Pathways for escape of magmatic carbon dioxide to soil air at Unzen Volcano, SW Japan.

Abstract

Estimation of the magmatic contribution to soil air at Unzen Volcano, SW Japan, was carried out using carbon isotopes, both (super 14) C and (super 13) C, and a mixing model of isotopic mass balance in order to assess the spatial variation of magmatic influence from the volcano. The advantage of using soil air samples is that a wide range of gas sampling sites can be selected. Magmatic CO (sub 2) contributed mostly in the eastern region from Unzen Volcano. The high magmatic contribution to soil air appeared along the Akamatsudani fault zone located southeast of the volcano. Our observations across the fault also showed remarkable peaks of CO (sub 2) concentration and delta (super 13) C values, suggesting that magmatic fluid comes up along the fracture zone as for the normal fault system of the graben.