著者

菅 香世子 小林 勝己 印牧 もとこ 宮原 智哉 遠藤 邦彦

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.37, no.2, pp.71-83, 1992

参考文献数

21

被引用文献数

4

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Kozushima consists of rhyolitic monogenetic volcanoes (lava domes and thick lava flows), and is located on Zenisu Ridge, northern part of Izu-Bonin Arc. Activities of the momogenetic volcanoes were accompanied with pyroclastic flows and surges. But their succession and stratigraphy are not well known. We tried to discuss them based on observation in construction field of Kozushima Airport and its neighborhood in southern part of the island. Three pyroclastic surge deposits were confirmed on thick lava flow which was fomed tens of thousands years ago. They are, Chichibuyama pyroclastic-surge deposit-B which was older than 22,000 y.B.P., Chichibuyama pyroclaslic-surge deposit-A which erupted 21,000-19,000y.B.P. and Tenjosan pyroclastic-surge deposit which was fomed 838 A.D. in ascending order. Two regional ash-fall deposits which originated from gigantic eruptions in Southern Kyushu and several ash-fall deposits from another islands were interbeded with them. Thus, only three pyroclastic surge deposits have come to deposit in southern part of Kozushima while tens of thousands years. It does not mean that only three eruptions occurred in Kozushima the while, but suggests that most eruptions could not bring pyroclasic materials on the thick lava flow whose height is 100-300 m in southern part of Kozushima except above mentioned three eruptions. Most pyroclastic flows and surges were strongly controled by topography in Kozushima, but some were not. That might be caused by the difference of eruption energy or eruption types.

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

早川 由紀夫

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.Special, pp.S1-S15, 1995-12-25 (Released:2017-03-20)

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Age of a tephra can be determined by simple stratigraphy, if adequate number of time-markers are provided. Eleven master tephras are chosen as the time-markers for the last one million years. They are Kikai-Akahoya (7.330 ka), Aira-Tanzawa (26.00 ka), Daisen-Kurayoshi (50.00 ka), Aso-4 (87.00 ka), Ata-Torihama (250.0 ka), Kakuto (340.0 ka), Suiendani-TE5 (420.0 ka), Kobayashi-Sakura (540.0 ka), Kaisyo-Toriitoge (650.0 ka), Shishimuta-Azuki (870.0 ka), and Shishimuta-Pink (1000 ka). The present earth surface and Bruhnes/Matuyama boundary (780.0 ka) play a same role as master tephras. Ages of some master tephras are assigned rather arbitrarily, however, it is productive to affix them once to a specific value. A tephra sandwiched between two master tephras is afforded its age by interpolating the thicknesses of loess between them. This technique, loess-chronometry, has the advantage of ability to measure an interval of tens to thousands years in the geologic past, over radiometric dating. More than 900 tephras are presently recorded and linked each other in a computer database including name, source volcano, age, magnitude, stratigraphy, and remarks. An updated version is listed in WWW at "http://www.la.gunma-u.ac.jp/〜hayakawa/English.html".

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

石崎 泰男 森田 考美 鳥山 光

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.62, no.3, pp.95-116, 2017-09-30 (Released:2017-10-11)

参考文献数

32

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The ca. 17 cal. ka BP eruption at Nantai Volcano, NE Japan, initially produced widespread Plinian fallout deposit (Nantai-Imaichi Tephra:Nt-I) and two overlying associated scoria flow deposits, i.e., dacitic pyroclast-rich, Shizu Scoria Flow Deposit (SZ) and andesitic pyroclast-rich, Takanosu Scoria Flow Deposit (TKS). A∼2.8m thick outcrop of the Nt-I at Nikko City, 7.5km ESE of the volcano, consists of a basal phreatic fall bed (∼2cm thick) and eleven overlying fall units (units 1-11 in ascending stratigraphic order) defined by componentry, size grading, and chemical composition of the pyroclasts. The total lack of clear boundary structures between each unit suggests that the Nt-I was generated by the pyroclasts falling from continuous eruptive column. Grain size analyses of the Nt-I shows that column height rapidly increased and reached its climax soon after the eruption began, and then oscillated slightly and declined until the end of the Plinian phase. The composition of the pyroclasts shows that the Nt-I resulted from the tapping of a stratified magma chamber, in which dacitic magma capped hybrid andesitic magma. Light-colored, microlite-free, dacitic pumice (DWP) predominates from unit 1 through unit 9. In contrast, moderately vesicular andesitic scoria (AGS) is a major constituent of units 10 and 11. Microlite-rich dacitic obsidian (DOB) is present from unit 1 through unit 3, but was not observed above unit 3. Microlite-rich dacitic scoria (DBS) is present from unit 1 through unit 8, and coexists with DOB in single pyroclast. A plausible explanation for the common eruption of a small amount of microlite-rich pyroclasts along with the predominant DWP is that the microlite-rich pyroclasts represent fragments of the degassed margins of the conduit through which the dacitic magma rose. As the eruption advanced, the passageway may have widened, and the microlite-rich magma along the conduit wall was eroded and ejected along with the DWP. The density of the DWP remained constant from unit 1 through unit 8, and then increased at unit 9. The incorporation of slightly denser, dacitic pyroclast into the column is likely to have destabilized the eruption column. The destabilization caused partial collapse of the column and generated the intra-Plinian Shizu Scoria Flow Deposit, whose particle density is similar to that of unit 9. In contrast, the ejection of dense AGS combined with the incorporation of dense lithics into the eruption column is likely to have destabilized the column, and triggered total column collapse that formed the post-Plinian Takanosu Scoria Flow Deposit.

