著者
三宅 康幸 小坂 丈予
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.113-121, 1998-06-10 (Released:2017-03-20)
参考文献数
14
被引用文献数
2

A steam explosion occurred at about 14:30 JST, February 11th, 1995, in the hot-spring area near Yakedake volcano, central Japan. More than six workers were near the site of the explosion for the road construction, and four of them were buried by the ejected material and killed. A small initial explosion began at the bottom of a 4m deep moat dug by a backhoe and it was followed by the maximum explosion, which ejected about 6,000m3 of blocks (maximum length is more than 2m) and mud, with steam and volcanic gas. The ejecta contain gravels of welded tuff, granite and mesozoic sedimentary rocks, which are the components of a pyroclastic dike of Pliocene age, and pumiceous lapilli tuff derived from the terrace sediments covering the pyroclastic dike. The explosion caused a landslide from the western cliff and the vent was buried by the slid debris, most of which was blown away by the second explosion. All of these processes took place within a few minutes. A small depression (20×5m2) on the west of the mound of the ejecta may represent part of the vent; its depth is estimated to be about 60m or more. Gaseous S02(<30ppm) and H2S(<90ppm) were detected at the explosion site for three days after the explosion. The chemical composition of gas collected from the holes drilled after the explosion were nearly same as the gas from the summit crater of the Yakedake volcano. Because a wall-like Low-Q zone is suggested by seismologists beneath Yakedake volcano and the explosion site, it is most probable that there existed a magma beneath the explosion site and that the heat for the explosion was supplied by the magma and gas exsolved from the magma.
著者
伊藤 英之 脇山 勘治 三宅 康幸 林 信太郎 古川 治郎 井上 昭二
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.50, no.6, pp.427-440, 2005
参考文献数
27

The Yakedake volcano is located in the southern part of the northern Japan Alps, central Japan. Yakedake volcanic hazard map was published in March 2002, and in June 2002, it was distributed to the inhabitants of Kamitakara village, Gifu prefecture, where is located 4-20km west from the volcano. In January 2003, the questionnaire survey was carried out on the inhabitants in order to know their attitudes to the volcanic hazard map and the level of their understanding of the contents of the hazard map. The Kamitakara village office distributed the questionnaires to 1,102 families through the headman of each ward, the headman collected 802 answers. The results of analysis were as follows. 89% of the respondents knew the existence of the hazard map and 35% read it well, but about 11% have not read the map at all. The elders have a tendency to have deeper understanding of the hazard map than younger ones, especially in elders who have experiences to meet some kinds of natural hazards. And the people who once attended the explanatory meeting of the hazard map, which was held for the residents living inside the disaster-prone area four times after the publication of the hazard map, also tend to have more proper understandings. The people who are engaged to the tourism give more attention to the volcanic hazard than others. The respondents have strong tendency to require more knowledge about the volcanic activities and hazards. We can say that the further activities by scientists, engineers and administrative officers are expected in order to establish an informed consent, that is, there should be a decision-making by inhabitants themselves and support by officers in charge with detailed explanations.
著者
三宅 康幸 小坂 丈予
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.113-121, 1998-06-10
被引用文献数
4

