Continuous chemical monitoring of volcanic gas in Izu-Oshima volcano, Japan |
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| Authors: | Y Shimoike K Notsu |
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| Abstract: | A new continuous monitoring system has been developed for the measurement of volcanic gas from the steam well located 3 km north from the summit of Izu-Oshima volcano, Japan. After removing the water vapor using three sequential dehydration methods, CO2 and SO2 contents are measured using IR sensors, and O2 and H2 using a zirconia sensor and a semiconductor sensor, respectively. This system has been in operation without any significant trouble for 3 years.The dehydrated volcanic gas from the well consists of a mixture of CO2, O2 and N2. A decreasing trend of the CO2 content was observed from 1995 to 1998 together with a decrease of volcanic activity. Seasonal changes have also been observed in CO2 and O2 contents, CO2 being higher and O2 lower in summer, which suggests larger contribution of magmatic components in summer. While changes in short-term variation in CO2 and O2 are influenced by atmospheric pressure changes; the CO2 content correlates inversely with atmospheric pressure unlike O2 with some hours delay. In contrast, the H2 content increased intermittently up to 1200 ppm one to several hours after a sudden drop in the atmospheric pressure and without any apparent correlation with seasonal changes.This system allows us to study temporal variation in chemical composition of volcanic gas during quiescent periods of volcanic activity of Izu-Oshima volcano, and might help us detect anomalous changes before future eruptive events. |
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| Keywords: | Continuous monitoring Volcanic gas Izu-Oshima volcano |
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