著者

安藤 邦彦

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.41, no.4, pp.199-201, 1996-11-15 (Released:2017-03-20)

参考文献数

6

著者

三村 弘二

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.47, no.4, pp.217-225, 2002-09-17 (Released:2017-03-20)

参考文献数

19

被引用文献数

2

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Nekoma Volcano, situated between Bandai Volcano and the Aizu Basin in northeast Japan, is a composite volcano of andesite to dacite with a total eruption volume of 16 km3. A horseshoe-shaped caldera a few km in radius was formed at the top of the volcano, and the volcanic activity is divisible into the Old Nekoma Volcano established before the caldera forming event from ca. 1 Ma to 0.6 Ma and the New Nekoma Volcano established after the caldera forming event after ca. 0.5 Ma. Old Nekoma Volcano is subdivided into Oguninuma north lava, Hayama lavas, Hagidaira pyroclastic flow (block and ash flow) deposit, Main cone lavas, Oguniyama lavas and Ougigamine lavas, in ascending stratigraphic order. They formed a flat cone-shaped volcano. All but the Ougigamine lavas were produced by summit eruptions and the Ougigamine lavas formed monogenetic volcanoes from several vents on the western flank. New Nekoma Volcano, erupted after Oshizawa debris avalanche deposit, which related to the caldera forming event, is composed of Nekomagatake lavas and 1349 m lavas occurred at the horseshoe-shaped caldera margin.

著者

吉村 俊平

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.61, no.4, pp.605-613, 2016-12-31 (Released:2017-01-13)

参考文献数

37

著者

山﨑 誠子 星住 英夫 松本 哲一

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.61, no.3, pp.519-531, 2016-09-30 (Released:2016-11-08)

参考文献数

33

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Unspiked K-Ar dating procedure enables the correction for mass fractionated initial 40Ar/36Ar ratios, and has been successfully applied to young volcanic samples, especially younger than 0.5 Ma. We reconstructed the growth history of western to central part of Kuju Volcanic Group based on the unspiked K-Ar age data. The unspiked K-Ar ages for the small andesitic-dacitic volcanoes of Stage 1 (Kutsukakesan Volcano, Iozan Lava, Kuroiwasan Volcano, Narukoyama Volcano) provided with two age group of ca. 160-150 and ca. 90-80 ka, suggesting that Stage 1 may be divided into at least two sub-stages. During Stage 3 after the largest eruption associated with Handa pyroclastic flow deposit, some lava domes and stratovolcanoes in the central part (Ogigahana Volcano, Nakadake Volcano and Mimatayama Volcano) were built up from ca. 54 to 34 ka, which is older than the previous interpretation.Based on these K-Ar ages and estimated volume for each volcanic unit, we calculated the magma discharge rate during each volcanic stage and the whole period of the volcano history. The calculated magma discharge rate for Stage 1, 3 and 4 are 0.09, 0.12, 0.18 km3/ky, respectively, showing that the activity has slightly increased. The rate of 0.12 km3/ky for the whole period is similar to that for Aso and Unzen volcanoes lie to the west of this volcano.