A steam explosion occurred at about 14:30 JST, February 11th, 1995, in the hot-spring area near Yakedake volcano, central Japan. More than six workers were near the site of the explosion for the road construction, and four of them were buried by the ejected material and killed. A small initial explosion began at the bottom of a 4m deep moat dug by a backhoe and it was followed by the maximum explosion, which ejected about 6,000m^3 of blocks (maximum length is more than 2m) and mud, with steam and volcanic gas. The ejecta contain gravels of welded tuff, granite and mesozoic sedimentary rocks, which are the components of a pyroclastic dike of Pliocene age, and pumiceous lapilli tuff derived from the terrace sediments covering the pyroclastic dike. The explosion caused a landslide from the western cliff and the vent was buried by the slid debris, most of which was blown away by the second explosion. All of these processes took place within a few minutes. A small depression (20×5m^2) on the west of the mound of the ejecta may represent part of the vent; its depth is estimated to be about 60m or more. Gaseous S0_2(<30ppm) and H_2S(<90ppm) were detected at the explosion site for three days after the explosion. The chemical composition of gas collected from the holes drilled after the explosion were nearly same as the gas from the summit crater of the Yakedake volcano. Because a wall-like Low-Q zone is suggested by seismologists beneath Yakedake volcano and the explosion site, it is most probable that there existed a magma beneath the explosion site and that the heat for the explosion was supplied by the magma and gas exsolved from the magma.
著者
津金 達郎 牧野 州明 三宅 康幸 高橋 康
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.49-61, 2006-02-28
被引用文献数
4

The September 2004 eruptions of Asama volcano, central Japan, ejected essential materials such as pumice with bread crust on September 1st and scoria on September 23rd. The textural and chemical analyses on the materials reveal the crystallization processes in a deep magma chamber and a shallow vent. Two distinct stages of crystallization can be recognized in size distributions and morphology of plagioclase phenocryst and microlite both in the pumice and scoria. First stage (range I ): In a deep magma chamber, pyroxene phenocryst began to crystallize out at 1150℃, and then pyroxene and plagioclase continued to nucleate and grow slowly. Second stage (range II) is divided into two sub-stages for pyroxene or three (range IIa-c) for plagioclase. II a: Magma left the chamber and rose slowly through the vent with ever increasing nucleation rate. II b-c: In a shallow vent beneath the crater, numerous plagioclase microlites like swallow-tailed shape precipitated rapidly under a high undercooling condition induced by decompression. Plagioclase microlite in the pumice and scoria developed a characteristic population density like a bell with a peak at the grain size of 0.003mm, which is interpreted to reflect a decrease in nucleation rate of plagioclase, in response to crystallization and establishment of equilibrium during the time duration when the magma stayed in the vent. Magmatic temperatures estimated from plagioclase-glass equilibrium decreased to 850℃ before the September 1st eruption. The similarity in crystal size distribution of the pumice and scoria implies that they had a common ascent history, although groundmass in the scoria has lower crystallinity than that in the pumice, suggesting that the magma of the Sept. 23rd eruption stood lower in the magma column than the Sept. 1st magma.
著者
竹下 欣宏 三宅 康幸 酒井 潤一
出版者
一般社団法人 日本地質学会
雑誌
地質学雑誌 (ISSN:00167630)
巻号頁・発行日
vol.111, no.7, pp.417-433, 2005 (Released:2005-11-01)
参考文献数
60
被引用文献数
7 7 3

古期御岳火山起源のテフラと上総層群中のテフラの対比を角閃石の化学組成値を用いて検討した.その結果,上総層群中の白尾テフラ(BYK)とKs12テフラが古期御岳火山のHサブステージのYUT4もしくは5と溶岩ステージの上浦沢テフラにそれぞれ対比できることが明らかになった.BYKとKs12は内陸地域と海岸地域を結ぶ重要な鍵テフラとなるだけでなく,特にBYKは更新世の前・中期境界の直上に位置するために,中部~関東地方において重要な時間基準面を提供すると考えられる. 上総層群中の9枚のテフラ(Ku6E, Ku5C, BYK, Ka2.4B, Ka2.4A, Ch3, Ch1.5, Ks18, Ks12)に含まれる角閃石の化学組成値はそれぞれ異なることを示した.さらに,黒富士火山,古期御岳火山のテフラも角閃石の組成値により明瞭に区別することができた.それらの結果は,その組成値がテフラの同定,対比の有効な指標になることを示している.
著者
河合 小百合 三宅 康幸
出版者
一般社団法人 日本地質学会
雑誌
地質学雑誌 (ISSN:00167630)
巻号頁・発行日
vol.105, no.9, pp.597-608, 1999-09-15 (Released:2008-04-11)
参考文献数
41
被引用文献数
3 2

