著者

安井 真也 高橋 正樹 石原 和弘 味喜 大介

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.52, no.3, pp.161-186, 2007-06-29 (Released:2017-03-20)

参考文献数

49

被引用文献数

4

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The 1914-1915 Sakurajima eruption was the largest eruption in Japan in the 20th century and erupted andesitic magma was about 1.5km3 DRE (Dense Rock Equivalent) in volume. Pumice fall and lava flows were generated from the fissure vents on the western and the eastern flanks of the volcano and pyroclastic cones were formed around the vents. Eruptive style changed with time. It is divided into three stages. After the initial, vigorous, Plinian eruption of about 36 hours (Stage 1), extrusion of lava associated with intermittent ash-emitting eruptions with or without detonations lasted for about 20 days on both sides (Stage 2), followed by an outflow of lava for more than 1.5 years on the eastern side (Stage 3). Consequently, the vast lava fields, which consist of a number of flow units formed on both sides of the volcano. Some units of lava show evidence of welded pyroclastic origin, suggesting clastogenic lava. In the western lava field, surface blocks characteristically consist of pyroclastic materials which show variable degrees of welding even within a single block. Typical eutaxitic textures and abundant broken crystals are also recognized under the microscope. Some flow units can be traced upstream to a pyroclastic cone. These features indicate that many flow units of lava on the western flank are clastogenic, which were generated by the initial, Plinian eruption of Stage 1. In the eastern lava field, evidence of pyroclastic origin is rarely discernable. However, the content of broken crystals varies widely from 20% to 80% in volume. Most lava flows, which were erupted in Stage 2 associated with frequent ash-emitting eruptions, contain broken crystals more or less than 50%. This fact indicates that magma in the conduit experienced repetitive fragmentation and coalescence due to intermittent explosions prior to outflow. Lava flows of Stage 3 contain much smaller amounts of broken crystals indicating gentle outflow of coherent lava. Relatively large-scale lava deltas developed toward the sea in the eastern lava field. Eyewitness account at that time reports that ocean entry of lava from several points started several months after the beginning of Stage 3. Although small-scale breakouts formed at the flow fronts of some lava on both sides, a large volume of the deltas can not be accounted for by secondary breakouts of ponded lava within the precedent flow lobes. It is considered that lava tube system fed lava to form the lava deltas.

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.第2集 (ISSN:24330590)

巻号頁・発行日

vol.28, no.3, pp.263-273, 1983-10-01 (Released:2018-01-15)

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The Chuseri pumice is a widespread Holocene dacitic tephra layer erupted from the Nakano Umi crater in the Towada caldera. The pumice is directly overlain by the Kanegasawa bedded pumice and Utarube ash. The Chuseri pumice. Kanegasawa pumice, and Utarube ash define the Chuseri tephra formation. Volumes are calculated using isopach maps to be 6.5 km^3 for the Chuseri pumice, 1.2 km3 for the Kanegasawa pumice, and 0.9 km3 for the Utarube ash. Plots of the areas enclosed by the isopleths of maximum pumice size and maximum lithic size show the Chuseri pumice to be an average plinian eruption product. The Utarube ash is an ash-fall deposit containing accretionary lapilli and is interbedded with surge deposit near source area. Grainsize characteristics of the Chuseri pumice are described. Like other plinian deposits, the Chuseri pumice does not contain an appreciable amount of fine ash (finer than 1/16mm), at least, as far as 45 km from the source vent. A new radiocarbon date (GaK-9761) on charcoal from within the Chuseri pumice deposit establishes an age for the eruption of 5,390±140 years B.P.

著者

第四紀火山カタログ委員会

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.6, pp.285-289, 1999-12-29 (Released:2017-03-20)

参考文献数

4

著者

河又 久雄 高橋 正樹

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 1994.2 (ISSN:24335320)

巻号頁・発行日

pp.169, 1994-10-20 (Released:2017-02-10)

著者

河又 久雄 高橋 正樹

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 1993.2 (ISSN:24335320)

巻号頁・発行日

pp.95, 1993-10-04 (Released:2017-02-10)

著者

谷口 宏充 伊藤 順一 中川 光弘 三軒 一義

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 1994.2 (ISSN:24335320)

巻号頁・発行日

pp.68, 1994-10-20 (Released:2017-02-10)

著者

小林 哲夫 奥野 充 ミラブエノ マリア ハナ

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.59, no.4, pp.299-303, 2014-12-31 (Released:2017-03-20)

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 (ISSN:04534360)

巻号頁・発行日

vol.59, no.1, pp.25-29, 2014-03-31 (Released:2017-03-20)

著者

石崎 泰男 森田 考美 岡村 裕子 小池 一馬 宮本 亜里沙 及川 輝樹

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.59, no.3, pp.185-206, 2014-09-30 (Released:2017-03-20)

