著者

町田 洋 新井 房夫 百瀬 貢

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.30, no.2, pp.49-70, 1985-07-01

被引用文献数

41

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The Aso-4 pyroclastic flow is one of the largest of late Pleistocene age in Japan covering extensive areas of Kyushu around the Aso caldera and western part of Honshu. We have recently discovered a distal ash which has very similar petrographic and chemical properties to the flow deposits at several localities of Japan, and is assumed to be an airfall part of the Aso-4 unit. The ash, named the Aso-4 ash, is a crystal-vitric fine-grained ash, consisting of rhyodacitic bubble-walled glass shards, and brown hornblende and orthopyroxene (bronzite) as mafic phenocrysts. Its identification is carried out by combined parameters ; refractive index of glass ranges 1.506-1.511, low refractive index of orthopyroxene (γ=1.699-1.701) and relatively high index of hornblende (n_2=1.687-1.688). In addition glass in the ash is characteristically rich in potassium. These properties are similar to those of the Aso-4 pyroclastic flows. It is suggested that the ash is a coignimbrite airfall deposit of fine-grained materials from the upper part of an eruption column formed at the same time as the Aso-4 flow. The ash mantles extensive areas from Kyushu to Hokkaido and is also recognized and identified in several piston cores from the Sea of Japan and the northwest Pacific Ocean. The fallout area of this ash is now known to attain approximately 4×10^6 km^2. It is striking that in the eastern part of Hokkaido, ca. 1700 km distant from the source, the ash with the thickness of 15 cm is well preserved immediately below the Kutcharo pyroclasitc flow deposits II/III. The bulk volume of this ash is estimated to be more than 400 km^3, possibly larger than that of the flow deposits. The stratigraphic position of this ash in standard sequence of South Kanto shows that it occurs after the Obaradai interstade (ca. 80 ka) and before the Misaki interstade (ca. 60 ka). Thus the Aso-4 ash provides a very important datum plane in late Pleistocene sequence in and around Japan.

著者

岡田 肇 横山 勝三

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.27, no.1, pp.67-69, 1982-04-30

著者

小林 武彦

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.26, no.2, 1981-07-01

著者

石原 和弘 小林 哲夫

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.33, no.3, pp.269-271, 1988-10-31

被引用文献数

2

著者

小林 哲夫 早川 由紀夫 荒牧 重雄

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.28, no.2, pp.129-139, 1983-07-01

被引用文献数

6

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大隅降下軽石堆積物は, 約22, 000年前に鹿児島湾最奥部で起こった一連の巨大噴火の最初期のプリニアン噴火の産物である.灰白色の軽石と遊離結晶および少量の石質岩片からなる本堆積物は, 全層にわたってほぼ均質な見かけを呈するが, 多くの場合, 上方に向かって粒径がやや大きくなる逆級化層理を示す.層厚分布図(Fig.3)と3種の粒径分布図(軽石の平均最大粒径・石質岩片の平均最大粒径・堆積物の中央粒径;Figs.5, 6, 7)は, いずれも本堆積物の噴出火口が姶良カルデラの南縁, 現在桜島火山の位置する地点付近にあったことを示している.分布軸は火口からN120°E方向に伸びるが, 分布軸から60 km以上離れた地点にも厚く堆積している.又, 堆積物は分布軸の逆方向すなわち風上側にも20 km以上追跡できる.分布軸上で火口から30 km離れた地点での層厚は10 mに達するが, 40 km地点より遠方は海域のため層厚値は得られない.そのため噴出量の見積もりには多くの困難が伴うが, すでに知られている他のプリニアン軽石堆積物の層厚-面積曲線(Fig.4)にあてはめて計算すると, 総体積98 km^3(総重量7×10^<16>g)が得られ, 本堆積物は支笏-1軽石堆積物(116 km^3)に次ぐ最大規模のプリニアン軽石堆積物であることがわかる.3種の粒径分布図から得られる粒径-面積曲線(Fig.8)は, 噴出速度・噴煙柱の高さ・噴出率などで示される噴火の「強さ」を比較する上で有効である.それにより, 大隅降下軽石噴火の「強さ」はけっして例外的なものではなく, プリニアン噴火の平均あるいはそれをやや上回る程度であったことが判明した.

