著者

下司 信夫 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.51, no.1, pp.1-20, 2006-02-28

被引用文献数

2

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Volcanic history of Kuchinoerabujima Volcano in the last 30,000 years is reconstructed based on tephra stratigraphy. Kuchinoerabujima is a volcanic island which is a cluster of at least nine volcanic edifices; Gokyo, Jyogahana, Ban-yagamine, Takadomori, Noike, Kashimine, Hachikubo, Furutake and Shintake. Eruptions within the last 30,000 years occurred from Noike, Hachikubo, Furutake and Shintake volcanoes. Two major pumice and scoria eruptions occurred between 15 and 11 ka after an inactive period since ca. 30ka. NoikeYumugi tephra (15-14ka, DRE>0.06km^3), erupted from the summit of Noike Volcano, consists of Yumugi pumice fall deposit and Nemachi pyroclastic flow deposit. Furutake-Megasaki tephra (12-11 ka, DRE ca. 0.8km^3) erupted from Furutake Volcano and consists of Furutake agglutinate, Furutake scoria flow deposit and Megasaki scoria fall deposits. Volcanic edifice of Older Furutake was built during the 12-11 ka eruption. Eruption style changed around 10ka, after the collapse of Older Furutake Volcano. Activities of Yougner Furutake and Shintake Volcanoes are characterized with effusion of lava flow and no major pumice eruption is recognized. Lithic tephra erupted from Younger Furutake and Shitake Volcanoes within the last 10,000 indicates repetitive Vulcanian-type and phreatomagmatic eruptions. All historical eruptions since 1841 occurred at and around Shintake crater and were Vulcanian-type explosions with emission of magmatic materials and phreatic explosions.

著者

須藤 靖明 筒井 智樹 中坊 真 吉川 美由紀 吉川 慎 井上 寛之

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.51, no.5, pp.291-309, 2006-10-31

被引用文献数

5

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So far the ground deformation associated with a magma supply system of Aso Volcano had not been discussed because any clear signals in ground deformations and volcanic earthquake activity had been hardly observed near the Nakadake active crater during its activity enhancement cycles. In this article, however, the deflation source and magma supply system is investigated by the long-term geodetic surveys. The secular subsidence is observed in the Kusasenri area about 3km west of the Nakadake active crater from the 1951's levelling survey in compiled levelling surveys along the Bouchuu-line since 1937. While the ground deformation near the active crater has been obscure. The source of this deflation near the Kusasenri area is estimated on the basis of the spherical pressure source model through the non-linear least square method with using recent survey data which include the Bouchuu-line and an extended survey route. The deflation source is located beneath the Kusasenri area at about 5km depth. However, recent volume changes at the spherical deflation source are smaller than before 1959. The location of the deflation source coincides with the low P- and S-wave velocity body in the 3D seismic velocity structure. This fact supports a hypothesis that the low seismic wave velocity body represents a magma reservoir. Therefore this magma reservoir beneath the Kusasenri area must be connected to the Nakadake active crater. We inferred a rigid conduit in the magma supply system from the obscure ground deformation in the vicinity of the Nakadake crater.

著者

小山 真人

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.1995, no.2, 1995-10-03

著者

町田 洋 新井 房夫 百瀬 貢

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, no.2, pp.49-70, 1985-07-01

