An expansion-coalescence model to track gas bubble populations in magmas

作者：Mancini Simona; Forestier Coste Louis; Burgisser Alain^*; James Francois; Castro Jonathan

来源：Journal of Volcanology and Geothermal Research, 2016, 313: 44-58.

DOI：10.1016/j.jvolgeores.2016.01.016

• Bubble size distribution
• Rhyolite
• Expansion
• Gas bubbles
• Coalescence
• Kinetic equation

We propose a kinetic model that statistically describes the growth by decompression, exsolution and coalescence of a polydisperse population of gas bubbles in a silicate melt. The model is homogeneous in space and its main variable is a distribution function representing the probability to find a bubble of volume v and mass mat time t. The volume and mass growth rates are described by a simplification of the classical monodisperse bubble growth model. This simplification, which shortens computational time, removes the coupling between mass evolution and an advection-diffusion equation describing the behavior of the volatile concentration in the melt. We formulate three coalescence mechanisms: thinning of the inter-bubble planar films, film deformation by differential bubble pressure, and buoyancy-driven collision. Numerical simulations based on a semi-implicit numerical scheme show a good agreement between the coalescence-free runs and the monodisperse runs. When coalescence is introduced, numerical results show that coalescence kernels based on different physical mechanisms yield distinct evolutions of the size distributions. A preliminary comparison between runs and experimental data suggests a qualitative match of two out of the three proposed kernels. This kinetic model is thus a powerful tool that can help in assessing how bubble growth and coalescence occur in magmas.

• 出版日期2016-3-1