著者

長橋 良隆 里口 保文 片岡 香子

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.2014, 2014

著者

工藤 崇

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.55, no.2, pp.89-107, 2010-04-30 (Released:2017-03-20)

参考文献数

39

被引用文献数

1

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Towada volcano is an active volcano located in the northern part of the Northeast Japan arc. Ogurayama Lava Dome (OLD), which is a dacitic lava dome located near the center of Towada volcano, has been regarded as a product of the latest eruptive episode A. In this paper, the author reports that the OLD is older than previously thought and that it was formed at the end of eruptive episode D'. The OLD overlies pyroclastic deposits of the eruptive episode E and is overlain by pyroclastic deposits of the eruptive episode C. These stratigraphic relations restrict the eruption age of the OLD to 9.2-6.2cal kyr BP. Within this time interval, two eruptive episodes (D' and D) are recognized as tephra fall deposits in the distal area. The distribution of Herai Ash from the eruptive episode D' shows that the source vent is located in the vicinity of the OLD. Furthermore, the petrological features of the OLD closely resemble those of the Herai Ash. These observations indicate that the OLD is the product of the eruptive episode D' (7.5cal kyr BP). The probable eruption sequence of the eruptive episode D' is as follows. Intermittent phreatomagmatic eruptions occurred in the earliest stage. These eruptions produced the lower part of the Herai Ash. Subsequent lava eruptions formed the OLD and accompanied intermittent vulcanian eruptions produced the main part of the Herai Ash. The source vent of the eruptive episode A is not the Ogurayama, because the Ogurayama was formed before this episode. Since the only crater topography currently recognized in the Towada volcano is the Nakanoumi crater (NC), the source vent of the eruptive episode A is considered to be the NC. Since the NC has been the main crater throughout the post-caldera stage, future eruptions will probably occur in the NC. There is the current NC at the bottom of the lake of 320m in depth. A detailed examination of probable eruption style in the future will be required for predicting volcanic hazard of Towada volcano.

著者

鹿野 和彦

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.50, no.Special, pp.S253-S272, 2005-12-20 (Released:2017-03-20)

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This paper gives a brief review on the gravity flows sourced from volcanoes on land and under water. Pyroclastic flows are supported by internal gas and the air incorporated during flowage and run out a long distance as density currents. Ash-cloud umbrella is a special case of density current and the particle fallout from the umbrella is a transition to a dilute, pyroclastic density current. Subaqueous equivalents of pyroclastic flows are supported by internal gas and/or the water incorporated during flowage and are thus interpreted as either subaqueous pyroclastic flows in the strict sense or eruption-fed density currents. Debris avalanches and lahars are also important elements of volcaniclastic gravity flows both on land and under water. These pyroclastic and volcaniclastic gravity flows are thought to transform into traction-dominated flow, particle dispersion-dominated flow (grain or granular flow), fluid escape-dominated flow, or debris flows during flowage in response to the changes mainly of flow velocity, particle concentration, and shear stress. The details of these processes still remain in debate. The role of the heat in pyroclastic density current and subaqueous eruption-fed density current is a future subject to be solved.

著者

小室 裕明 志知 龍一 和田 浩之 糸井 理樹

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.41, no.1, pp.1-10, 1996-03-05 (Released:2017-03-20)

参考文献数

31

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Sanbe Volcano is a large lava dome, 2 km in diameter, emplaced at the center of an elliptical caldera with a long axis of 7 km and a short axis of 5 km. One crater is exposed in the center of this dome, and four peaks surround this crater. However, the basement depth of the caldera has not been determined. We have made gravity measurements around Mt. Sanbe in order to investigate the caldera morphology. The residual gravity anomaly (which is obtained after the regional gravity trend is taken away from the Bouguer anomaly, assumed to be 2.67 g/cm3 in density) is low at the center of Sanbe Caldera. Mass deficiency, estimated by Gauss's theorem, indicates that Sanbe Caldera is one of the low anomaly type calderas, as large as the Mashu caldera. Basement depression under Sanbe Caldera has been determined by three dimensional analysis, when the density contrast between the basement rocks and Sanbe volcanic rocks is 0.43 g/cm3. The depression is square shaped, with a steep rim and a flat floor. The square outline suggests that the depression part may be subsided along normal faults ; accordingly this caldera may have originated in a cauldron. The western and eastern rims of the depression correspond to the somma, but the northern and southern rims are discordant. The poor topographic expression in these areas may be due to collapse of the caldera walls. The deepest part of the basement is centered on the east side of the present crater. This deep center may be the only vent of Sanbe Volcano, because other depressions are not observed beneath the lava dome.

著者

三宅 康幸 齋藤 美由紀 竹下 欣宏 及川 輝樹 齋藤 武士

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.54, no.4, pp.163-173, 2009-08-31 (Released:2017-03-20)