被引用文献数

41

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The Aso-4 pyroclastic flow is one of the largest of late Pleistocene age in Japan covering extensive areas of Kyushu around the Aso caldera and western part of Honshu. We have recently discovered a distal ash which has very similar petrographic and chemical properties to the flow deposits at several localities of Japan, and is assumed to be an airfall part of the Aso-4 unit. The ash, named the Aso-4 ash, is a crystal-vitric fine-grained ash, consisting of rhyodacitic bubble-walled glass shards, and brown hornblende and orthopyroxene (bronzite) as mafic phenocrysts. Its identification is carried out by combined parameters ; refractive index of glass ranges 1.506-1.511, low refractive index of orthopyroxene (γ=1.699-1.701) and relatively high index of hornblende (n_2=1.687-1.688). In addition glass in the ash is characteristically rich in potassium. These properties are similar to those of the Aso-4 pyroclastic flows. It is suggested that the ash is a coignimbrite airfall deposit of fine-grained materials from the upper part of an eruption column formed at the same time as the Aso-4 flow. The ash mantles extensive areas from Kyushu to Hokkaido and is also recognized and identified in several piston cores from the Sea of Japan and the northwest Pacific Ocean. The fallout area of this ash is now known to attain approximately 4×10^6 km^2. It is striking that in the eastern part of Hokkaido, ca. 1700 km distant from the source, the ash with the thickness of 15 cm is well preserved immediately below the Kutcharo pyroclasitc flow deposits II/III. The bulk volume of this ash is estimated to be more than 400 km^3, possibly larger than that of the flow deposits. The stratigraphic position of this ash in standard sequence of South Kanto shows that it occurs after the Obaradai interstade (ca. 80 ka) and before the Misaki interstade (ca. 60 ka). Thus the Aso-4 ash provides a very important datum plane in late Pleistocene sequence in and around Japan.

著者

岡田 肇 横山 勝三

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.27, no.1, pp.67-69, 1982-04-30

著者

金子 克哉 伊藤 公一 安部 祐一

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.55, no.2, pp.109-118, 2010-04-30

参考文献数

10

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Monitoring of volcanic phenomena close to active volcanic vents and inside active craters is needed to predict change of volcanic activities and to understand dynamics of volcanic eruptions. In order to carry out safe volcanic monitoring, we have developed a prototype of a mobile sensor for volcanic observation "HOMURA" which is a new robotic system that has been designed to observe volcanic phenomena inside active volcanic craters. HOMURA is a small unmanned ground vehicle (approx. 780×560×300mm in dimension and 10kg in weight) with six wheels driven by electric motors and it is operated by wireless remote control at a distance of more than 1km. Data measured by some sensors in HOMURA are sent to the base station in real time. Materials of the vehicle body and wheels are aluminum with 2mm thick and plywood with 9mm thick, respectively. HOMURA can climb up and down a rough surface with slope angle of 30 degree. In addition, HOMURA does not readily become undrivable even in overturning during climbing because it has a unique body shape with a horizontal symmetry plane. HOMURA can be made and transported to mission fields at small costs. These allow us to make a new vehicle even if HOMURA should be lost by accident during missions and promptly to explore a sudden volcanic event by HOMURA. In test campaigns at Aso volcano and Izu-Oshima volcano, we confirmed that HOMURA has planned abilities on moving on rough surfaces and wireless communication.

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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.26, no.2, 1981-07-01

著者

早川 由紀夫 小山 真人

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.43, no.5, pp.403-407, 1998-10-30

被引用文献数

14 12

著者

及川 輝樹

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

巻号頁・発行日

vol.2012, 2012-10-14

著者

石原 和弘 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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.33, no.3, pp.269-271, 1988-10-31

被引用文献数

2

著者

伊藤 英之 林 信太郎 三浦 光世 内柴 良和

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, 2006-10-23

著者

平林 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.33, no.2, pp.p102-104, 1988-07

著者

山科 健一郎

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.43, no.5, pp.385-401, 1998-10-30

被引用文献数

2

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Various suggestive documents and associated sketehes are collected for understanding the pre-eruptive and the earliest stages of the 1914 great eruption of Sakurajima volcano, southwestern Japan, in Taisho era. Based on these records, the premonitory process to the eruption was reviewed especially with respect to the occurrence of many earthquakes which resulted in repeated rock falls with dust clouds, unusual upwelling of water and hot spring, and emission of volcanic smoke in the morning of January 12. Although there are many descriptions on the beginning of the remarkable eruption, they are sometimes inconsistent with each other. In the present paper, it is proposed that the valcano started to erupt around 09 : 58 on January 12 (Japanese Standard Time) at 200 m in height in the western slope of the mountain. In several minutes, a line of craterlets was formed between 200-500 m in height in the WNW-ESE direction. The development of a subsurface fissure in this direction resulted in another outbreak in the southeastern slope probably around 10 : 05. For the better understanding of this important eruptive event, discoveries of additional references are still desired.

