著者

宮縁 育夫 増田 直朗 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 (ISSN:04534360)

巻号頁・発行日

vol.49, no.5, pp.267-282, 2004

参考文献数

31

被引用文献数

7

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The western part of post-caldera central cones of Aso Volcano, southwestern Japan, is characterized by wide chemical variation of lava flows (SiO₂=49-73 wt.%) and complicated topography. Geologic history of the area was reconstructed by stratigraphic relationships between lava flows and airfall tephra layers. Stratigraphy and chronology of lavas and tephra distributed on the western slope of the central cones are as follows: Ayugaerinotaki lava, Matsuhata pumice (MhP), Tochinoki lava (73±10 ka; K-Ar age), Aso central cone pumice 4 (ACP4), Tateno lava. Aso central cone pumice 3 (ACP3), Takanoobane lava (51±5ka), Eboshidake lava, Karisako lava, Akase lava (30 cal ka ; calibrated ¹⁴C age), Sawatsuno lava (27±6ka), Kusasenrigahama pumice (Kpfa; 31 cal ka), Otogase lava and Aso central cone pumice 1 (ACPI ; 4 cal ka), in ascending order. Between about 70,000 to 50,000 years ago Tochinoki lava, Tateno lava and Takanoobane lava accompanied precursor pumice-fall deposits. A catastrophic eruption occurred in and around the Kusasenrigahama crater at 31 cal ka. The eruption was initiated by the dacite Sawatsuno lava now and produced the largest plinian numice-fall deposit (Kpfa; 1.2 km³ in DRE volume). In the western part of post-caldera central cones of Aso Volcano, total discharge volumes of felsic and mafic magmas from about 70,000 to 30,000 years ago were estimated to be about 2.4 km³ and 0.47km³ respectively.

著者

小野 晃司 渡辺 一徳 星住 英夫 高田 英樹 池辺 伸一郎

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.40, no.3, pp.133-151, 1995

参考文献数

41

被引用文献数

21

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We describe in this paper the character of ash eruption of Nakadake volcano presently going on and maintain that the products of the volcano during the recent geologic past are the main constituents of ashy soils distributed around, especially to the east of, the volcano. Nakadake volcano, the only active central cone of Aso caldera, mainly discharges black, sandy essential ash of basaltic andesite during its active period. The ash is the most voluminous constituent of the products of Nakadake through its activity of recent more than 20,000 years. We call ash eruption for the activity which discharges dominantly ash. The ash is divided into three groups : block-type ash, splash-type ash, and free crystals. The block-type ash, most common, is polyhedral surrounded by a few flat planes. It is formed by brittle fracturing of semi-solid top part of the magma column. While, the splash-type ash, discharged only during the very active phase in active periods, is derived from liquid magma which underlies the semi-solid top of the column. The ash is transported by gas stream from the magma in a quasi-steady state or intermittently, and is distributed around Nakadake volcano in a near-circular pattern by a low eruption column usually less than 1,000 m in height. Long-term thickness contours of the ashy soil from Nakadake volcano in three time intervals, separated by the present earth surface and three ash or pumice layers, of recent more than 20,000 years also show near-circular pattern but a little elongated to the east. 'Loam beds', mainly composed of decomposed and argillized volcanic ash, are said to be formed by accumulation of aeolian dusts during periods of no eruption in volcanic districts. But, loam beds (Akaboku) and black humic soils (Kuroboku) distributed around Aso volcano are composed mainly of primary fall-out deposits of ash or pumice along with aeolian dusts. Ash eruption of Nakadake mostly produces sandy ash rather continuously without long time break but in small rate of discharge. A correlation of detailed columnar sections eastwards of Nakadake crater shows most single strata of ashy soils, light brown- to black-colored, thin according to the increase of distance from the source crater. The ash, especially very fine ash distributed in the distal area, easily decompose and lose primary stratification to form a massive layer which is hardly discernible from aeolian loam beds by their close resemblance. Not only fine ash layers but Plinian pumice fall layers form 'loam' beds which are not distinguishable with adjacent aeolian beds by further decomposition. The thickness contours of the Kanto loam elongate and thin eastward from Fuji volcano over the Kanto plain. The thickness of loam beds changes regionally, thicker in volcanic areas and thinner in non-volcanic areas. These facts suggest contributions of primary pyroclastic falls for thickening of 'loam beds'