最終氷期の指標としての重要性が指摘されている姶良Tnテフラの粒度・鉱物・斜方輝石の化学組成を調べ, それらの地域差をまとめ, 本テフラの運搬・堆積過程を考察した.本テフラのうち最も広域にわたって追跡されるAT 3層・4層は, 噴出源から遠い地点ほど, 粗粒物質の割合・最大頻度粒径・重鉱物含有量・全重鉱物に対する不透明鉱物の割合が, テフラ運搬過程で働く重力淘汰に従って小さくなる.ただし, 大山などの他火山起源のテフラの混入の重鉱物組成への影響があること, 細粒な火山灰ほど, ある距離より遠方では重力淘汰の影響が小さいことなどが指摘される.火山豆石などとして凝集して落下することは, ATの運搬・降下プロセスに大きな影響を与えているとは考えられない.AT 3層と4層は同じ気象条件のもとで問隙をおかず短期間に堆積したと考えられる.
著者
紀岡 秀征 古山 勝彦 三宅 康幸 酒井 潤一 長尾 敬介 池元 壮彦 野入 久幸 小田 貴代美
出版者
The Association for the Geological Collaboration in Japan
雑誌
地球科学 (ISSN:03666611)
巻号頁・発行日
vol.52, no.6, pp.464-474, 1998-11-25 (Released:2017-07-11)
被引用文献数
2

御岳火山中部更新統樽沢累層の溶岩47試料のK-Ar年代を測定した結果,古期御岳火山の火山活動は0.78±0.14 Ma〜0.39±0.006 Maの間である.年代データのそれぞれは,野外で観察された溶岩やテフラの層序関係と調和している.火山活動は,ステージ1(0.78-0.59 Ma)と2(0.53-0.39 Ma)に分けられ,ステージ1はさらに1a(0.78-0.71 Ma),1b(0.71-0.66 Ma)及び1c(0.66-0.59 Ma)に細分される.サブステージ1a,1bには主として玄武岩や安山岩の活動があり,サブステージ1c以降には安山岩やデイサイトが主体となっている.サブステージ1a,1bにはサブステージ1c以降に比べて非常に多くの泥流堆積物が含まれる.この岩相変化は,おそらく火山体の成長と関連している.すなわち,火山成長の初期には,流出した溶岩が各所で流水を堰き止め,できた湖の水とマグマとの相互作用の結果,大量の火山砕屑物が生産された.後には地形の低所は埋め立てられて,さらに粘性の高い溶岩が傾斜の大きな山体を作った結果,火山砕屑物質の生産は終わり,たとえあったにしても急勾配の調査範囲内には堆積しにくくなった.火山体がほぼ円錐状に成長したため,上述した岩相変化のタイミングは円錐火山体の全方向でほぼ一敦する.溶岩に挟在される以下の指標テフラの年代も溶岩の年代から決定できた.それらは,寒原Pm.I:0.70-0.65 Ma,寒原Pm.II:0.67-0.65 Ma,白布沢Pm.:0.61-0.58 Maである.
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

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
竹下 欣宏 三宅 康幸 酒井 潤一
出版者
日本地質学会
雑誌
地質學雜誌 (ISSN:00167630)
巻号頁・発行日
vol.111, no.7, pp.417-433, 2005-07-15
被引用文献数
3 7

