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Study of volcanic activity monitoring based on continuous measurement of vdcanic gas chemistry

基于Vdcanic气体化学连续测量的火山活动监测研究

基本信息

批准号：
07454140
负责人：
NOTSU Kenji
金额：
$ 4.86万
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 (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Monitoring of volcanic gas chemistry has been carried out only for ambient air of fumarolic fields. Until now there have been few trial to monitor volcanic (vent) gas directly, because common gas sensors do not work well in acid, wet and hot conditions such as in volcanic gas. Therefore, we have deveroped a new continuous monitoring system for volcanic gas chemistry. After high temperature steam of volcanic gas is cooled and removed completely using three types of dehydration apparatus, the chemical compositions of thus obtained dry gas are monitored continuously using an IR sensor (CO_2 and SO_2), a semiconductor sensor (H_2)and a zirconia sensor (O_2).This system was set up at an artificial fumarole inside the summit caldera of Ozu-Oshima volcano and has been in oparation for more than 2 years. This fumarolic gas is a mixture of CO_2 of magmatic origin and air component, and the mixing ratio changes with time both in long and short time ranges. The CO_2 shows an annual variation with high content in summer and low in winter. Generally decreasing trend of summer peak values in CO_2 may be coincide with the decreasing trend in magmatic activity of Izu-Oshima volcano after big eruptions in 1996. A short-term temporal variation of the gas chemistry is related with that in atmospheric pressure. The CO_2 content is inversely-correlated and O_2 is correlated with atmospheric pressure with 8 hour's delay. In constant, the H2 content increases intermittently up to 1000ppm 1 hour after sudden drop of atmospheric pressure. The differnt behaviors of CO_2 and H_2 suggest differnt origins of each species.

仅对火山气田的环境空气进行了火山气体化学监测。到目前为止，几乎没有直接监测火山（排气）气体的试验，因为普通的气体传感器在酸性，潮湿和高温条件下（如火山气体）不能很好地工作。为此，我们研制了一种新的火山气体化学连续监测系统。在使用三种类型的脱水设备将火山气体的高温蒸汽冷却并完全除去之后，使用IR传感器连续监测由此获得的干燥气体的化学组成（CO_2和SO_2），半导体传感器（H_2）和氧化锆传感器（O_2）。大岛火山已经喷发了两年多了。这种火山气是岩浆成因的CO_2和空气组分的混合物，其混合比例在长、短时间范围内都随时间而变化。CO_2的年变化表现为夏季高、冬季低。夏季CO_2峰值的总体下降趋势可能与1996年伊豆大岛火山大喷发后岩浆活动的下降趋势相一致。气体化学的短期时间变化与大气压力有关。CO_2含量与大气压力呈负相关，O_2与大气压力呈滞后8小时的正相关。在恒定条件下，在大气压突然下降后1小时，H2含量间歇性增加至1000ppm。CO_2和H_2的不同行为表明它们的来源不同。