ABSTRACT

The analytical results of volcanic gases of Nasudake, Tochigi Prefecture, Japan were given. The average atomic composition of gases of Nasudake, Showashinzan, Satsuma I.vojima and Kilauea were calculated on the basis of the reported data. Variation in the atomic composition was the smallest at Showashinzan, whereas other three volcanoes showed greater fluctuation. This suggests that gases of the three volcanoes other than Showashinzan are subjected to chemical alteration in their way to the earth's surface. The change in equilibrium composition of gases with temperature was calculated based on the average atomic composition of Showashinzan gases, and was compared with the observed result. Agreement between them was fairly well, suggesting that Showashinzan gases are of magmatic origin and in a closed condition.