登別大湯沼火口湖の地球化学的研究

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Two explosion craters, Oyunuma and Jigokudani, were formed by the last activity of the Kuttara volcanism. The present volcanic activity makes Oyunuma a typical craterlake filled with 9×10^4 tons of thermal water enriched in chemical constituents. This crater lake was found to have two layers of thermal water distinctly divided by a boundary surface. The upper layer which is well developed all over the crater lake is 50℃ in temperature and more diluted in chemical concentrations, while the lower layer, falling up to 120℃ and having a value of 1.3 in the specific density, contains much more abundant chemical components such as Na^+ and Cl^- than the former does. The thermal water making the upper layer flows out of the crater at a daily rate of 4000 tons after being stored in the lake for 20 days. Concerning the origin of chemical constituents, it was made clear by two test borings that the cracks in the base rock, Kuttara welded-tuff, are filled with the high-temperature water, the chemical property of which is neutral and saline. This thermal water from underground is transported to the bottom of the crater lake, namely, to the lower layer after being diluted with the fresh water under ground. Much more extended dilution takes place on the surface and makes the upper layer more diluted. Volatile sulfur compounds such as H_2S and SO_2 escape from the neutral saline water and are oxidized in the upper layer to make sulfuric acid. It has been observed that the change in the intensity of the volcanic activity disturbs the above mentioned structure of the crater lake and the increasing activity concentrates the chemical constituents in the neutral saline water from underground.
特定非営利活動法人日本火山学会の論文
1966-04-01

登別大湯沼火口湖の地球化学的研究

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