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Nantai volcano (2,486m a.s.l.), a near-conical stratovolcano with a summit crater ~1km wide, is located along the volcanic front of NE Japan. To date, the eruptive history and characteristics of this volcano have been poorly studied, except for an explosive eruption that occurred at ~17 cal. ka BP (Stage 2 eruption). In this paper, we present the results of investigation of the stratigraphy of recent proximal eruption products, the tephrostratigraphy of the northeastern foot of the volcano, and new radiocarbon ages. The results show that at least six eruptions of Nantai volcano have occurred after Stage 2 eruption, and we refer to these as Stage 3 eruptions. We identify four tephra layers and one pyroclastic flow deposit in the soil sections above the Stage 2 pumice flow deposit, at the northeastern foot of the volcano. These are classified in the ascending order as: (1) Nantai-Bentengawara Tephra 4 (Nt-Bt4), (2) Bentengawara Pyroclastic Flow Deposit, (3) Nt-Bt3, (4) Nt-Bt2, and (5) Nt-Bt1. The Nt-Bt2 is phreatic fallout with no juvenile material; the other tephra layers are phreatomagmatic fallouts containing juvenile pyroclasts together with ash aggregates. Six Stage 3 eruption products are identified within and around the summit crater: (1) a blocky lava flow (Osawa Lava) exposed on the northern crater wall, (2) a partly dissected scoria cone and (3) a poorly-preserved tuff ring (and its resedimented deposits) on the steep crater floor, (4) a subaqueous lava and associated lava fragments sandwiched by lacustrine deposits, (5) a tuff breccia containing hydrothermally-altered lava block and clayey matrix, and (6) a stratigraphically uppermost phreatomagmatic tephra (Nantai-Yudonoyama Tephra). All the proximal eruption products, except for the subaqueous lava, can be correlated with the tephra layers and the pyroclastic flow deposit on the northeastern foot based on stratigraphic positions, lithologies, and geochemical affinities. Our study reveals that five tephra-forming eruptions (ca. 14, 12, 8, 7.5, and 7 cal. ka BP) and one non-explosive subaqueous eruption (between 12 and 8 cal. ka BP) occurred during Stage 3, from a discrete eruption center inside the summit crater. Moreover, the tephra-forming eruptions were diverse in style, with strombolian (12 cal. ka BP), phreatomagmatic (14, 8, and 7 cal. ka BP), and phreatic (7.5 cal. ka BP) eruptions. Eruption style was determined primarily by vent position and spatiotemporal variations in local hydrological factors (e.g., the presence or absence of a crater lake, wet lacustrine deposits, and streams).

著者

松本 哲一 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 (ISSN:04534360)

巻号頁・発行日

vol.44, no.1, pp.1-12, 1999-03-05 (Released:2017-03-20)

参考文献数

12

被引用文献数

4

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A systematic K-Ar age determination has been made on thirty-seven samples from the Older Ontake volcanic products, Ontake Volcano, central Japan, with analytical uncertainties mostly within ±5% (1σ level). The “Kuragoehara Lava”, which the previous researchers used as a key bed for stratigraphic correlation, gives significantly different eruption ages in each disthbution area, and some lavas classified into the same stratigraphic units among each area also show quite diffrent K-Ar ages. Hence, a revised volcano-stratigraphy is proposed based on the radiometric data obtained in the present study. The Older Ontake Volcano may be a compound volcano consisting of more than four stratovolcanoes with different vents. The first one, “;Tobu Volcano Group”, erupted at around 750-650 ka on the wide eastern side. The second one, “Tsuchiurazawa Volcano”, erupted at around 680-570 ka mainly in the western area. The third one, “Uetawarayama Volcano”, produced lavas at around 540-520 ka, and the products filled along valleys in the western area. The last one, “Mikasayama Volcano” erupted at around 440-420 ka in the southeastern area. The inactive period between the Older and Younger Ontake volcanic products continued for more than three hundred thousand years. The present study has revealed that the K-Ar age determination is effective for estimating a time gap between the Quatermary volcanic products whose stratigraphic relation can not be well defined in field.

著者

筒井 智樹

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.50, no.Special, pp.S101-S114, 2005-12-20 (Released:2017-03-20)

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Recent achievements in seismic studies of volcanic structure are summarized in this article. Seismic studies of volcanic structure was enhanced and advanced extensively in 1990's. The advance of the study was supported by new compact and light weighted digital recorders and by popularization of 3-D travel time inversion algorithm. Seismological characters in volcanic structure were revealed and were represented as high and low velocity anomalies, concentrated seismicity and intra-crust seismic reflectors. Important problems for seismic studies of volcanic structure are presented as more penetration, more resolution and more quantification of seismic characters in active volcanoes, which should be solved in next decade.

