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.

日本中部的阿萨马火山在2004年9月至12月活跃。在其几次爆发中，9月1日的瓦坎尼亚爆发。和9月23日。相对密集。我们描述了岩浆在这三个星期中的上升和结晶过程，如下所示。 9月1日之前，一列新的岩浆已进入火山口地板下面的预处理体。 9月1日，堆积的气压超过了安山岩体的拉伸强度，导致瓦肯尼爆发。这次喷发提供了九个安山岩的碎片，以及较小量的必需面包屑浮石，基于红外吸收光谱测量，其玻璃含有0.4-0.8wt。的水。由于帽子岩石已经消失，岩浆可以提升，上部有其上部，并在火山口内制成一个圆顶。反过来，它成为后续岩浆的帽子岩石。 9月23日，下一次瓦坎尼亚爆发发生了，这种喷发的射出由岩性碎片和基本的Scoria组成，并带有0.1 wt％的水。必需材料的纹理和化学分析； 9月1日和9月23日的Scoria的浮华揭示了腔室通风系统中的结晶过程。在较深的岩浆腔中的表晶结晶之后，在浮石和斯科里亚中的微果石的晶体尺寸分布中保留了两个结晶阶段。第一阶段：岩浆离开腔室，穿过复杂的路径步骤，成核的增加。第二阶段：在通风口的较浅部分中，许多微层在高底冷条件下迅速沉淀。两种CSD模式之间的相似性都意味着它们的岩浆具有共同的上升历史，尽管Scoria中的地面质量的结晶度低于浮石，这表明Scoria Magma在Magma柱中较低。