3:45 PM - 4:00 PM
[SVC31-18] Fumarolic activity before and after seismic events in May 2022, Yakedake Volcano, Japan
Keywords:Yakedake, volcanic gas, hydrothermal system
Since the latest phreatic eruption in 1962-1963, Yakedake volcano has remained dormant, but fumarolic activity around the summit area has continued steadily during the past hundred years. Recently, temperature, chemical, and isotopic compositions of fumarolic gases discharged from the summit fumaroles were ascertained for 2013-2017 (Saito et al., 2019). In May 2022, the seismicity became active in the summit area of the volcano. JMA raised Volcanic alert level to 2 and this was the first time the elevated level had been applied to Yakedake since 2011 (Narita et al. 2022). This time, the fumarolic activities around the summit were observed and sampled gas and waters were analyzed in order to evaluate the influence of the seismic activities in May 2022.
Discharge temperatures of the fumaroles at the northern summit were about 106-110°C, about 10°C higher than the last year’s (2021) value. SO2/H2S measured in July 2022 by gas detector tube showed the highest values since 2013. Apparent equilibrium temperature (AET) was estimated to be about 310°C, about 50°C higher than the last year’s value. Concentrations of CO2, He and HCl has increased since 2021. Other fumaroles showed similar characteristics with the northern summit fumaroles. These results indicate that the fumaroles in 2022 became more active than last year. Higher CO2, He and HCl, SO2 values infer increasing deep magmatic degassing and decreasing shallow hydrothermal activities, respectively.
Gas composition was also measured using a multicomponent gas analyzer system (Multi-GAS; Shinohara, 2005), comparing with the values obtained by gas detector tube. Observed values from Multi-GAS were almost coincide with the values from gas detector tube. At Iwatsubodani fumaroles, located at the southwestern flank of the volcano, H2 was detected by Multi-GAS and AET was estimated to be about 410°C. This value of AET is the highest value among the fumaroles at Yakedake, suggesting that high temperature magmatic gas is supplied to southwestern region of the volcano.
Discharge temperatures of the fumaroles at the northern summit were about 106-110°C, about 10°C higher than the last year’s (2021) value. SO2/H2S measured in July 2022 by gas detector tube showed the highest values since 2013. Apparent equilibrium temperature (AET) was estimated to be about 310°C, about 50°C higher than the last year’s value. Concentrations of CO2, He and HCl has increased since 2021. Other fumaroles showed similar characteristics with the northern summit fumaroles. These results indicate that the fumaroles in 2022 became more active than last year. Higher CO2, He and HCl, SO2 values infer increasing deep magmatic degassing and decreasing shallow hydrothermal activities, respectively.
Gas composition was also measured using a multicomponent gas analyzer system (Multi-GAS; Shinohara, 2005), comparing with the values obtained by gas detector tube. Observed values from Multi-GAS were almost coincide with the values from gas detector tube. At Iwatsubodani fumaroles, located at the southwestern flank of the volcano, H2 was detected by Multi-GAS and AET was estimated to be about 410°C. This value of AET is the highest value among the fumaroles at Yakedake, suggesting that high temperature magmatic gas is supplied to southwestern region of the volcano.