箱根大涌谷温泉ガスのラドン, トロン含量の 1960 年以後の変化とその機構

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A sudden decrease in Rn and Tn contents of the hot spring gas from the Bozu-zigoku hot spring pond, Oowakudani, in 1959 was reported by Kamada (1961). He further discussed both the influence of the volcanic earthquakes which happened in the Hakone region at that time and the mechanism of supply of these radioactive components. The Rn and Tn contents of the gas from Bozu-zigoku have been continually measured by the present authors since 1961. A gradual increase in Rn content from 1961 to 1965 and a sudden decrease was observed in 1966, when the earthquakes occurred again. The variations of the main components have not shown any systematic relations to those of Rn and Tn contents. Tn/Rn ratio was almost constant during these years. Rn content of the gases from drilling holes in Oowakuzawa, few hundreds meters apart from Bozu-zigoku, was found to be rather low. These new data enable us to reexamine and to improve the Kamada's theory on the mechanism of Rn feeding to the volcanic gases. Rn and Tn in the gas seem to be brought out from the source near the ground surface. The gradual increase in these radioactive components from 1961 to 1965 can be explained by any one of the following two mechanisms : (1) The enrichment of Ra and Th by the adsorption on clay minerals from the hot spring waters ; or (2) the increase in the contact area, which is effective to feed Rn and Tn to the gas, due to the alteration. The decreases observed in 1959 and 1966 were concerned with repeated shocks of the earthquakes at those times and can be explained by either one of the two mechanism : (1) Closing of the minute cracks where Ra and Th are enriched, the extraction of Rn and Tn to the hot spring gases and waters is hindered ; or (2) the decrease in the contact area of the source with gas and water. An approximate size of the source volume was also estimated.
特定非営利活動法人日本火山学会の論文
1968-04-01

箱根大涌谷温泉ガスのラドン, トロン含量の 1960 年以後の変化とその機構

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