論文

査読有り
2008年11月20日

Vesiculation and crystallization under instantaneous decompression: Numerical study and comparison with laboratory experiments

Journal of Volcanology and Geothermal Research
  • A. Toramaru
  • ,
  • T. Miwa

177
4
開始ページ
983
終了ページ
996
記述言語
英語
掲載種別
研究論文(学術雑誌)
DOI
10.1016/j.jvolgeores.2008.07.013
出版者・発行元
Elsevier BV

Vesiculation and crystallization in ascending magmas are key processes that control the eruption behavior, and they interplay each other through the water exsolution process. We conducted a numerical study in order to quantitatively understand the water exsolution and crystallization processes in natural eruptions (decompression history is unknown) and in laboratory experiments (the amount of decompression is constant with time). The numerical results, which take into account homogeneous or heterogeneous nucleation and growth of bubbles with varying diffusivity of water, viscosity, and the amount of decompression, provide a quantitative understanding of their control on bubble formation and water exsolution in the constant amount of decompression. The bubble nucleation in the homogeneous nucleation can be divided into two regimes - the diffusion control regime and viscosity control regime - depending on the modified Peclet number and the effective supersaturation. In the cases of both homogeneous and heterogeneous nucleations, the bubble growth is controlled by diffusion or viscosity, depending on the modified Peclet number and bubble number density. The water exsolution rate, which is controlled by the modified Peclet number in the viscosity control regime and by the bubble number density and diffusive driving force in the diffusion control regime, acts as an effective cooling rate in a decompression-induced crystallization process. A comparison of the numerical results with the results of laboratory experiments suggests that water exsolution proceeds by the diffusion-limited growth of bubbles under disequilibrium vesiculation through the heterogeneous nucleation of bubbles, and this in turn controls the crystallization kinetics of microlite with the homogeneous nucleation of microlite and the diffusion-limited growth of crystal. The several orders of variation of microlite number density with the amount of decompression in laboratory experiments can be interpreted as the effect of the amount of decompression on the driving force for the diffusive bubble growth that controls the water exsolution rate. © 2008 Elsevier B.V. All rights reserved.

リンク情報
DOI
https://doi.org/10.1016/j.jvolgeores.2008.07.013

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