Bubble Formation in Magma

Abstract

Volcanic eruptions are driven by bubbles that form when volatile species exsolve from magma. The conditions under which bubbles form depend mainly on magma composition, volatile concentration, presence of crystals, and magma decompression rate. These are all predicated on the mechanism by which volatiles exsolve from the melt to form bubbles. We critically review the known or inferred mechanisms of bubble formation in magmas: homogeneous nucleation, heterogeneous nucleation on crystal surfaces, and spontaneous phase separation (spinodal decomposition). We propose a general approach for calculating bubble nucleation rates as the sum of the contributions from homogeneous and heterogeneous nucleation, suggesting that nucleation may not be limited to a single mechanism prior to eruption. We identify three major challenges in which further experimental, analytical, and theoretical work is required to permit the development of a general model for bubble formation under natural eruption conditions. ▪ We review the mechanisms of bubble formation in magma and summarize the conditions under which the various mechanisms are understood to operate. ▪ Bubble formation mechanisms may evolve throughout magma ascent as conditions change such that bubbles may form simultaneously and sequentially via more than one mechanism. ▪ Contributions from both homogeneous nucleation and heterogeneous nucleation on multiphase crystal phases can be captured via a single equation. ▪ Future work should focus on constraining macroscopic surface tension, characterizing the microphysics, and developing a general framework for modeling bubble formation, via all mechanisms, over natural magma ascent pathways. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 51 is May 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The physics of dancing peanuts in beer

“…the difference between the ambient pressure in the liquid and the saturation pressure) [13]. By contrast with homogeneous nucleation, heterogeneous nucleation is facilitated by an external surface and consequently the affinity between the new gaseous phase and the solid surface is of importance [13,15]. Based on CNT, Δ G c isnormalΔGnormalc=true016πσ33normalΔP2α, where σ is the surface tension and α is a geometric parameter that is defined as a function of the contact angle ψ [14]:α=true0false(2−cos⁡(ψ)false)false(1+cos⁡false(ψfalse)false)24.…”

“…Most beers, including lagers, involve CO 2 as the dominant dissolved gas species [5]. When beers are opened or poured from a tap, they decompress, which induces supersaturation of CO 2 and bubble nucleation [11][12][13][14][15]. Classical nucleation theory (CNT) [16] predicts homogeneous nucleation in a liquid and considers that nucleation takes place when molecules of the separating phase form a cluster larger than the critical radius.…”

“…Open Sci. 10: 230376 nucleation, heterogeneous nucleation is facilitated by an external surface and consequently the affinity between the new gaseous phase and the solid surface is of importance [13,15]. Based on CNT, ΔG c is…”

Evaluating the Role of Titanomagnetite in Bubble Nucleation: Novel Applications of Low Temperature Magnetic Analysis and Textural Characterization of Rhyolite Pumice and Obsidian From Glass Mountain, California

“…Magnetic techniques allowed us to access the nm‐scale and could prove essential in re‐assessing the respective abundances of oxides and vesicles in samples from other eruptions of differing styles and magma compositions (e.g., Burgisser et al., 2020). Whether fully heterogeneous nucleation dominates in nature or whether nucleation is, in certain cases, hybrid (both heterogeneous and homogeneous, e.g., Gardner et al., 2023) will best be ascertained by integrating traditional sample imaging techniques and magnetic measurements. Current applications of X‐ray computed tomography can successfully detect micron scale objects and provide 3D textural context (e.g., Giachetti et al., 2011; Gualda & Rivers, 2006), whereas magnetic methodologies excel at the detection of nm scale oxides.…”

The effects of oxygen fugacity and sulfur on the pressure of vapor-saturation of magma

“…Hence, these calculations assume the melt is saturated with a vapor -if the melt is not vapor-saturated, the calculated P represents a minimum. At a lower P than P v sat , melt with the assumed concentrations of volatiles is supersaturated with respect to vapor and the melt is metastable (or potentially unstable if sufficiently supersaturated; e.g., Allabar and Nowak 2018;Sahagian and Carley 2020;Gardner et al 2022). Given sufficient time, a vapor phase will exsolve from the supersaturated melt, reducing the volatile concentration of the melt such that equilibrium is achieved (i.e., such that equation ( 1) is satisfied at the fixed P, T, and bulk composition of the system).…”