著者

源内 直美 平松 良浩 河野 芳輝

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.5, pp.411-418, 2002-11-29 (Released:2017-03-20)

参考文献数

26

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A three-dimensional density structure in the shallower crust beneath the Hida Mountains, central Japan, is estimated by using gravity data. We employed seismic velocity structure models both as an initial condition and constraints of gravity structure models. We estimated that an extremely low-density body (density is smaller than 2.1 g/cm3) exists at 4-8 km depth (2 to 6 km below the sea level) beneath Mt. Tateyama (3,015 m) and also along the Hida mountains. Estimated horizontal extent of the body is about 14 km in east to west, about 28 km in north to south directions, respectively, and about 4 km in thickness. The volume of the body is about 1,000 km3. Spatial distribution of the extremely low-density body is well consistent with a low velocity region estimated from studies of seismic tomography.

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:24330590)

巻号頁・発行日

vol.17, no.1, pp.33, 1972-06-01 (Released:2018-01-15)

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:24330590)

巻号頁・発行日

vol.12, no.2, pp.90, 1967-08-01 (Released:2018-01-15)

著者

藤野 直樹 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 (ISSN:04534360)

巻号頁・発行日

vol.42, no.3, pp.195-211, 1997-06-30 (Released:2017-03-20)

参考文献数

26

被引用文献数

3

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Kaimondake Volcano, situated in the Ibusuki Volcanic Region of southern Kyushu, is an undissected volcano which consists of a basal stratovolcano and a small central volcano. We established the eruptive history of this volcano by tephrochronology. Kaimondake Volcano started its eruption ca. 4 ka, and the latest eruption occurred in A. D. 885 (ca. 1.1ka). For about 2,900 years during this period, the volcano had been active, and 12 major eruption deposits (Km 1-Km 12) were recognized. The repose periods between these eruptions were estimated to range from 100 to 400 years. The mode of eruption of this volcano was mainly scoriaceous sub-plinian type, and was frequently associated with phreatomagmatic eruptions because the volcano originated from the shallow sea or near-shore environment. Lava flows were often associated with the scoria eruptions. Submarine lava flows which flowed southeastward are topographically divided into three; among them the lowest one is the most voluminous and is thought to have flowed out in the early stage, probably before Km6 eruption period. Among the 12 major eruption deposits, Km1, Km9 (ca. 2 ka), Km11 (ca. 1.5 ka), and Km12 (ca. 1.1 ka) were voluminous, and largely contributed to the formation of the volcanic edifice. During the latest eruption (Km 12), a central volcano was formed in the summit crater. This central volcano is not a simple lava dome, but a mound of complex volcanic materials with a composite structure. It consists of a basal scoria cone associated with fluid lava flows, which is later capped by viscous lava dome, and then subsequently penetrated by volcanic plug around the summit. The summit crater, which is named Hachikubo, had been thought to be a collapse crater, but it was geologically proved to be a large explosion crater which was successively enlarged during the eruption of Km12a. The total amount of volcanic products was calculated to be 3.1 km3 and 2.3 km3 for tephra and lava flows, respectively. Although there are no systematic relations between eruption volumes and the preceding repose period, the eruption materials containing tephra were more voluminous in the later stage than in the early stage, while those of lava flows were exceptionally large in the early stage of volcanic history.

著者

小林 淳 青木 かおり 村田 昌則 西澤 文勝 鈴木 毅彦

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.65, no.2, pp.21-40, 2020-06-30 (Released:2020-07-06)

