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Investigation of volcanic ash monitoring system to predict the manner of magma

研究火山灰监测系统以预测岩浆的方式

基本信息

批准号：
09558050
负责人：
WATANABE Koichiro
金额：
$ 7.81万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
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

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09558050/
关键词：
volcanic ash monitoring Unzen Volcano juvenile material vesiculated glass Kuju Volcano manner of magma non-hydrated glass 顕微FTIR 噴火初期現象マグマ物質 SPT 火山ガラス火山灰モニタリング噴火初期現実

项目摘要

Volcanic ash erupted in an initial stage of volcanic activity has possibility to contain juvenile material directly deprived from latent magma. Detailed studies of the extracted juvenile material may provide effective information to predict magma composition and the manner of magma involving timing and scale of eruption if it will occur. Therefore, monitoring system of volcanic ashes may be one of a potential tool to mitigate volcanic disasters. Based on this concept, we have examined a series of volcanic ash samples erupted from Fugen-dake in Unzen volcano during 1990-1991 and from Iwo-yama in Kuju volcano erupted in 1995, located in the central part of Kyushu island in SW Japan.In order to asses the existence of latent magma near the surface, we collected ash samples erupted from November 1990 to April 1991 in Unzen. Under a microscope, we found a small amount of vesiculated volcanic glasses with remarkably low refractive index in ash erupted on February and April, 1991. We predicted that the existence of latent magma in the shallow level on the basis of our observation. To confirm that the vesiculated volcanic glass is juvenile material, the vesiculated glass without impurities were extracted as glass flakes from each polished this sections. These glass flakes were sprited into two aliquots. One is for measurement of untreated refractive index and other is for measurement of refractive index after annealing to dehydrate. The vesiculated volcanic glass in ash indicated almost the same value in these two kinds of refractive index. Thus the non-hydrated vesiculated volcanic glass in ash seems to be from new magma. It means that these glasses are newly produced because these have not experienced hydration after the formation. The detection of essential material at the time processed more than three months of the lava dome appearance suggests that the monitoring of the volcanic ash is effective for prediction of the manner of latent magma and magmatic eruption.

火山活动初始阶段喷发的火山灰可能含有直接从潜在岩浆中分离出来的幼年物质。提取的幼年物质的详细研究可以提供有效的信息来预测岩浆成分和岩浆的方式，包括喷发的时间和规模，如果它会发生。因此，火山灰监测系统可能是减轻火山灾害的潜在工具之一。基于这一概念，我们研究了位于日本西南部九州岛中部的云仙火山1990-1991年的富源岳和1995年的九州岛火山岩尾山喷发的一系列火山灰样品，为了评估近地表潜在岩浆的存在，我们收集了云仙火山1990年11月至1991年4月喷发的火山灰样品。在显微镜下，我们在1991年2月和4月喷发的火山灰中发现了少量具有显著低折射率的气泡状火山玻璃。在此基础上，预测了浅部有潜在岩浆的存在。为了确认泡状火山玻璃是幼年材料，从每个抛光的切片中提取不含杂质的泡状玻璃作为玻璃薄片。将这些玻璃薄片分成两等份。一种是用于测量未处理的折射率，另一种是用于测量退火至退火后的折射率。火山灰中的气孔状火山玻璃在这两种折射率中表现出几乎相同的值。因此，火山灰中未水合的泡状火山玻璃似乎来自新岩浆。这意味着这些玻璃是新生产的，因为它们在形成后没有经历水合作用。在处理时间超过三个月的熔岩圆顶外观的基本材料的检测表明，火山灰的监测是有效的潜在岩浆和岩浆喷发的方式进行预测。