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久六島西方海底の熱水活動 Hydrothermal Activity on the Sea Floor, West of Kyuroku-sima Island, Japan Sea 福留, 高明 山科, 健一郎 FUKUDOME, Taka-aki YAMASHINA, Ken'ichiro Hydrothermal activity was discovered at the bank to the west of Kyuroku-sima Island which is considered to have subsided by about 30-40 cm associated with the 1983 Japan Sea earthquake. This area is covered with yellowish brown deposits (travertine). The deposits are essentially composed of Fe-oxide (or -hydroxide), amorphous SiO_2 and clay minerals, and contain a high content (600 ppm) of As as a trace element. Degassing of small quantities of unknown gas has been observed and shellfishes such as turbos have been suffered death in this area. The sea water near the degassing spots is richer in Si and shows lower pH value than the normal sea water. This indicates that the hydrothermal activity continues up to the present. There is a possibility that the hydrothermal phenomena are ascribed to the volcanism in a relatively young age (Quaternary?). No Quaternary volcano has hitherto been known in this area and its vicinity. However，new facts obtained as results of our investigation seem to intimate the existence of it. 秋田大学鉱山学部 1985-10-22 jpn departmental bulletin paper VoR http://hdl.handle.net/10295/2195 https://air.repo.nii.ac.jp/records/2047 03898040 AN00010307 秋田大学鉱山学部研究報告 6 151 157 https://air.repo.nii.ac.jp/record/2047/files/fukudome4.pdf application/pdf 11.2 MB 2017-02-16