著者

星住 英夫 渡辺 一徳 阪口 圭一 宇都 浩三 小野 晃司 中村 武

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 (ISSN:24335320)

巻号頁・発行日

vol.1997, 1997

著者

小野 晃司 渡辺 一徳 星住 英夫

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.40, no.3, pp.212-213, 1995-07-31

著者

渡辺 一徳 勝井 義雄

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.71, no.2, pp.44-49, 1976-02-05 (Released:2008-08-07)

参考文献数

16

被引用文献数

28 30

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阿蘇カルデラ内北部の本塚・北塚・灰塚はいずれも石英安山岩の溶岩からなる古い中央火口丘で,それらの下底部には海抜約510mのレベルまで水冷により破砕された溶岩が発達している。故にこの水中溶岩が噴出した時期にはカルデラはこのレベルまで湖であったと推定される。この水中溶岩は大小の岩塊と同質の細片からなり,その中には枕状溶岩に類似した柱状節理をもつ岩塊が含まれている。この種の岩塊は多くの点で通常の枕状溶岩とは異なっているので,偽枕状溶岩と呼ぶことにする。その産状の詳細な観察によれば,偽枕状溶岩は,水中を前進中の粘性の高い溶岩に湾曲した割れ目がはいり,これに沿って侵入した水で急冷され,分離したものである。このため偽枕状溶岩は表面に垂直な柱状節理を生じているが,通常の枕状溶岩とちがって外形はもとの流理構造を明瞭に切っている。

著者

宮縁 育夫 星住 英夫 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 (ISSN:04534360)

巻号頁・発行日

vol.49, no.2, pp.51-64, 2004-05-20 (Released:2017-03-20)

参考文献数

33

被引用文献数

5

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The stratigraphy and chronology of late-Pleistocene (after deposition of AT ash) tephra layers erupted from post-caldera central cones of Aso Volcano, SW Japan, are evaluated through study of the thick tephra sequence preserved mainly atop the pyroclastic-flow plateau east of the caldera. Twenty andesite to basaltic-andesite scoria-fall deposits (YmS20-YmS1 in ascending order) and two pumice-fall deposits (NbP2 and NbP1) were identified as maker beds for the interval ca. 29-13ka (calibrated 14C age). The tephra layers were produced mostly by scoria and ash eruptions of Nakadake, the only active post-caldera central cone, and their bulk volumes calculated from isopach maps range from 0.01 to 0.9km3. The radiocarbon ages of buried soils just below individual tephra layers reveal that YmS20 to YmS15 were erupted at ca. 22-21 ka and YmS20 to Ym-S1 at ca. 18-16ka. Total tephra volume during 29-13ka is estimated at about 1.3km3 (DRE). Production of tephra was mainly concentrated in two periods : 22-21 ka (0.8km3) and 18-16ka (0.5km3).

著者

宮縁 育夫 増田 直朗 渡辺 一徳

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.43, no.5, pp.353-358, 2004-10-01 (Released:2009-08-21)

参考文献数

23

被引用文献数

4 4

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阿蘇カルデラ西部に分布する立野溶岩の直下に,軽石層が存在することが認められ,その軽石層は阿蘇中央火口丘第4軽石(ACP4)に対比された.また,ACP4直下から未炭化の樹木根を採取し,加速器質量分析法による14C年代測定を行った.得られた年代は>43,200 14C yrs BP(>約46cal kaに相当)であり,立野溶岩の上位に存在する高野尾羽根溶岩のK-Ar年代(51±5ka)とも矛盾しない.阿蘇火山中央火口丘群の西部地域では,50ka前後に数100年程度の時間をおいて,立野溶岩と高野尾羽根溶岩というデイサイト~流紋岩質溶岩の流出が2回あり,それらの直前にはプリニー式噴火が発生し,多量の降下軽石が放出されていることが明らかになった.