参考文献数

29

被引用文献数

1

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Nantai Volcano is a symmetrical stratovolcano, situated in the southern part of the Northeast Japan arc. Many geologic studies hitherto have suggested that the stratovolcano was formed during the Main stage, and the overlying pyroclastic materials and a lava flow were formed in the Later stage. Because no sedimentary gap is found between any deposits of the Later stage, it is inferred that all of the activity in the Later stage took place successively around 12ky BP (15-14 cal ka BP) and went dormant until now. However, we found a pyroclastic flow deposit named Bentengawara Pyroclastic Flow Deposit (BPFD) at the northeastern flank of the Nantai volcano about 2km from the summit crater. This deposit overlies an 80cm thick deposit of weathered ashy sediments that in turn overlies the Arasawa Pumice Flow Deposit, a member of the Later stage. The lower half of the BPFD consists of volcanic lapilli and ash that is remarkably fine-depleted while the upper half contains abundant scoria of mainly lapilli-block sized clasts. The deposit also includes a small number of breadcrust blocks and occasional accessory lava blocks and fragments of charred wood. The breadcrust blocks consist of a dense outer crust that is significantly fractured and a vesiculated interior. It is noteworthy that the edges of the cracks are sharp and never rounded, suggesting that the vaporization of the inner magma that produced these cracks took place just before or immediately following the settlement of the blocks. Paleomagnetic data from three breadcrust block samples indicate that the magnetic vectors of high temperature components are aligned with our present-day poles. Two pieces of charred wood were measured for their 14C ages with results of 12-11 cal ka BP. The whole rock chemistry of scoria and breadcrust blocks are determined to be significantly different from any of the rocks of the Later stage, but the accessory block in the BPFD has the similar chemistry to the Osawa Lava, the last product of the Later stage. We therefore suggest that the BPFD was deposited after the Later stage with a short (~3ka) dormant period between them. Since the age is possibly around 10ka, the Nantai volcano should be counted as active volcano based on the definition provided by the Meteorological Agency of Japan.

著者

鎌田 浩毅 星住 英夫 小屋口 剛博

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 1987.2 (ISSN:24335320)

巻号頁・発行日

pp.85, 1987-10-05 (Released:2017-02-10)

著者

ラカンナ ジョルジオ 市原 美恵 岩國 真紀子 武屋 実 井口 正人 リペペ マウリチオ

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.2012, 2012

著者

西村 太志 井口 正人 川口 亮平 Surono Muhamad Hendrasto Umar Rosadi

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 2010 (ISSN:24335320)

巻号頁・発行日

pp.26, 2010-10-09 (Released:2017-02-10)

著者

鹿野 和彦 金子 信行 千葉 とき子

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 2014 (ISSN:24335320)

巻号頁・発行日

pp.69, 2014-11-02 (Released:2017-02-10)

著者

小林 哲夫 岩元 洋一 奥野 充

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 2004 (ISSN:24335320)

巻号頁・発行日

pp.26, 2004-10-19 (Released:2017-02-10)

著者

阪口 圭一 小林 哲夫

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.1989, 1989

被引用文献数

1

著者

三村 弘二 金谷 弘

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.46, no.1, pp.17-20, 2001

参考文献数

11

被引用文献数

2

著者

齋藤 政城 松島 健 松尾 〓道 清水 洋

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.2006, 2006

著者

鹿野 和彦 大口 健志 林 信太郎 宇都 浩三 檀原 徹

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.373-396, 2002

参考文献数

82

被引用文献数

3

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An alkali-rhyolite tuff-ring is newly identified in the western end of the Oga Peninsula and named as Toga volcano in this paper. The existence of this maar-type volcano at the Toga Bay has been suspected for a long time because of the elliptical embayment reminiscent of a maar and the distribution of the Toga Pumice localized along the bay coast. The Toga Pumice is cornposed mainly of pumice and non- to poorly-vesicular glass shards, but many pumices of lapilli size are rounded and fines are poor giving a sandy epiclastic appearance to the deposit. In our latest survey along the bay coast, the Toga Pumice is found to be in direct contact with the basement rocks. The contact steeply inclines at 40-50° and envelopes an elliptical area 2.0 km×2.4 km covering the bay and bay coast to form a funnel-shape structure. The basement rocks at the contact are brecciated to a depth of several tens of centimeters, or collapsed into fragments to be contained in the Toga Pumice. The beds inside the inferred crater incline toward the center of the crater at 10-30° or much smaller angles, presumably reflecting a shallow concave structure infilling the more steeply sided crater. The deposit is thinly to thickly bedded to be parallel- to wavy- or cross-stratified, inversely to normally graded with many furrows, rip-up clasts and load casts, and is sorted as well as fines-depleted pyroclastic flow deposits and/or pyroclastic surge deposits. These features are characterisitic to turbidites and indicate the place of emplacement was filled with water. Constituent glass shards are, however, commonly platy or blocky and likely to be phreatomagmatic in origin, and pumice lapilli are interpreted to have been originally angular but rounded by repeated entrainment and abrasion in multiple phreatomagmatic eruptions and succeeding emplacement in the crater lake. A pyroclastic surge deposit (Oga Pumice Tuff) correlative in composition and age to the Toga Pumice occurs at Anden and Wakimoto, 11 km and 15 km east of Toga, respectively. The juvenile pumice lapilli are angular to subrounded, in contrast with the pumice lapilli of the Toga Pumice.

著者

下司 信夫

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.1999, 1999

著者

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:04534360)

巻号頁・発行日

vol.23, no.2, pp.117-130, 1978

被引用文献数

1

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約半世紀にわたる実験岩石学的研究により,主要なマグプの生成に関する物理化学的条件については,かなり解明されたと言ってもよいであろう. しかし,マグマ生成の物理化学的条件が分っただけではマグマの成因を理解したことにはならない. マグマカミ生成し,地表あるいは地殻浅部に到達するまでのメカニズムを理解して,はじめてマグマの成因が分ったと言える. このためにも,マグマの物理的性質についての知識は重要である. 本稿では,マグマの物理的性質のうち,移動現象に関係のある粘性と密度とをとりあげる.