Fischer, T.P.

Ishida, A.

Kagoshima, T.

Lan, T.F.

Nishio, Y.

Pinti, D.L.

Roulleau, E.

Sano, Y.

Takahta, N.

Tomonaga, Y.

Tsunogai, U.

OceanRep

Goldschmidt Conference Abstracts  2729 Spatial and temporal variations of helium and carbon isotopes at Ontake volcano, Japan YUJI SANO1, TAKANORI KAGOSHIMA1, NAOTO TAKAHATA1, AKIZUMI ISHIDA1, YAMA TOMONAGA2, EMILIE ROULLEAU3, DANIELE L. PINTI4, TOBIAS P. FISCHER5, TEFANG LAN6, YOSHIRO NISHIO7 AND URUMU TSUNOGAI8 1Atmopshere and Ocean Research Institute, University of Tokyo, Japan (ysano@aori.u-tokyo.ac.jp),  2Swiss Federal Institute of Aquatic Science and Technology, Switzerland,  3Centro de Excelencia de Geotermia de los Andes, Department of Geology, Universidad de Chile, Chile,  4GEOTOP & Department des sciences de la Terre et de l’atmosphere, Universite du Quebec a Montreal, Canada,  5Department of Earth and Planetary Sciences, University of New Mexico, USA,  6Institute of Earth Sciences, Academia Sinica, Taiwan,  7Reseach and Education Faculty, Kochi University, Japan,  8Graduate School of Environmental Studies, Nagoya University, Japan.  We report spatial and temporal variations of helium and carbon isotopes measured in CO2-rich bubbling gases from natural springs associated with Ontake volcano (central Honshu, Japan) from November 1981 to September 2015. During the whole period, the 3He/4He and CO2/3He ratios decreased with increasing distance of sampling site from the central cone. In contrast, δ13C values of the CO2 increased with the distance. These spatial trends became more significant after the 27 September 2014 Ontake eruption, suggesting the reactivation of the volcano plumbing system with enhanced emission of magmatic volatiles. The 3He/4He ratios of the closest site to the central cone stayed constant until 2000 and increased apparently from June 2003 to October 2014 and became constant soon after the eruption until September 2015. The ten-year helium-3 enhancement may have been a precursor of the 2014 Ontake eruption. In contrast, δ13C values of CO2 at the same site stayed constant all over the period. Lack of δ13C anomaly may be attributable to ; 1) either negligibly small amounts of magmatic CO2 introduced into the source of hot spring compared with ambient CO2 in the aquifer; 2) or that the carbon signature of magmatic CO2 is very similar to that of ambient CO2 and thus its addition cannot change the overall δ13C value of the sampled hot springs. At the distant sampling sites no valuable changes of helium and carbon isotopes were observed in relation to the 2014 Ontake eruption, suggesting that the impact of this eruption on the Ontake hydrothermal system was geographically localized.  

Spatial and temporal variations of helium and carbon isotopes at Ontake volcano, Japan

http://oceanrep.geomar.de/43242/1/2729.pdf

Spatial and temporal variations of helium and carbon isotopes at Ontake volcano, Japan

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