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Fluid dynamics study on dynamics of eruption clouds (particularly on the significance of fragmentation processes)

喷发云动力学的流体动力学研究（特别是破碎过程的重要性）

基本信息

批准号：
09640505
负责人：
KOYAGUCHI Takehiro
金额：
$ 2.11万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

项目摘要

Theoretical modeling of explosive eruptions and a method to estimate intensity of eruption from granulometric data are developed in this study.Two types of theoretical models are established. The first one is a model to described a steady magma flow through a volcanic conduit. The model predicts a new regime of magma ascent flow due to relative motion between liquid and gas phases. The results may explain diversity of eruption style of silicic to andesitic magmas. The second one is a numerical code to simulate the turbulent flow of volcanic plumes and spreading umbrella clouds. The model enable us to estimate intensity of explosive volcanic eruptions from the remote-sensing observations of the eruption clouds.The granulometric method is applied to the tephra-fall deposits from the Pinatubo 1991 eruption. The results show that more than 70 wt % of the total ejecta and 60 wt. % of the phenocrysts in erupted magma were highly fragmented to become a very fine particles (a few tens of micron or less in diameter), so that they are extensively dispersed in the atmosphere during the explosive eruption. The shape of fine glass and difference in initial size distribution between glass fragments and crystal fragments indicate that the main mechanism of fragmentation is coalescence of bubbles in the magma.The similar method are also applied to the ejecta of the Asama 1783 eruption and those of the Suwanose 1813 eruption. As a results, the sequence of the explosive eruption in the Asama 1783 eruption was successfully reconstructed.

本研究建立了爆炸喷发的理论模型和根据粒度数据估计喷发强度的方法。建立了两类理论模型。第一个是描述稳定的岩浆流经火山管道的模型。该模型预测了由于液体和气相之间的相对运动而产生的一种新的岩浆上升流动模式。这一结果可能解释了硅质岩浆对安山岩岩浆喷发方式的多样性。第二个是一个数值程序，用来模拟火山羽流和蔓延的伞状云的湍流。该模型使我们能够通过对喷发云的遥感观测来估计火山喷发的强度。颗粒计量学方法被应用于1991年皮纳图博喷发的火山喷发沉积。结果表明，喷发岩浆中70wt%以上的喷射物和60wt%以上的斑晶高度碎裂成极细的颗粒(直径几十微米或更小)，在爆炸喷发过程中广泛分散在大气中。细小玻璃的形状和玻璃碎片与晶体碎片初始粒度分布的差异表明，破碎的主要机制是岩浆中气泡的聚合。类似的方法也适用于Asama 1783年喷发和Suwanose 1813年喷发的喷发。成功地重建了阿萨马1783年喷发的爆发式喷发序列。