2:45 PM - 3:00 PM
[SVC32-05] Airborne measurements of volcanic gases using a UAV to elucidate equilibrium temperature at Sakurajima volcano
Keywords:volcanic gas, UAV, Apparent Equilibrium Temperature, Hydrogen
Sakurajima volcano is one of the most active volcanoes in Japan. Volcanic gas observations are crucial to evaluate the volcanic activities. Because of the risk of eruption, however, access to the proximity of the crater or fumaroles are limited. To conduct the volcanic gas observations, Cessna was used in previous studies (Shinohara et al. 2020); but this observation could only measure diluted volcanic plume. In this study, we conducted volcanic gas observations using a drone to measure concentrated volcanic gases around the crater rim. Three kinds of observations were made: direct sampling of volcanic gas to a bag, conventional Multi-GAS observation, and hydrogen (H2) measurement using a semi-conductor sensor and a desiccant. In this talk, we would focus on the H2 measurement.
Hydrogen is minor species in volcanic gases but provides crucial clues of redox state and temperature in the gas phase and a parental magma(Gigenbach, 1987; Aiuppa et al. 2011). However, it is challenging to measure H2 with low concentration by means of a gas sensor. A semi-conductor sensor has been used to measure volcanic H2 even this sensor is affected by H2O concentration in the volcanic plume: not only cross-sensitivity but also change in H2 sensitivity depending on the H2O concentration (Shinohara et al. 2011). We present a brand new technique to detect and quantify H2 with low concentration (>0.1 ppm) using a desiccant so as to get rid of the interference of H2O on the H2 semi-conductor sensor. We developed a Little Multi-GAS system (LMG) specialized to measure H2 with the desiccant. The system consists of the H2, SO2, H2S sensors, a hygrometer, the desiccant, a battery and a compact logger. This instrument was designed to estimate Apparent Equilibrium Temperature (AET) (Ohba et al. 1994).
In December 2024, we made an airborne measurement of volcanic plume using the drone with LMG at Sakurajima volcano. The four flights were made in total and SO2, H2S, H2, and H2O were quantified successfully. Observed maximum SO2 concentration were from 4 to 50 ppm for each flight. As a result, two kinds of volcanic gases compositions were found: ones with high H2O/SO2 ratios (AET of 500-600℃) and ones with low H2O/SO2 ratios (AET of 700℃). This suggests that there are multiple fumaroles inside of the crater.
Hydrogen is minor species in volcanic gases but provides crucial clues of redox state and temperature in the gas phase and a parental magma(Gigenbach, 1987; Aiuppa et al. 2011). However, it is challenging to measure H2 with low concentration by means of a gas sensor. A semi-conductor sensor has been used to measure volcanic H2 even this sensor is affected by H2O concentration in the volcanic plume: not only cross-sensitivity but also change in H2 sensitivity depending on the H2O concentration (Shinohara et al. 2011). We present a brand new technique to detect and quantify H2 with low concentration (>0.1 ppm) using a desiccant so as to get rid of the interference of H2O on the H2 semi-conductor sensor. We developed a Little Multi-GAS system (LMG) specialized to measure H2 with the desiccant. The system consists of the H2, SO2, H2S sensors, a hygrometer, the desiccant, a battery and a compact logger. This instrument was designed to estimate Apparent Equilibrium Temperature (AET) (Ohba et al. 1994).
In December 2024, we made an airborne measurement of volcanic plume using the drone with LMG at Sakurajima volcano. The four flights were made in total and SO2, H2S, H2, and H2O were quantified successfully. Observed maximum SO2 concentration were from 4 to 50 ppm for each flight. As a result, two kinds of volcanic gases compositions were found: ones with high H2O/SO2 ratios (AET of 500-600℃) and ones with low H2O/SO2 ratios (AET of 700℃). This suggests that there are multiple fumaroles inside of the crater.