参考文献数

35

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This study established tephrostratigraphy and clarified the eruption history of Niijima volcano (Izu Islands, Japan) after the Miyatsukayama event (12.8-8.5calka) through geological survey around the central and northern parts of Niijima island, and Shikinejima and Jinaijima islands. Detailed explanation is summarized below. The Miyatsukayama eruptive event started at the north of Akazakinomine lava dome (central part of Niijima island) at 12.8calka. The series of eruptions formed Miyatsukayama lava dome, and produced Nj-MtG tephra (12.8-8.5calka) and K tephra (ca. 8.5calka). In particular, the first pyroclastic density current covered the Akazakinomine lava dome thickly, accompanying fallout deposits (Nj-Mt tephra) which were widely distributed in the northern part of Izu Islands. Subsequently, the Shikinejima event ejecting Nj-Sk tephra occurred at ca. 8calka. At ca. 7.5calka, H(s) tephra was produced by the eruption near Shikinejima island, and H(n) tephra was produced by the Niijimayama event. During the Miyatsukayama-nanbu event (ca. 5.5calka) producing Nj-Mt(s) tephra, pyroclastic density currents erupted from the southern part of Miyatsukayama lava dome, buried depressions on the Miyatsukayakma lava dome and formed horizontal and flat surface. The erupted pyroclastic material covered the Akazakinomine lava dome widely and formed pyroclastic cones and lava domes near the source. After that, the Wakago event (Ni-Wg tephra), the D tephra event and the Kudamaki-Atchiyama event (Nj-KdAt) erupted basaltic magma at ca. 3.6calka, ca. 1.6calka and AD 856-857, respectively. Several decades after the Kudamaki-Atchiyama event, the Mukaiyama event (Nj-My) occurred at the southern part of Niijima island in AD 886-887. The Mukaiyama event is the largest eruption during the last 12.8 kys. At Niijima Volcano, eruptions with the magnitude equivalent to the Mukaiyama event (>0.1DREkm3) have occurred every thousand years since the Miyatsukayama event, and the large area of the island was covered with pyroclastic density currents at each eruption.

著者

長井 雅史 小林 哲夫 三輪 学央 棚田 俊收 上田 英樹

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 2016 (ISSN:24335320)

巻号頁・発行日

pp.157, 2016 (Released:2017-02-07)

著者

西村 裕一 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 (ISSN:04534360)

巻号頁・発行日

vol.44, no.1, pp.41-43, 1999-03-05 (Released:2017-03-20)

参考文献数

3

被引用文献数

1

著者

早川 由紀夫 井村 隆介

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.1, pp.25-35, 1991-04-15 (Released:2017-03-20)

被引用文献数

1

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The eruptive history of Aso volcano for the past 80,000 years is revealed by tephrochronology and loess-chronometry. Around the Aso caldera is a thick accumulation of loess, which is intercalated with numerous Aso tephra layers of limited dispersal as well as three widespread tephra layers of known age that are good marker horizons ; the Akahoya ash (6.3 ka), the Aira-Tn ash (22 ka), and the Aso-4 ignimbrite (70 ka). Loess-chronometry is based on the assumption that, in the Aso region, the accumulation rate of loess has been constant as 12 cm/ky from 80 ka to the present. Most of tephra layers after the caldera-forming Aso-4 eruption are composed of volcanic sand or scoria lapilli of basaltic andesite composition. However the 27 ka Kusasenri dacite (SiO2 = 67%) pumice is a conspicuous exception. The large volume of 5.85 km3 (bulk) and wide dispersal of this pumice suggests that it is a product of plinian eruption. From October 5 to the end of November 1989, the Nakadake crater of Aso volcano was in eruption. Ash was uninterruptedly emitted from a 500-1,000 m high eruption column coming out of the crater. The average discharge rate of ash was 5 × 107 kg/day. The total mass of ash discharged during the two months reached 3 × 109 kg. The penultimate eruption in recent history was June-August 1979, when 7.5 × 109 kg of ash was discharged. Outside the Aso caldera, the thickness of the 1989 ash is less than 1 cm. It is almost impossible to detect an old ash layer of thickness about 1 cm in a loess cross section, suggesting that sedimentary records 10 km away from a volcano are insufficient to reconstruct past eruptions smaller than 1010 kg. Eruptions smaller than 1010 kg can be determined only from proximal deposits. The history of eruptions of Aso volcano over the last few thousand years is tentatively determined from cross sections 2-4 km west of the Nakadake crater. After a 580-1,250 year dormant period, Aso volcano became active about 1,780 years ago. From then, small eruptions each with 109-1010 kg ash discharge have been repeated 48-88 times up to the present. The duration of each eruption was a few months, and the dormant interval between eruptions averaged 20-37 years.