著者

小林 哲夫 早川 由紀夫 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.28, no.2, pp.129-139, 1983-07-01

被引用文献数

6

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大隅降下軽石堆積物は, 約22, 000年前に鹿児島湾最奥部で起こった一連の巨大噴火の最初期のプリニアン噴火の産物である.灰白色の軽石と遊離結晶および少量の石質岩片からなる本堆積物は, 全層にわたってほぼ均質な見かけを呈するが, 多くの場合, 上方に向かって粒径がやや大きくなる逆級化層理を示す.層厚分布図(Fig.3)と3種の粒径分布図(軽石の平均最大粒径・石質岩片の平均最大粒径・堆積物の中央粒径;Figs.5, 6, 7)は, いずれも本堆積物の噴出火口が姶良カルデラの南縁, 現在桜島火山の位置する地点付近にあったことを示している.分布軸は火口からN120°E方向に伸びるが, 分布軸から60 km以上離れた地点にも厚く堆積している.又, 堆積物は分布軸の逆方向すなわち風上側にも20 km以上追跡できる.分布軸上で火口から30 km離れた地点での層厚は10 mに達するが, 40 km地点より遠方は海域のため層厚値は得られない.そのため噴出量の見積もりには多くの困難が伴うが, すでに知られている他のプリニアン軽石堆積物の層厚-面積曲線(Fig.4)にあてはめて計算すると, 総体積98 km^3(総重量7×10^<16>g)が得られ, 本堆積物は支笏-1軽石堆積物(116 km^3)に次ぐ最大規模のプリニアン軽石堆積物であることがわかる.3種の粒径分布図から得られる粒径-面積曲線(Fig.8)は, 噴出速度・噴煙柱の高さ・噴出率などで示される噴火の「強さ」を比較する上で有効である.それにより, 大隅降下軽石噴火の「強さ」はけっして例外的なものではなく, プリニアン噴火の平均あるいはそれをやや上回る程度であったことが判明した.

著者

杉浦 孜 杉崎 隆一 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.4, pp.231-244, 1980-12-01

被引用文献数

2

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Ontake Volcano suddenly began to erupt on its south-western flank near the summit at 05^h20^m on Oct, 28, 1979, forming several new craters and ejecting large amounts of volcanic ash and steam. Up to that time, the volcano had been believed to be dormant, though there were weak geothermal activities at a part of the south-western flank of the volcano, Jigokudani. This paper reports some results obtained by preliminary examination of volcanic ashes, thermal waters and gases collected on and around Ontake Volcano during the early stage of eruptive activity. The volcanic ashes are homogeneous in chemical and mineralogical compositions, and similar in chemical composition to the pre-historic volcanic ashes. The ashes contain pyrite, anhydrite, cristobalite and clay minerals. The sulfur isotopic equilibrium temperature is estimated to be about 400℃ for pyrite-anhydrite pairs in the volcanic ashes. The estimated temperature is apparently too high for the temperature of phreatic explosion. The interpretation of this isotopic data remains unsettled. The thermal waters collected from the boiling pools in craters are enriched in D and 19^<O>. The isotopic enrichment is probably caused by evaporation of water at the surface of boiling pool. The hydrogen and oxygen isotopic data also suggest that spring waters issuing around Ontake Volcano are meteoric in origin. Nigorigo Hot Spring, about 4 km north-west of Ontake Volcano, showed significant increases in the concentrations of major dissolved chemical components soon after the eruption, but since then no significant change in chemical and isotopic composition has been observed