著者

萬年 一剛

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:21897182)

巻号頁・発行日

vol.48, no.6, pp.425-443, 2003-12-25 (Released:2017-03-20)

著者

安井 真也 富樫 茂子 下村 泰裕 坂本 晋介 宮地 直道 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.43, no.2, pp.43-59, 1998-04-30 (Released:2017-03-20)

参考文献数

22

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A large amount of pyroclastic materials (ca. 1.7 km3) was erupted during the 1707 eruption of Fuji Volcano. Variety of lithic fragments has been recognized in the pyroclastic fall deposits, namely, accessory and accidental lava fragments, gabbros, and granitoids. A great variety of petrologic features is observed in gabbroic fragments consisting of olivine gabbro norite, gabbro norite, troctolite and anorthosite. The gabbros are divided into O, P and F groups on the basis of modal ratios of olivine, plagioclase and Fe-Ti oxide. O group mainly consists of plagioclase and olivine with minor amounts of pyroxenes and Fe-Ti oxide. O group is considered to have been adcumulated in the lower part of magma chamber because of their high depletion in incompatible elements, their well-sorted grain size and sedimentary structure. P group is composed of plagioclase, pyroxenes and minor amounts of olivine and Fe-Ti oxide. F group is similar to P group, but is enriched in Fe-Ti oxide. P and F groups are orthocumulates and may be solidified in the upper part and margin of magma chamber or dike because of their porphyritic texture. Such a variety of gabbros may correspond to the difference in location of the single gabbroic body beneath Fuji Volcano. The estimated source magma of the gabbros is similar to the basalt of Fuji Volcano in chemical and mineralogical compositions indicating that they are cognate origin. Chemical compositions of olivine and pyroxenes become magnesian and those of plagioclase become calcic with the decreasing of bulk-rock FeO*/MgO ratio. It suggests that they are the products of continuous fractional crystallization. The magma of the 1707 eruption could have come up from under the gabbroic body, which was the solidified basaltic magma chamber, and have caught and brought the rocks from the gabbroic body up to the surface as cognate xenoliths during the eruption.

著者

和田 恵治 佐藤 鋭一 佐野 恭平 向井 正幸

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 2011 (ISSN:24335320)

巻号頁・発行日

pp.2, 2011-10-02 (Released:2017-02-10)

著者

中野 俊 伊藤 順一

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.43, no.3, pp.123-126, 1998-06-10 (Released:2017-03-20)

被引用文献数

1

著者

濁川 暁 野上 景子 石崎 泰男

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 2013 (ISSN:24335320)

巻号頁・発行日

pp.120, 2013-09-29 (Released:2017-02-10)

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.62, no.3, pp.117-134, 2017-09-30 (Released:2017-10-11)

参考文献数

25

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The Asama-Maekake volcano has been active for about 10,000 years. Although the many pyroclastic fall deposits, which mainly consist of pumice fall layers, are indicative of past sub-Plinian eruptions, the stratigraphy of the deposits over the entire history of the Asama-Maekake Volcano has not yet been revealed. This is because the pyroclastic fall deposits are distributed in the various directions from the crater. Moreover, the deposits predating the 12th century have a similar occurrence and petrography, making it difficult to correlate deposits among different localities. Therefore, little information is available for the older eruptions. The pyroclastic fall deposit in the direction not leeward of the dominant wind is focused in this study. A pyroclastic fall deposit called Miyota pumice (referred to as As-My hereafter), which is characteristically distributed in the southern direction from the crater, was targeted. The distribution of As-My has barely been mapped owing to the difficulty resulting from its poor exposure. The 14C ages of the samples of black humus soil immediately beneath As-My at two localities were dated to 5720±30yBP and 5530±30yBP. These ages are almost the same as those of the pyroclastic fall deposits As-UB (Ubagahara) and As-Kn (Kuni) distributed on the northern flank. Since the stratigraphic relation among these deposits is difficult to determine, it is not clear whether As-My, As-UB, and As-Kn are products from a single eruption or different eruptive activities. At least, it can be considered that multiple sub-Plinian eruptions occurred around 6,000 years ago. In addition, black humus soil and intercalating four pumice fall deposits including As-My at a major outcrop on the SSE flank slope (Locality M72) provided information on the activity over the last 8,000 years, back to the earliest stage of the volcano. The 14C ages of samples of black humus soil taken from immediately beneath the pumice fall deposits were 3,830±30yBP, 4,710±30yBP, 5,530±30yBP (just beneath As-My), and 7,470±30yBP. This is the first time that such sequential data concerning eruptive ages on the flank slope has been obtained. Black soil contains angular lithic fragments, which are similar to the ash grains from Vulcanian eruptions (e.g., the 2004 eruption). This suggests that Vulcanian eruptions have occurred between sub-Plinian eruptions since the early stage of the Asama-Maekake volcano. Such information from outcrops on the flank slopes with various directions is required to reconstruct the detailed eruptive history.

著者

中川 光弘 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.38, no.4, pp.139-144, 1993-09-30 (Released:2017-03-20)

参考文献数

3

著者

古川 竜太 高田 亮 A. NASUTION

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 2005 (ISSN:24335320)

巻号頁・発行日

pp.127, 2005-10-05 (Released:2017-02-10)

著者

長橋 良隆 小林 聡子 奥平 敬元 吉川 周作 吉田 武義 里口 保文

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.2006, 2006