著者

櫻井 亮輔 中村 美千彦 奥村 聡 無盡 真弓 中谷 貴之

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 2018 (ISSN:24335320)

巻号頁・発行日

pp.200, 2018 (Released:2019-03-06)

著者

安井 真也

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.60, no.2, pp.269-274, 2015-06-30 (Released:2017-03-20)

著者

横尾 亮彦 市原 美恵 谷口 宏充

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.299-304, 2004-10-29 (Released:2017-03-20)

参考文献数

24

被引用文献数

1

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Izu-Oshima volcano, one of the most active volcanoes in Japan, started a series of emotions on Nov. 15, 1986. One of the characters of the e ructions is the small-scale explosions with flashing arcs, which were the visualized shock waves as a phase change of H2O in the air. occurred at the summit lava-lake. The flashing arcs, seen on the movie, show several characteristics; 1) they spread and propagate semi-spherically, and 2) the launching of semi-spherical ballistics follows the flashing arcs. Analysis of the movie indicates that the velocities of flashing arcs were 300-440 m/s and their sources were located almost on the surface of the lava-lake. We paid attention to the ballistics in the light of scaling laws, which were established from field explosion experiments, so that we were able to estimate explosion energy as about 8×109J. Additionally, assuming that the flashing arcs were produced by an explosion, such as a bursting of pressurized-bubbles, we could get information of their condition, a relationship between inner-pressure and the size.

著者

伊藤 順一

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 2016 (ISSN:24335320)

巻号頁・発行日

pp.69, 2016 (Released:2017-02-07)

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

荒牧 重雄 藤井 敏嗣

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:24330590)

巻号頁・発行日

vol.33, no.SPCL, pp.S297-S306, 1988-06-30 (Released:2018-01-15)

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Detailed characterization of the whole rock composition of the ejecta of the 1986-1987 eruption of Izu-Oshima volcano by the XRF technique (FUJII et al., 1988) clearly indicates that the ejecta from the central crater of Miharayama (Crater A) are different from those erupted from the fissures (Fissures B and C) on the caldera floor and on the outer slope of the main stratovolcano. This suggests that the conduits which led the A and B, C magmas to the surface were separated physically from each other down to a certain depth. The ejecta from A crater resemble closely to those erupted during the past 1300 years (Y magmas) while the ejecta from B and C fissures are unique in composition among the Izu-Oshima magmas. The A and Y magmas are Fe-enriched island arc type tholeiites that must have been derived from the primary tholeiite magmas through crystal fractionation of olivine, pyroxenes and plagioclase. The B and C magmas can be derived simply through crystal fractionation of A or Y magmas leading to Fe-enriched basaltic andesites, andesites and dacites. This strongly suggests that an isolated pocket of magma starting with a composition of Y underwent strong fractionation to produce volatile enriched ferroandesitic magma. This body of magma was probably activated by the sudden depressurization caused by shattering and fissuring of the crust to form a 1500 m high fire fountains and to produce a sub-Plinian scoria fall deposit. The vent of A crater must have been stable at least during the last 1300 years and directly, or through the subsidiary magma chamber(s), connected to the main chamber above the Moho, where an extensive crystal fractionation has been taking place to produce Y magma from the parent tholeiitic magma. Marked ground depression and extension and migration of seismicity observed during the eruption suggest a possibility that a substantial amount of additional magma was intruded to form a NW-SE trending dike during the peak phase of the eruption. This is in harmony with the Nakamura’s model of the volcano with the NW-SE trending dike swarm which is controlled by the regional compressional stress field. However, gravity and some other grophysical data suggest that the deformation could have been the result of underground cracking without magma injection. Our model is not conclusive on this matter and the expectation that this eruption will eventually lead to the large-scale activity that has been recurring in every 130±50 years is yet to be tested.

著者

金子 隆之 大湊 隆雄 武尾 実 小山 崇夫 前野 深 安田 敦 中田 節也 渡邉 篤志 高木 朗充 長岡 優

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 2016 (ISSN:24335320)

巻号頁・発行日

pp.125, 2016 (Released:2017-02-07)

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

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

中坊 真 迫 幹雄 吉川 慎 増田 秀晴 外 輝明 橋本 武志 ディアゴ ファン カルロス 長谷 英彰 小野 博尉 須藤 靖明 筒井 智樹 吉川 美由紀 ガルセス ミルトン 田中 良和 西島 潤 米重 和馬 川口 昌宏 工藤 貴久 藤光 康宏

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.1998, 1998

著者

木股 文昭

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.2015, 2015