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

渡辺 一徳 本田 圭一 原 浩太郎 宮縁 育夫

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.66, no.1, pp.21-34, 2021-03-31 (Released:2021-03-25)

参考文献数

36

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Aso Volcano in central Kyushu, SW Japan, is one of the largest caldera volcanoes in the world. Aso caldera, 25 km north-south and 18 km east-west, was formed by four gigantic ignimbrite eruptions: Aso-1 (270 ka), Aso-2 (140 ka), Aso-3 (120 ka) and Aso-4 (90 ka). The only outlet of the caldera, named as Tateno gorge, is located at the western edge of the caldera. Since the gorge’s formation history remains poorly studied, a detailed geologic study has been conducted to clarify the stratigraphic relationships between lavas and Aso ignimbrites, and evaluate the formation age of the gorge. The gorge walls are composed mainly of pre-Aso volcanic rocks (0.8-0.4 Ma), and densely welded Aso-2 pyroclastic flow deposits occur on both northern and southern walls of the gorge. Andesitic lava flows (Hokamaki lava) are found between the Aso-1 and Aso-2 ignimbrites in the gorge, and the lavas show potassium-rich characteristics that are indicative of the whole-rock chemistry of magmatic products from Aso Volcano. Additionally, welded Aso-1 blocks were observed in the gravel beds (lahar deposits) underlying the Hokamaki lava from borehole cores. The evidences suggest that the origin of Tateno gorge, which was draining a pre-existing caldera, formed after the Aso-1 ignimbrite eruption (270 ka), and thereafter Hokamaki lavas and the Aso-2 pyroclastic flows (140 ka) passed through the gorge.

著者

宮縁 育夫 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 (ISSN:04534360)

巻号頁・発行日

vol.45, no.1, pp.25-32, 2000-03-10

被引用文献数

3

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Jigoku spa is located west of Ikenokubo basin of Yomineyama volcano, southwestern part of the central cones of Aso volcano. In this basin, "Ikenokubo tuff ring" and two smaller maars were developed. Two layers of ejecta, about 10^5 m^3 in bulk volume, formed by phreatic explosions were found in this area. They are very poorly sorted and mainly composed of altered fine-grained ash including lithic fragments. Kikai Akahoya ash erupted about 6,300 years BP (^<14>C) is intercalated between two layers of phreatic ejecta in thick ash layers from Nakadake, the only active central cone. Based on ^<14>C ages of buried Andisols and the succession of the deposits, the eruption ages of the two ejecta are estimated at about 10,000 years BP for older deposit and at about 4,500 years BP for younger one. Distributions of thickness and maximum grain size of the lithic fragments suggest that the both of two phreatic ejecta were exploded not from "Ikenokubo tuff ring" and two maars but from the Jigoku explosion crater in the western area. Ejecta correlative to the "Ikenokubo tuff ring" Iies under the older of the phreatic ejecta layers. Consequently, the eruption age of "Ikenokubo tuff ring" is probably older than 10,000 years BP. Frequency of phreatic explosions, Iarger than 10^5 m^3 in volume, is considered to be once in about 5,000 years. This fact is noteworthy for volcanic hazards assessment in the surrounding area of Jigoku spa and adjacent Tarutama spa.

著者

石坂 信也 渡辺 一徳 高田 英樹

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.31, no.2, pp.91-99, 1992-05-30 (Released:2009-08-21)

参考文献数

25

被引用文献数

3

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熊本平野とその周辺には多くの活断層が存在することが知られている. 筆者らは, 熊本平野やその周辺に掘られた多数のボーリングの中で重要なもの50本余りのコアを, 改めて詳細に観察した. ボーリングコアには, 約6,300年前に鬼界カルデラから噴出したアカホヤ火山灰, 約30万年前以降に阿蘇カルデラから噴出したAso-1~Aso-4火砕流堆積物などの重要な鍵層が認められる. それらの放射年代と深度の差異から, 熊本平野における最近の約15万年前以降の第四紀層の沈降速度を見積もることができた. 平野南部での平均沈降速度はおよそ0.2~0.5mm/年であり, そこは, 熊本平野の周辺で確認されていた活断層による木山-嘉島地溝 (渡辺ほか, 1979) およびその西方延長部にあたる. 平野西部での沈降速度はおよそ0.2~0.3mm/年である. これらの沈降は, 熊本平野地下の活断層の動きによって引き起こされていると考えられる.

