Trial building and installing an automatic polythionate monitoring system for forecasting eruption at crater lake

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 07554022
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 試験
• Research Field: 地球化学
• Research Institution: The University of Tokyo
• Principal Investigator: TAKANO Bokuichiro The University of Tokyo, Graduate School of Arts and Sciences, Professor, 大学院・総合文化研究科, 教授 (90012426)
• Co-Investigator(Kenkyū-buntansha): KATSUMATA Junichiro CTI Science Systems KK,Engineer, 技師 ; SUZUKI Katsuhiko The University of Tokyo, Graduate School of Arts and Sciences, assistant, 大学院・総合文化研究科, 助手 (70251329)
• Project Period (FY): 1995 – 1996
• Keywords: Crater Lake / Eruption / Forecasting / Polythionate / Continuous Monitoring / Telemeter / Ion Sensor / Kusatsu-Shirane Volcano

Research Abstract

We have built an automatic polythionate monitoring system for forecasting eruptions at active crater lake floor, and installed it at Yugama crater lake in Kusatsu-Shirane Volcano. This system is composed of submerged plastic container and telemetering devices : in the former a controlling computer unit, water-pumping unit, bottles of solutions, and sensing unit for polythionates, pH and temperature are installed, and a car battery ; the latter includes a solar cell for supplying electricity, a wireless data-sending system, and a modem. The plastic container is 500mm in inner diameter, and 990mm in height with cables for sending data and electricity. We used a nitrate ion-selective electrode for sensing polythionates in the lake water which was pumped into and out the container. In order to get a longer life of the electrode, we reduced acidity of the lake water, using a suppressor for chrtomatographic analysis ; this instrument is composed of two compartments which were separated with a cation exchange membrane. The lake water passes through the inner copartment and potassium hydroxide solution flows through the outer one. Thus proton in the lake water is exchanged with potassium ion, resulting in the reduction of acidity of the water. The pH of the water was adusted to the values between 2.5 and 4. Electrode potentials to polythionates were measured every 12 hours when the electrode was washed with 0.1M ammonium nitrate solution and at the same the potentials to the nitrate solution were also measured for calibrating the electrode. The container was held in the lake five meters from the surface and 10m from the lake floor. We have been accumulating data since November 14,1996.