Study of the groundmass textures of volcanic products from Asama volcano and its implications for prediction of eruption.

研究浅间火山火山产物的基质结构及其对喷发预测的影响。

基本信息

批准号：
17540435
负责人：
MIYAKE Yasuyuki
金额：
$ 2.3万
依托单位：
SHINSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-17540435/
关键词：
Asama volcano vulcanian eruption pumice scoria volcanic bomb water content crystal size distribution excess pressure 津間火山

项目摘要

Asama volcano, central Japan was active during September to December, 2004. Among its several eruptions, vulcanian eruptions of Sept 1st. and Sept 23rd. were relatively intensive. We described the ascent and crystallization process of the magma during these three weeks as follows. Before Sept. 1st, a column of new magma had risen into the pre existing andesite body beneath the crater floor. On Sept.1st, the built up gas pressure surpassed the tensile strength of the andesite body to result in a vulcanian eruption. This eruption provided fragments of the pre-Sept.1st andesite, along with smaller amounts of the essential breadcrust pumices, the glass of which contain 0.4-0.8wt.% of water based on the infrared absorption spectra measurement. Because the cap rock had disappeared, the magma could uplift, upper portion of which effused and made a dome inside the crater. It in turn became a cap rock for the succeeding magma. On Sept. 23rd, next vulcanian eruption took place, the ejecta of this eruption consisting of the lithic fragments and the essential scoria with 0.1wt% water.The textural and chemical analyses of the essential materials ; pumice of Sept.1st and scoria of Sept 23rd, reveal the crystallization process in a chamber-vent system. Following the crystallization of phenocrysts in a deeper magma chamber, two crystallization stages are preserved in crystal size distribution of microlites both in the pumice and scoria. First stage : Magma left the chamber and rose through complex path-steps with ever increasing nucleation. Second stage : In a shallower part in the vent, numerous microlites precipitated rapidly under a high undercooling condition. The similarity between the both CSD patterns implies that their magma had a common ascent history, although groundmass in the scoria has lower crystallinity than that in the pumice, suggesting that the scoria magma stood lower in the magma column.

日本中部的浅间火山在 2004 年 9 月至 12 月期间非常活跃。在其多次喷发中，包括 9 月 1 日的火山喷发和 9 月 1 日的火山喷发。和9月23日。都比较密集。我们将这三周内岩浆的上升和结晶过程描述如下。 9 月 1 日之前，一股新的岩浆柱上升到火山口底部现有的安山岩体中。 9月1日，累积的气压超过了安山岩体的抗拉强度，导致火山喷发。这次喷发提供了 9 月 1 日之前的安山岩碎片，以及少量的必需面包壳浮石，根据红外吸收光谱测量，其玻璃含有 0.4-0.8wt.% 的水。由于盖层消失，岩浆可以隆起，其上部流出并在火山口内形成圆顶。它反过来又成为后续岩浆的盖岩。 9月23日，发生了下一次火山喷发，这次喷发的喷射物由岩屑碎片和含有0.1wt％水的基本熔渣组成。主要材料的结构和化学分析； 9 月 1 日的浮石和 9 月 23 日的熔渣揭示了室通风系统中的结晶过程。随着斑晶在更深的岩浆室中结晶，浮石和熔渣中的微晶石晶体尺寸分布都保留了两个结晶阶段。第一阶段：岩浆离开熔岩室并通过复杂的路径步骤上升，并不断增加成核。第二阶段：在喷口较浅的部分，在高过冷条件下，大量微晶石迅速沉淀。两种 CSD 模式之间的相似性表明它们的岩浆具有共同的上升历史，尽管火山渣中的基质的结晶度低于浮石中的结晶度，这表明火山渣岩浆在岩浆柱中的位置较低。