1965 Volume 38 Issue 11 Pages 1946-1954
Continuous observations of fumarolic gases have been made in order to study the chemical nature of volcanic gases. A very wide variation in the content of some gaseous constituents has been observed in continuous observation over several hours, and over four years.
Judging from the field observation and the mode of the content variation of several components with the time and the temperature, it is likely that process of the alteration of volcanic gases occurring in the sub-surface plays an important role in producing the difference in the chemical nature of fumarolic gases among the fumarole areas. In addition, the year-to-year variation of the contents of some constituents might provide an indication of the stage of some processes, such as distillation and occlusion, which have occurred in the sub-surface.
It has been found that components like selenium are useful in an examination of the behavior of volcanic gases at an old solfataric volcano like Nasudake, because it is expected that most of the constituents except for selenium have been accumulated in the sub-surface by the past effusion processes and that the accumulated constituents have been occluded in the primary volcanic gases with the change in volcanic activity.
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