火山活動
火山ガス連続測定装置の作製と伊豆大島火山における観測
1997 年 31 巻 2 号 p. 111-117
詳細
1997 年 31 巻 2 号 p. 111-117
We have developed a new continuous monitoring system for volcanic gas chemistry and set up this system at 3 km north from the summit of Izu-Oshima volcano. For continuous monitoring of dry gas, we use three types of dehydration methods to remove water vapor. CO2 and SO2 contents were measured by IR sensors, O2 by a zirconia sensor and H2 by a semiconductor sensor. Our system has been in operation more than 6 months without significant troubles. The dry volcanic gas is a mixture of CO2 of magmatic origin and air component. Temporal variation in chemical composition of the volcanic gas is related with that in atmospheric pressure. The CO2 content is inversely-correlated and O2 is correlated to atmospheric pressure with 8 hours' delay. In contrast, H2 content increases intermittently up to 1000ppm 1 hour after sudden drop of atmospheric pressure. The N2/O2 ratio is higher than the air ratio (3.8), and changes in a similar manner to CO2. This suggests that a part of N2 is of magmatic origin like CO2.
