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タイトル: Geological Investigations on the Zao Volcanoes : I. Goshiki-dake, a Central Cone of the Zao Proper.
その他のタイトル: 藏王火山の地質學的研究(第1報)
著者: 市村, 毅
著者(別言語): ICHIMURA, Takeshi
発行日: 1951年8月30日
出版者: 東京大学地震研究所
掲載誌情報: 東京大學地震研究所彙報. 第29冊第2号, 1951.8.30, pp. 327-339
抄録: (i) Goshiki-dake is a central cone of the Zao proper and rises up to 1674 meter above the sea level. It is formed within the semi-circular explosion crater surrounded by Kumano-dake, Umanose, Katta-dake and Haizuka-yama. (ii) This central cone rests upon the eroded surface of lava flows and ejecta which have their sources in the pre-existing crater destroyed largely by later explosions, being deeply dissected and highly cliffed along the Osawa and at the eastern side of Okama. It has a diameter of more than 1000 meters at its base and is about 200 meters high above the bottom of the Osawa. (iii) The central cone is chracterized by the presence of explosion cratercalled generally "Okama" which is found at dts western side. It is a nearly circular depression about 300 meters in diameter, being now filled with beautifully-colored water. (iv) The internal structure is well shown along the crater wall and high cliff dissected deeply by the Osawa. The cone is built up of ash, sand, lapilli and agglomerate which are distinctly stratified and incline to the west at an angle of 10°-15°. They have accumulated alternately with no intercalation of lava flows. The surface of the central cone and its surrounding area are largely veiled with recent ejecta thrown out from Okama. They are composed of ash and lapilli, the prevailing color being light grey or grey. (V) Volcanic sand and ash here consist of plagioclase, augite, hypersthene and magnetite as well as of tuffaceous substances and minute fragments of two pyroxene andesite. The recent lapilli is, however, represented by two pyroxene andesite subjected mostly to solfataric action. Agglomerate contains angular or subangular fragments of two pyroxene andesite with such component minerals as labradorite, bytownite, augite, hypersthene, magnetite and brown glass. (vi) The volcanic activities of the central cone are recorded since 884. The most recent one took place in 1939. So far as is shown by historic records, these activities always took place in Okama, and the explosion was frequently followed by the inundation of lake water which caused a serious damage to the district along the Nigori-gawa, Matsu-kawa, Shiroishi-gawa, etc. The fumaroles newly opened in 1940 are still active at present, their exhalation being composed mainly of superheated steam with a small amount of SO2. In conclusion, the writer's thanks are due to Dr. H. Tsuya who allowed him to continue his work in the Earthquake Research Institute of Tokyo University. The writer is also deeply indebted to Mr. R. Morimoto and Mr. F. Hori for their co-operation in his laboratory work. The expense of this research was defrayed from the fund for the Scientific Research of the Educational Ministry.
URI: http://hdl.handle.net/2261/11678
ISSN: 00408972
出現カテゴリ:東京大学地震研究所彙報
東京大学地震研究所彙報

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