著者

杉浦 孜 杉崎 隆一 水谷 義彦 日下部 実

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.25, no.4, pp.231-244, 1980-12-01

被引用文献数

2

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Ontake Volcano suddenly began to erupt on its south-western flank near the summit at 05^h20^m on Oct, 28, 1979, forming several new craters and ejecting large amounts of volcanic ash and steam. Up to that time, the volcano had been believed to be dormant, though there were weak geothermal activities at a part of the south-western flank of the volcano, Jigokudani. This paper reports some results obtained by preliminary examination of volcanic ashes, thermal waters and gases collected on and around Ontake Volcano during the early stage of eruptive activity. The volcanic ashes are homogeneous in chemical and mineralogical compositions, and similar in chemical composition to the pre-historic volcanic ashes. The ashes contain pyrite, anhydrite, cristobalite and clay minerals. The sulfur isotopic equilibrium temperature is estimated to be about 400℃ for pyrite-anhydrite pairs in the volcanic ashes. The estimated temperature is apparently too high for the temperature of phreatic explosion. The interpretation of this isotopic data remains unsettled. The thermal waters collected from the boiling pools in craters are enriched in D and 19^<O>. The isotopic enrichment is probably caused by evaporation of water at the surface of boiling pool. The hydrogen and oxygen isotopic data also suggest that spring waters issuing around Ontake Volcano are meteoric in origin. Nigorigo Hot Spring, about 4 km north-west of Ontake Volcano, showed significant increases in the concentrations of major dissolved chemical components soon after the eruption, but since then no significant change in chemical and isotopic composition has been observed

著者

神沼 克伊 桜井 治男 馬場 めぐみ 中田 まゆみ

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.25, no.4, pp.313-314, 1980-12-01

著者

久保寺 章

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.26, no.4, 1981-12-28

著者

中禮 正明 福井 敬一 清野 政明

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.31, no.1, pp.63-64, 1986-04-30

著者

日下部 実 荒牧 重雄 金成 誠一 大隅 多加志

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.32, no.4, 1987-12-28

著者

小林 哲夫

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.27, no.4, pp.277-292, 1982-12-28

被引用文献数

12

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Sakurajima Volcano consists of two main stratovolcanoes, Kitadake and Minamidake, which are composed of pyroclastic rocks and lava flows of pyroxene andesites and dacites. The basement rocks are composed of sedimentary rocks such as shale, sandstone, and acidic tuff, welded tuff, and granitic rocks. Geomorphology, large-scale historic eruptions, and the classification of surface textures of andesitic lava flows are briefly summarized. Volcanic history on the basis of the correlation between tephrochronology and the welded pyroclastic deposits is also presented. Taisho and An-ei lavas extruded at the later stage of the eruptions contain microphenocrysts of olivine. Orthopyroxenes of Bunmei pumice of later stage are rich in En content than those of early stage. These facts suggest that the volcanic products of the large eruptions were derived from zoned magma chambers.

著者

中村 一明

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.17, no.1, 1972-06-01

著者

関谷 慱

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.12, no.2, 1967-08-01

著者

小野 晃司 渡辺 一徳

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.29, no.2, 1984-07-01

著者

荒牧 重雄

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.1, no.1, pp.47-57, 1957-01-15

被引用文献数

3

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The pyroclastic flow is defined as the flow of high-temperature, essential, fragmental materials. This is a synonym of the nuee ardente in the broad sense. Three modes of emplacement of high-temperature, essential, solid (or liquid) materials after the ejection from the crater may be recongized: 1) Projection of the fragments from the crater by the explosive expansion of gas which occurs within the crater. 2) Descent of the fragments or liquid magma from the crater which is caused only by the action of gravity. 3) Swift downflow of the mixture of gas and fragments. This is intermediate between 1) and 2) and to this corresponds the pyroclastic flow. A new classification of the pyroclastic flows is proposed. The principle is based upon the viscosity of the materials, which is inferred from the nature of the deposit. The volume of the deposit increases as the viscosity decreases. 1) Nuee ardente in the strict sense. Represented by the nuees ardentes of Mt. Pelee, Merapi, etc. The fragments are less porous, which indicates the high viscosity. The volume of the deposit is small, generally less than 0.01km^3. 2) Pyroclastic flow of the intermediate type. Represented by certain pyroclastic flows of Asama. Hakone. Myoko Volcanoes. The viscosity and volume (0.1〜1km^3) are both intermediate between 1) and 3). 3) Pumice flow. Represented by pumice and tuff flows of all sizes, such as those of Crater Lake, Hakone, Katmai. Aso Volcanoes. Low viscosity leads to the full vesiculation into pumice. Many of them are larger in volume (>10km^3) than 1) and 2), and the caldera of Krakatau type is often formed after the eruption of larger pumice flows.

