IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

1A1_1E-O2Room A3

Date/Time: July 21 9:00-9:15

Estimation of carbon dioxide emission from Kuju Volcano, Japan, and its numericalmodeling
Yasuhiro Fujimitsu1 , Norihide Maeda2 , Sachio Ehara3 , Tetsuro Noda3
1

Faculty of Engineering, Kyushu University, Japan, 2 Graduate School of Engineering, Kyushu
University, Japan, 3 Institute for Geothermal Information, Japan
E-mail: fujimitsu@mine.kyushu-u.ac.jp

Kuju Volcano is located in Kyushu and one of the active volcanoes in Japan. In order to infer the mass balance andenergy balance of the hydrothermal system in the Kuju volcanic area, we tried to estimate volcanic CO2 emission
and to construct a numerical model of the hydrothermal system of Kuju Volcano.
We considered four forms of volcanic CO2 emission; from the fumaroles, the bare area around the fumaroles, theflank by the soil gas, and some hot springs at the foot of the volcano. We adopted the value of about 166 t/day fromthe plumes of Kuju Volcano estimated by Ehara et at. (1981). On the other hand, Itoi (1993) shows the distributionof soil gas CO2 concentration in the bare area around the fumaroles. In our previous study (Araragi et al., 2008),
the relationship between soil gas CO2 concentration measured by the Kitagawa Gas Detector Tube System andCO2 flux measured by a CO2 flux meter in Kuju Volcano was found. Therefore, the CO2 concentration values
shown by Itoi (1993) were converted into the CO2 flux values, and about 0.8 t/day of the volcanic CO2 emission
was estimated. We measured soil gas CO2 concentration at 60 points on the flank of the volcano by the Kitagawa
Gas Detector Tube System and collected 15 soil gas samples to conduct the carbon isotope analysis to identify
the origin of the CO2 . As a result, we concluded that the volcanic CO2 emission from the flank was 0 t/day. Andfor the CO2 emission from the hot springs at the foot of the volcano, the hot water discharge rate and the average
CO2 concentration in the carbonated water of the Nagayu Hot Springs area was adopted. Then about 5.0 t/dayof the volcanic CO2 emission from Nagayu Hot Springs was estimated. These results show that the volcanic CO2
emissions by the plumes from the fumaroles and by the carbonated water from a hot springs area are dominant inKuju Volcano.
In order to construct a numerical model of the hydrothermal system of Kuju Volcano, we used a geothermal
simulator STAR Version 9 (Pritchett, 1989) that can treat the components of H2 O and CO2 but has the limitations oftemperature from 0 to 350 deg. C and pressure from 1 to 600 bars. The modeling area has a horizontal extensionof 25 km (E-W) and 15 km (N-S), and a vertical extension from -500 m asl to the ground surface. Finally, weconstructed a numerical model, which explains the heat discharge rate and CO2 emission rate by the plumes fromthe fumaroles and the CO2 emission rate from the Nagayu Hot Springs area, by trial and error. This numericalmodel also indicates that the volcanic CO2 emission is dominated by the gas from the fumaroles and hot waterfrom Nagayu Hot Springs.

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