characterized by an exponential decay of velocity. When fitted with an empirical model from shock-tube experiments literature, this decay allows constraining the length of the pressurized gas pockets responsible for the ejection pulses. These results directly impact eruption modeling and related hazard assessment, as well as the interpretation of geophysical signals from monitoring networks. Citation: Taddeucci, J

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“…A shock tube apparatus is used to fluidize packed beds of spheres sourced from a range of materials and with nitrogen gas as the working fluid, with a range of bed heights from 15 to 60 cm, bed width of 3.8 cm with a square geometry, sphere diameters in the range 125-1000 μm, final speeds of 15-60 m/s, and accelerations in excess of 150 g. In that apparatus, the timescale for pressure to drop by a factor of e is about 1 ms. In contrast, Cagnoli et al (2002) use smaller sphere diameters (38 and 95 μm) and smaller pressure drops (200-900 mbar), mobilised by sudden decompression of a dry air environment. In some of Anilkumar's experiments the bed of spheres rests on a solid base, in others it rests on a mesh with more high-pressure nitrogen below.…”

Section: Dust Experimentsmentioning

confidence: 99%

“…When smaller (38 and 95 μm diameter) spheres are used together with smaller pressure changes (Cagnoli et al, 2002), slabs are still seen when pressure differences are small, but are not as ubiquitous as in the work of Anilkumar 1(989). Only bubbles are observed at very small pressure differences; at larger values there is a bubbly region in the upper part of the sample, then a slab region between the bubbly region and the undisturbed base.…”

Section: Dust Experimentsmentioning

confidence: 99%