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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Temporal variation in volcanic ash texture during a vulcanian eruption at the Sakurajima volcano, Japan
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Temporal variation in volcanic ash texture during a vulcanian eruption at the Sakurajima volcano, Japan

机译：日本樱岛火山火山喷发期间火山灰质地的时间变化

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摘要

We discuss the process of vulcanian eruptions on the basis of temporal variation of the texture of andesitic volcanic ash ejected from the Sakurajima volcano, Japan. Falling ash samples were collected every 2-50 min for petrological analysis. These ash samples contained juvenile particles, altered rock fragments, and fragments of crystals; here, we subdivide the juvenile particles into blocky, vesicular, and fluidal particles. Because the crystallinities of the vesicular and fluidal particles are lower than those of the blocky particles, we refer to the vesicular and fluidal particles as low-crystallinity particles (LCPs) and the blocky particles as high-crystallinity particles (HCPs). The temporal variation observed in ash texture reveals that the ratio of LCPs to HCPs (LCP/HCP) was small at the initiation of the eruption and increased as the eruption progressed. The higher microlite crystal-linity in the HCPs indicates crystallization under lower pressures for longer durations relative to the LCP magma. The increase of the LCP/HCP ratio during a single vulcanian eruption suggests that the emission of less viscous gas-rich magma under a cap rock increases as the eruption progresses. Such temporal variation in ash texture reflects the transition from a sudden explosion to continuous ash emission during a vulcanian eruption.
机译：我们根据从日本樱岛火山喷出的安第斯火山灰质地的时间变化来讨论火山爆发的过程。每2-50分钟收集一次飞灰样品，用于岩石学分析。这些灰烬样品中含有少年颗粒，蚀变的岩石碎片和晶体碎片。在这里，我们将少年颗粒细分为块状，囊状和流体性颗粒。因为囊泡和流体颗粒的结晶度低于块状颗粒的结晶度，所以我们将囊泡和流体颗粒称为低结晶度颗粒（LCP），将块状颗粒称为高结晶度颗粒（HCP）。在灰烬质地中观察到的时间变化表明，在喷发开始时，LCP与HCP的比例（LCP / HCP）很小，并且随着喷发的进行而增加。相对于LCP岩浆，HCP中较高的微晶结晶度表明在较低的压力下结晶的时间更长。在一次火山喷发过程中，LCP / HCP比值的增加表明，随着喷发的进行，盖层下粘性较小的富气岩浆的排放量增加。灰烬质地的这种时间变化反映了在火山爆发期间从突然爆炸到连续排放灰烬的过渡。

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