著者

渡辺 一徳 小野 晃司

出版者

日本地質学会

雑誌

地質學雜誌 (ISSN:00167630)

巻号頁・発行日

vol.75, no.7, pp.365-374, 1969-07-25

被引用文献数

6 12 5

著者

宮縁 育夫 星住 英夫 高田 英樹 渡辺 一徳 徐 勝

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.48, no.2, pp.195-214, 2003-05-20

被引用文献数

12

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Aso central cones located within Aso caldera, central Kyushu, southwestern Japan, initiated their activity soon after the formation of the caldera (ca. 90 ka). The cones have produced voluminous airfall tephra layers and lava flows. Most of the tephra layers distributed in and around Aso caldera are andesite to basaltic-andesite scoria-fall and ash-fall deposits. Their stratigraphy is very complicated because it is difficult to distinguish between scoria-fall layers in the field. However, dacite to rhyolite pumice-fall deposits from some central cones interbedded between the tephra layers are very useful to correlate stratigraphic units at separated localities. Therefore, we used the pumice-fall deposits in order to construct the tephrostratigraphy and eruptive history of Aso central cones during the past 90,000 years. Thirty-six pumice-fall deposits were identified including eleven major key beds. In ascending order they are Nojiri pumice (NjP), Ogashiwa pumice (OgP), Yamasaki pumice 5 (YmP5), Sasakura pumice 2 (SsP2) and 1 (SsP1), Aso central cone pumice 6 to 3 (ACP6-ACP3), Kusasenrigahama pumice (Kpfa) and Aso central cone pumice 1 (ACP1). Phenocrystic minerals of most pumice are plagioclase, ortho- and clino- pyroxene and magnetite, but NjP, ACP5, ACP3 and ACP1 include biotite, and NjP and SsP2 contains hornblende phenocrysts. On the basis of several ^<14>C ages of buried soils just below pumice (above Kpfa) and stratigraphic position eruption ages for the eleven major pumice are estimated as follows: NjP (85 ka), OgP (80 ka), YmP5 (69 ka), SsP2 (57 ka), SsP1 (56 ka), ACP6 (52 ka), ACP5 (45 ka), ACP4 (40 ka), ACP3 (39 ka), Kpfa (31 ka) and ACP1 (4ka). During the past 90,000 years Aso central cones produced pumice-fall deposits at an interval of about 2,500 years. Many of the sources of the pumice appear now buried under the present Aso central cones.

著者

渡辺 一徳 高田 英樹 岡部 良子 西田 晃代

出版者

熊本大学

雑誌

熊本大学教育学部紀要. 自然科学 (ISSN:04546148)

