Valve-like dynamics of gas flow through a packed crystal mush and cyclic strombolian explosions

Abstract

Strombolian volcanic explosions are commonly attributed to the rise and burst of conduit-filling gas slugs. The magmas associated with strombolian activity, however, are typically not only volatile-rich but also highly crystalline, with mush regions in the shallow plumbing system, where an exsolved volatile phase may also be abundant. Through analogue experiments, we explore a new mechanism to form gas slugs and strombolian explosions. A steady flux of gas is supplied to the base of a particle-rich liquid layer, generating a localised gas intrusion, which initially grows through plastic deformation. Once the pressure in the intrusion overcomes the effective tensile strength of the particle pack, a localised channel opens, allowing gas to propagate upwards. As the pressure in the intrusion falls, the gas pocket collapses. The continued supply of gas leads to the formation of a new intrusion, and the cycle repeats. With higher gas fluxes, continuous channelised gas flow occurs. Highly crystalline shallow portions of basaltic conduits may act as a flow valve, transforming a steady gas flux into a series of discrete gas slugs which cause explosions.

Origin of Shallow Volcanic Tremor: The Dynamics of Gas Pockets Trapped Beneath Thin Permeable Media

“…A second (and end‐member) option is that gas supply is highly periodic, a possibility proposed by several authors (e.g., Lesage et al, ; Ripepe et al, ) and that generates harmonic tremor in our thin‐caps model through a Dirac comb effect (Figures d, e, and f). Periodic gas supply could be controlled by rectified diffusion (Brodsky et al, ); the flow of bubbles through granular suspensions (i.e., crystal‐rich magma; Barth et al, ); the collapse of critically unstable bubble rafts, foams, or viscoelastic layers formed at the top of magma columns (Ritacco et al, ; Spina et al, ; Vidal et al, ); natural self‐organization of bubbles to produce gas waves (Manga, ; Michaut et al, ); and the coupling between gas exsolution and the pressure changes occurring below the permeable cap, as motivated by experiments performed with slightly open soda bottles (Hellweg, ; Soltzberg et al, ). These mechanisms may play an important role in generating periodic gas emissions in persistently outgassing volcanoes (e.g., Girona, Costa, Taisne, et al, ; Tamburello et al, ), although it is unclear whether they can supply gas at a sufficient degree of periodicity to produce a Dirac comb effect (Hagerty et al, ; Powell & Neuberg, ).…”

A continuum model of multi-phase reactive transport in igneous systems

“…Experiments show that this last stage is prone to flow localization and tipping-point behaviors (e.g., Oppenheimer et al, 2015;Barth et al, 2019). To date, few igneous process models have included a third volatile phase.…”

Modeling water exsolution from a growing and solidifying felsic magma body

“…It has been shown experimentally (Barth et al, 2019;Holtzman et al, 2012;Oppenheimer et al, 2015;Varas et al, 2015) and numerically (Parmigiani et al, 2017) that mushes are favorable to the formation of permeable pathways and gas migration. For crystal volume fractions in the range 0.4-0.7, crystals form a connected network with gas and melt confined in the interstitial space.…”