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Numerical simulation of nucleation, growth, and coalescence of bubbles in magma

Masatoshi Ohashi

Abstract

Vesicle textures in volcanic pyroclasts have been useful for understanding the subsurface vesiculation process in magma. However, it is not easy to interpret vesicle textures because they are time-integrated products of a complex sequence of nucleation, growth, and coalescence of bubbles in magma. Here, we developed a new numerical simulation of these three processes and investigated how bubble size distribution in magma evolved with decompression. The new model incorporated the unsteady feature of the diffusion profile around growing bubbles. This unsteady growth greatly reduces the supersaturation, which in turn decreases the bubble number density after decompression. The bubble number density predicted by our model is more consistent with the results of decompression experiments than a previous model assuming the steady diffusion profile. We also proposed a new coalescence kernel for growing bubbles, based on film drainage timescale. As bubble coalescence proceeds, the distribution of bubble size gradually gets wider. The width of bubble size distribution is comparable with the reported data of the decompression experiments. Contrary to previous simulations that required a long computational time of several hours, our new simulation requires only several tens of seconds. This kinetic model can be a powerful tool for assessing the nucleation, growth, and coalescence of bubbles in magma.