Work

The nucleation and growth of mixed H2O–CO2 bubbles in magmas

Year: 2026

Type: article

Abstract: Volcanic eruptions are driven by the nucleation and growth of gas bubbles that form when volatile species dissolved in magma become supersaturated. Previous models for bubble growth have focussed on H 2 O; however, CO 2 also plays a fundamental role in the nucleation and growth of gas bubbles. Here, we develop a numerical model to explore the nucleation and growth of bubbles containing both H 2 O and CO 2 in magma of arbitrary composition. Nucleation is modelled as a Poisson process using classical nucleation theory with composition-appropriate solubility models for the mixed H 2 O–CO 2 fluid. We find that CO 2 dramatically increases the depth of bubble nucleation compared with H 2 O-only systems; for a case-study rhyolite (Krafla, Iceland) CO 2 increases nucleation depth from 130 m (H 2 O-only) to 760 m if CO 2 is included (a factor of 6 increase in nucleation pressure); for a case-study basalt (Fagradalsfjall, Iceland), nucleation occurs at 13 km depth if CO 2 is included, but does not occur at all if H 2 O is the only volatile species. Post-nucleation growth of the bubbles is investigated by extending a ‘shell model’ to include CO 2 as well as H 2 O. The species are coupled via a mixed equation-of-state for the gas phase, introducing a co-dependence on their solubility that allows H 2 O to exsolve at greater depth when CO 2 is present. As a result, exsolution of a small volume of CO 2 can trigger the exsolution of a much larger volume of H 2 O, driving rapid, disequilibrium bubble growth. Our findings show that accounting for mixed H 2 O–CO 2 volatile compositions is essential for accurate modelling of magma ascent and eruption dynamics. • Numerical model for mixed H 2 O-CO 2 bubble nucleation and growth developed. • CO 2 shown to significantly increase nucleation pressure. • Disequilibrium degassing leaves geochemical signals in melt and gas phases.

Source: Journal of Volcanology and Geothermal Research

DOI: 10.1016/j.jvolgeores.2026.108538

Authors: Patrick Sullivan, Edward W. Llewellin, Fabian B. Wadsworth, Simone Colucci, Halim Kusumaatmaja

Institutions: Durham University, Ludwig-Maximilians-Universität München, Istituto Nazionale di Geofisica e Vulcanologia, INGV Sezione di Pisa, University of Edinburgh

Language: English

Topic: Geological and Geochemical Analysis

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

SDG: Climate action

Open Access status: hybrid

Estimated APC paid: $3,420