古期御岳火山起源のテフラと上総層群中のテフラの対比を角閃石の化学組成値を用いて検討した.その結果, 上総層群中の白尾テフラ(BYK)とKs12テフラが古期御岳火山のHサブステージのYUT4もしくは5と溶岩ステージの上浦沢テフラにそれぞれ対比できることが明らかになった.BYKとKs12は内陸地域と海岸地域を結ぶ重要な鍵テフラとなるだけでなく, 特にBYKは更新世の前・中期境界の直上に位置するために, 中部〜関東地方において重要な時間基準面を提供すると考えられる.上総層群中の9枚のテフラ(Ku6E, Ku5C, BYK, Ka2.4B, Ka2.4A, Ch3, Ch1.5, Ks18, Ks12)に含まれる角閃石の化学組成値はそれぞれ異なることを示した.さらに, 黒富士火山, 古期御岳火山のテフラも角閃石の組成値により明瞭に区別することができた.それらの結果は, その組成値がテフラの同定, 対比の有効な指標になることを示している.
著者
モリス ポール 三宅 康幸 古山 勝彦 ペレス パブロ
出版者
Japan Association of Mineralogical Sciences
雑誌
岩鉱 : 岩石鉱物鉱床学会誌 : journal of mineralogy, petrology and economic geology (ISSN:09149783)
巻号頁・発行日
vol.94, no.11, pp.442-452, 1999-11-05
被引用文献数
4 4

島根県東部中海の若い盾状火山である大根島の玄武岩について全岩の主要元素・微量元素·同位体組成を分析した。K-Ar年代は第四紀の約20万年前の噴出を示している。層準ごとのサンプルの化学組成の変異は,これらがすべて同一の玄武岩質親マグマ(100 Mg/(Mg+Fe)∼56, Ni 101-160 ppm, Cr 110-226 ppm)からの分化物であることを示している。SrとNd同位体組成からは,全地球組成に近い均一な起源物質が示される。初期のマグマは後期よりも低い溶融程度で生じ,より若い溶岩の間の化学的変異は,異なる溶融程度といくらかの地殻物質混合とにより説明される。
著者
公文 富士夫 三宅 康幸 福島 和夫 石田 桂
出版者
信州大学
雑誌
基盤研究(B)
巻号頁・発行日
2006

長野市南部の高野層の補足的なボーリング(約3万~10万年前), 熊本市北部に分布する芳野層のボーリング(37m, 24~36万年前), 長野県川上村の川上湖成層のボーリング(38m, 15~25万年前?)を行った. 高野層については,新規に購入した密度計を利用して粒子密度の解明を行うとともに, 2本目のコア試料の解析によって, 有機炭素含有量等の変動の確認をおこなった. また, 芳野層については有機炭素量測定のほかに, 珪藻や花粉分析によるチェックを行い, 分析はほぼ終了している. 川上湖成層のコア試料については現在解析中である. また, 本研究において気候復元の中心となる有機炭素・窒素量の解析にあたって, 異なる堆積盆間の比較や統合を図るために標準化する手法を導入し, 過去16万年間の連続的な気候変動を明らかにすることができた. この結果に芳野層や川上湖成層の資料を繋ぎ合わせることによって, 過去40万年間の日本列島陸域の気候変動を解明する見通しをえた. また, 海洋および汎世界的な気候変動との正確な対応づけを図るために, JAMSTECによる下北沖コア試料の研究にも参画して, 気候資料を統合して古気候を復元するための準備を進めた.
著者
宇井 忠英 隅田 まり 大学合同観測班地質班 荒牧 重雄 大島 治 鎌田 桂子 小林 武彦 小屋口 剛博 佐藤 博明 中川 光弘 中田 節也 藤井 敏嗣 藤縄 明彦 古山 勝彦 三宅 康幸 横瀬 久芳 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.38, no.2, pp.45-52, 1993-07-01
被引用文献数
2

Small-scale pyroclastic flows due to the collapse of the lava dome have been frequently generated during the 1991-93 eruption of Unzen Volcano. We have recorded video footages which show the generation of pyroclastic flows during January-March 1992. Two types of phenomena have been observed : deformation of the lava dome due to flowage ; and a sudden discharge of gas and ash through fractures and peeling-off of rock fragments from the surface of cooling lava blocks. Pyroclastic flows were generated only in places on the lava dome where these precursory phenomena were frequently observed.