著者

松本 亜希子 中川 光弘 井口 正人

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.61, no.3, pp.545-558, 2016-09-30 (Released:2016-11-08)

参考文献数

38

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On the 24th July, 2012, a large scale explosion occurred at Minamidake Summit crater of Sakurajima volcano, for the first time in last 1.5 years. This eruption is characterized by a clear, large preceding inflation ca.22 hours before the eruption. The juvenile glass particles in the volcanic ash of this eruption have less amount of microlite than those of Showa crater. The crystal size of microlite is also smaller. In contrast, their microlite number densities (MND) of plagioclase and pyroxenes are similar to those of Showa crater. According to the results of the decompression experiments by previous studies, the variations of crystallinity of microlite with the constant MND can be explained by the difference in the length of the duration for decompression, and/or the duration until the quench after the decompression. Considering these results, the juveniles of the summit eruption are derived from the eruption induced by relatively rapid decompression with rapid quench, and the juveniles from Showa crater are the products of the eruptions accompanied with the relatively slower decompression and/or the longer annealing after decompression. Therefore, it is interpreted that the 24th July, 2012 eruption was caused by rapid magma ascent with much shorter stagnation in the conduit. In contrast, the eruptions at Showa crater might have been induced by slower magma ascent and/or longer stagnation at a shallower depth of the conduit. This interpretation agrees with the data of geophysical observations. On matrix glass chemistry, juveniles of this summit eruption show the distinct trend from those of Showa crater. This feature can be produced by the difference in mode of microlite, which are crystallized during magma ascent. Accordingly, it is possible to evaluate the difference in magma ascent process, using the matrix glass chemistry.

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

津久井 雅志

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.56, no.2, pp.89-94, 2011-06-30

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Old historical documents on 1779 AD An'ei eruption of Sakurajima, southwest Japan were collected from distal places as well as those from neighboring area of the volcano. These records revealed that the ash-fall front traveled to the northeast at about 50-100km/h, reached as far as Tohoku district 1200km from Sakurajima, and covered area of ca. 2.33×10^5km^2. Investigation of old documents helped to improve understanding of behavior of the volcano and environmental effects at the time of infrequent and great eruption. The wide distribution of ash-fall in 1779 Sakurajima eruption suggests that there is a high potential that ash discharged by future eruption of Sakurajima may cover down through the mainland of Japan. We should keep in mind both physical and economical effects of ash-fall in assessing the activity and making the scenario of an eruption.

著者

兼岡 一郎 羽生 毅

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.4, pp.145-150, 1993

著者

早川 由紀夫

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.36, no.3, pp.357-370, 1991-10-15

被引用文献数

4

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The recent progress of physical volcanology is reviewed focusing on studies on volcaniclastic flows and their deposits. Pyroclastic flows are high-particle-concentration, laminar currents with gas as a continuous phase. Pyroclastic surges are low-particle-concentration, turbulent currents with gas as a continuous phase. Lahars are flows of debris with liquid water as a continuous phase. Debris avalanches are catastrophic landslides in which a continuous phase is absent or plays no role for the motion. Owing to the upward gas flow, fluidization processes operate in pyroclastic flows. Flow behavior and resultant deposits are remarkably different depending the degree of fluidization, because it effectively reduces the yield strength of the flow. However, the distance traveled is slightly affected by the degree of fluidization. It is determined mainly by the mass incorporated at the source or by the velocity acquired when it wes initiated.

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

林 信太郎

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.43, no.4, pp.207-212, 1998

参考文献数

19

被引用文献数

1

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Kampu volcano is a small stratovolcano situated at the central part of Oga Peninsula, Akita Prefecture. In 1810, an earthquake as large as M 6.5 occurred near this volcano. Yoshimasa Satake, the lord of the Akita clan, wrote two official reports to the Tokugawa shogunate. They included eruption records of Kampu volcano: "Yamayake" and "Yamayakekuzure". These words were usually used for the eruption during Edo period and mean that the mountain was firing. Several reliable documents, which was written at Oga Peninsula included no eruption record. In addition, there is no eruption record in the note of Yoshimasa Satake, which is thought to have used for making the two official reports. It is concluded that the eruption descriptions of 1810 Kampu is false and created by Yoshimasa Satake at Akita clan office at Edo (Tokyo). The false eruption might have been created to make the exaggerated damage report of earthquake.

著者

高橋 正樹

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.39, no.4, pp.207-218, 1994-09-20

被引用文献数

4

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Late Quaternary poly genetic volcanoes in Japanese islands can be classified into two types : P-type and O-type. The vent of the P-type (parallel types) aligns in parallel with the orientation of regional σ_<Hmax>, while the vent alignment of the O-type (oblique type) is normal or highly oblique to it. The P-type consists of three sub-types based on the kind of associated active faults : PN (with normal faults), PS (with strike-slip faults), and PR (with reverse faults). Most of the O-type are constructed on the mountain range which is bounded on both side with reverse faults ; its vent alignment is probably controlled by the local extensional stress field in the mountain mass caused by the gravity tectonics. Thin sheet-like magma chambers are estimated to be present beneath the O-type volcanoes ; the arrangement of maximum principal stress axis producing reverse faults (σ_v=σ_3) favors the formation of sheet-like magma chambers. The eruption rate of the O-type is generally small because of the complexity of its magma plumbing system.