著者

神沼 克伊 桜井 治男 馬場 めぐみ 中田 まゆみ

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.4, pp.313-314, 1980-12-01

著者

小山 真人 吉田 浩

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.177-190, 1994-09-20

被引用文献数

9

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A magma-discharge stepdiagram, which shows a relationship between time and cumulative discharge volume/mass of a volcano, is a useful tool for estimating a magma supply/discharge system beneath the volcano. We propose a model to explain the shape of the magma-discharge stepdiagram, and estimate effects of an abrupt change in crustal stress/strain field, which can modulate the shape of the stepdiagram. Using the shape of the stepdiagram, volcanoes can be classified into four types : time-predictable (TP), volume-predictable (VP), strictly-periodic (SP), and nonpredictable (NP) volcanoes. In the TP volcano, the length of a dormant period is proportional to the magma-discharge volume of the preceded eruption. In the VP volcano, the discharge volume of an eruption is proportional to the length of the preceded dormancy. In the SP volcano, both a length of a dormant period and a discharge volume of an eruption do not change. In the NP volcano, both a length of a dormant period and a discharge volume of an eruption do not have clear predictability. The predictability in the TP, VP, and SP volcanoes can be explained using a simple magma supply/discharge model beneath a volcano, assuming that ascent pressure at the top of a magma reservoir (P_m) monotonously increases in a dormant period, and that magma-discharge volume is proportional to the decrease of P_m at an eruption. Besides these two assumptions, the TP and VP volcanoes need a constant upper limit (P_u) and a constant lower limit (P_l) of P_m, respectively. The SP volcano needs constant P_u and P_l. The magma-discharge stepdiagrams of the TP, VP, and SP volcanoes can be modified by a large intrusive event, changes of physico-chemical parameters in a magma reservoir, a magma-supply rate from the lower crust or mantle, structural evolution of a magma-supply/discharge system, a small eruption which does not affect the predictability of a magma-discharge stepdiagram, and an abrupt change in a crustal stress/strain field. Such modifications spoil the predictability in the stepdiagrams and thus make the NP volcano. An abrupt change in a crustal stress/strain field causes a change in P_m and/or P_u and thus can modify a magma-discharge stepdiagram. Particularly, an increase in P_m and/or a decrease in P_u can trigger an eruption. An upward shift of a magma-discharge stepdiagram may be a key to finding such a trigger of an eruption and to estimating mechanisms of triggering.

著者

久保寺 章

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.26, no.4, 1981-12-28

著者

上野 龍之

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.533-544, 2016-09-30 (Released:2016-11-08)

参考文献数

26

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The Tsumaya pyroclastic flow deposit is one of the main units of the Aira pyroclastic eruption, which produced the Aira caldera in Southern Kyushu, Japan, 30,000 years ago. The Tsumaya deposit overlies the main plinian unit, the Osumi pumice fall deposit, and is covered by the large-volume pyroclastic flow unit, the Ito pyroclastic flow deposit. The Tsumaya deposit consists of massive facies associated with smaller volume of stratified facies. The total eruption mass is 2.8×1013 kg (estimated by the crystal method), of which approximately 48 % was elutriated to a co-ignimbrite ash fall. The upper part of the Osumi pumice fall deposit is intercalated with the stratified facies of the Tsumaya pyroclastic flow deposit, indicating that the Tsumaya eruption began during the final phase of the Osumi eruption. The Tarumizu pyroclastic flow and the Osumi pumice fall were produced from the same vent in the southern part of the caldera. The Tsumaya pyroclastic flow deposit has been considered to be the same stratigraphic unit as the Tarumizu deposit;however, the two deposits have contrasting origins and different contents of lithic fragments, indicating they were erupted from different vents. Lateral variations in the altitudes of the depositional surface of the Tsumaya deposit indicate that the Tsumaya pyroclastic flow was erupted from the northeastern part of the Aira caldera.