巻号頁・発行日

vol.44, pp.15-22, 1995-12-15

著者

宮縁 育夫 池辺 伸一郎 渡辺 一徳

出版者

特定非営利活動法人日本火山学会

雑誌

日本火山学会講演予稿集

巻号頁・発行日

vol.2005, 2005-10-05

著者

田村 実 スタンレー ジョージ・デ STANLEY George D.Jr. ジェームズダブルシアーズ 渡辺 一徳 ジョージ・ディー・スタン

出版者

熊本大学

雑誌

国際学術研究

巻号頁・発行日

1992

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研究成果報告書日本の三宝山帯とはアルプス等テチス海域に特徴的なメガロドン石灰岩をはじめとする二枚貝及び造礁性サンゴ化石が報告されている。日本はアルプスを含むテチスプロパ-地域とテチスフォーナを含む米国太平洋岸地域の中間的位置を示している。勿論日本及び北米のテチスフォーナを産する地域はExotic terranesではあるが,テチス域の当時の古地理をしらべる上で重要な資料を提供しうるという点でこの度の共同研究となった。1993年に田村はWallowa産地を訪れ,又スタンレーは1993年9月より1994年8月はじめまで日本に滞在し,球磨川流域,熊本県の八代郡水上越,奈良県のアザミ谷,沖縄の今帰仁層の資料に基き,専門は異なるが夫々の資料を提供し,日本とアメリカの三畳紀(特に後期三畳紀)テチス化石群の対比を二枚貝とサンゴに基づいて行い,更にテチス域全体についてにも対比を広めた。現在入手しうる最大の資料(化石)を用いて検討したが資料の不足はなお残る。特に日本のサンゴ化石は保存が悪く又産出は礫からに限られているため充分な研究ができたとはいいがたい。今後更に資料の蓄積に努力してより確度の高い結果をえたい。全体的な結論として二枚貝・サンゴ共,テチス要素を含みテチスフォーナに属するが夫々がEndemicな要素の含有率が高く,又日米双方間についても二枚貝では共通種がなく,サンゴでは北米産60種のうち1種が共通するだけで,分布を容易にする環境ではなかったと考えられる。以下に研究により判明したことを箇条書に示す。二枚貝の研究(1)ニュートン他は北米ワラワ山地の二枚貝化石群をテチス域のものとしたが,この中に日本ではテチス域(三宝山帯)に全く産せずより内側の河内ケ谷フォーナの要素の産出を報じたが検討の結果ワラワ山地で河内ヶ谷フォーナの種に同定又は類似種とされたもののいづれもが異なることが以下の如く明かになった。(2)テチスフォーナ中の三角貝類を検討した結果,次のことが明らかになった。a.日本産の上部三畳系の三角貝はGruenewaldia decussata,Gruenewaldia vokhlmanni,Kyushutrigonia hachibarensis new genss and next species,Prorotrigonia(?)sp.でこれらはテチス域から中国西部にかけての

著者

宮縁 育夫 池辺 伸一郎 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 (ISSN:04534360)

巻号頁・発行日

vol.50, no.4, pp.227-241, 2005-08-31

被引用文献数

6

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Ash emissions occurred from a hot water pool of one of the craters of Nakadake, the only active central cone of Aso Volcano, southwestern Japan, on July 10, 2003 and January 14, 2004. The former ash was dispersed throughout an area extending 14km east-northeast of the vent, whereas the latter ash extended 8km to the east-southeast. Based on isopleth maps, the total weight of ash discharged by each event was 41tons and 32tons, respectively. Both ash-fall deposits were composed of fine-grained (<1mm) glass shards, crystals and lithic fragments, and contained neither lapilli nor blocks. Some glass shards appear fresh and are probably juvenile material. We therefore believe that these phenomena represent non-explosive gas-and-ash emissions through the hot water pool. The ash particles emitted from the hot water pool of the Nakadake crater were aggregated at a size of 1-3mm and deposited because of a high content of water. The ash-fall deposits in proximal areas (<1.5km from the crater) were finer grained and more poorly sorted than in distal areas (>5km). Moreover, the deposit volume obtained from actual data in the proximal area was much larger than the volume extrapolated only from the isopleth data of the distal deposits. These phenomena suggest that the proximal deposits were emplaced mainly by another fine-grain-rich column different from the main ash plume that extended to distal areas, or that some parts of the column detached from the main plume that emplaced the proximal deposits.

著者

宇井 忠英 隅田 まり 大学合同観測班地質班 荒牧 重雄 大島 治 鎌田 桂子 小林 武彦 小屋口 剛博 佐藤 博明 中川 光弘 中田 節也 藤井 敏嗣 藤縄 明彦 古山 勝彦 三宅 康幸 横瀬 久芳 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 (ISSN:04534360)

巻号頁・発行日

vol.38, no.2, pp.45-52, 1993-07-01

被引用文献数

2

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Small-scale pyroclastic flows due to the collapse of the lava dome have been frequently generated during the 1991-93 eruption of Unzen Volcano. We have recorded video footages which show the generation of pyroclastic flows during January-March 1992. Two types of phenomena have been observed : deformation of the lava dome due to flowage ; and a sudden discharge of gas and ash through fractures and peeling-off of rock fragments from the surface of cooling lava blocks. Pyroclastic flows were generated only in places on the lava dome where these precursory phenomena were frequently observed.