著者

杉崎 隆一 杉浦 孜 水谷 義彦 日下部 実

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.25, no.2, pp.107-108, 1980-07-01

著者

佐藤 博明

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.30, pp.S173-S188, 1986-03-31

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Recent progress of the study of volcanoes in oceanic areas is reviewed. Major advance of the study has been brought about through the development of the following lines of researches; (1) narrow-beam echo sounding investigation with the aid of precise navigation systems to determine detailed sea bottom topography. (2) deep sea drilling for the determination of stratigraphy of oceanic basement. (3) direct observation and sampling of oceanic basement by submersibles. (4) development of isotope systematics such as Sr-Nd-Pb and He-Ar. (5) increase of accuracy as well as production rate of routine analyses of volcanic rocks; i.e. petrography, mineralogy, major and trace element compositions. Precise high-pressure phase equilibrium studies also afforded important constraints on the modelling of magma genesis in oceanic areas. Geological, petrological and geochemical characteristics of the volcanoes in oceanic areas are described according to the following classification scheme; [A] Monogenetic volcano (a) Oceanic ridge volcano, (b) Back-arc basin volcano, [B] Polygenetic volcano (c) Seamount near oceanic ridge, (d) Seamount near spreading center of back-arc basin, (e) Hot spot seamount, (f) Abyssal plateau, (g) Oceanic island arc volcano. Genetic models of these volcanoes are discussed, and it is shown that the mantle diapir model of SAKUYAMA (1983) can be applied to polygenetic volcanoes in oceanic areas. Generation and uprise of mantle diapir (or blob), and intrusion of mantle diapir into lithosphere may determine the essential features of polygenetic volcanoes; i.e. volume, duration of activity, evolutional history, major and trace element compositions, and isotopic ratios.

著者

早川 由紀夫 荒牧 重雄 白尾 元理 小林 哲夫 徳田 安伸 津久井 雅志 加藤 隆 高田 亮 小屋口 剛博 小山 真人 藤井 敏嗣 大島 治 曽屋 龍典 宇都 浩三

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.29, pp.S208-S220, 1984-12-28

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Stratigraphy and thickness distribution of the pyroclastic fall deposits formed during the eruption of Miyakejima volcano on October 3-4, 1983, were studied immediately after the deposition. Of the total mass of 20 million tons erupted, 8.5 million tons were ejected as basaltic scoria to form a complex set of air-fall deposits east of the fissure vents. One million tons of the latter were ejected from the upper fissures as fire-fountain products. The rest was the product of phreatomagmatic explosions which occurred in the lower fissures where ground water chilled the magma to form dense scoria blocks which devastated villages. Explosion craters and a tuff ring were formed along the N-S trending lower fissures. Account of the general distribution of the deposits, nature of the constituents, mutual stratigraphic correlation and correlation with observed sequence are given.

著者

須藤 靖明

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.20, no.1, pp.1-12, 1975-05-01

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The western region of the Aso Caldera is well known to display the considerable activity of earthquakes. Then, the seismic observation was carried out during three months from June to August of 1973. The purpose of this observation was to analyze the nature of earthquakes and to get information on the tectonic structure at the western caldera rim. The 21 hypocenters were located below the western region and the central cone of the Aso Caldera, and the focal mechanism solutions were determined from the P wave first motions. The distribution of epicenters was distinguished into two zones, one was the zone striking from the Tateno Valley to the west and another was the zone striking north to south along the western rim of caldera. These two zones intersect each other at the Tateno Valley where the caldera wall is breached. The hypocentral depths of earthquakes occurring in the former zone were deeper than in the latter zone. The focal mechanism solutions implied that the direction of maximum compressive stress was northwest-southeast for the earthquakes occurring in the former zone, on the other hand, for the earthquakes occurring in the latter zone the direction of maximum compressive stress was northeast-southwest. These appearances were suggesting that these zones were undoubtedly equal to the tectonic lines and that the right lateral strike slip was occurred at each zone.

著者

鎌田 浩毅 宇都 浩三 内海 茂

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.33, no.4, pp.305-320, 1988-12-28

被引用文献数

4

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中部九州,豊肥火山地域中央部の涌蓋(わいた)山地域には,輝石安山岩質の溶岩流の上に角閃石安山岩質の溶岩流と溶岩円頂丘から成る火山群が形成されている.涌蓋山地域は,耶馬渓(やばけい)火砕流の噴出に伴って形成された猪牟田(ししむた)カルデラの南西縁に位置する.涌蓋山地域に分布する火山岩の地質層序をたて,火山岩のK-Ar年代測定を行なった.涌蓋山地域の火山岩はそれぞれ噴出中心の異なる単成火山群の特徴をもち,猪牟田カルデラの後カルデラ火山活動の産物と考えられる.これらの火山活動は,耶馬渓火砕流噴出直後の1Maから0.3Maまで継続したことが判明した.また火山岩の噴出量と噴出岩石の組成変化を検討した結果,火山活動は0.7Ma付近を境とし,1回の噴出量の多い輝石安山岩質の活動から,噴出量の少ない角閃石安山岩質の活動へと変化したことが判明した.このことは猪牟田カルデラ直下のマグマ溜りの温度が時間とともに低下したことを示唆する.涌蓋山地域の火山活動は0.7 Ma 付近を境として総噴出量が減少し,火山体の形態も溶岩台地卓越型から少数の成層火山体を伴った溶岩円頂丘卓越型へと変化した.涌蓋山地域の火山岩の変化は豊肥火山地域全体のテクトニクスの変化を反映すると考えられる.