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

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

被引用文献数

3

---

The 1914-1915 Sakurajima eruption was the largest eruption in Japan in the 20th century and erupted andesitic magma was about 1.5km^3 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

安井 真也 高橋 正樹 島田 純 味喜 大介 石原 和弘

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.58, no.1, pp.59-76, 2013-03-29

被引用文献数

1

---

桜島火山の歴史時代の大規模噴火である安永噴火(1779-1782年)と大正噴火(1914-1915年)の噴出物の岩相や層序,地形,噴火当時の記録を比較した.両噴火では山頂をはさんだ両測山腹で割れ目火口列が活動した.割れ目の推定の長さは大正噴火で約2.3km,安永噴火では5kmに及ぶ.噴火開始後数10時間の大正噴火と安永噴火の噴火様式は共通しており,プリニー式噴煙柱から火口近傍への大量の火砕物降下により斜面上に火砕丘を形成しながら火砕成溶岩をもたらした.引き続く数週間には両噴火とも溶岩流出が繰返されて溶岩原が形成された.その後は,大正噴火が陸上での溶岩流出を主としたのに対し,安永噴火では北東沖で海底噴火が起きて安永諸島を形成した点で大きく異なる.両噴火とも噴火初期に割れ目火口近傍へ著しい火砕物降下があることが特徴的である.これは火山体形成の観点からは,両噴火では山頂部の地形変化はほどんどないが,山腹斜面が成長したことを意味する.また桜島の大規模噴火の減災という観点では,居住地域近くまで到達しうる割れ目火口の活動への迅速な初期対応の重要性を示している.

著者

Sri HIDAYATI 石原 和弘 井口 正人

出版者

The Volcanological Society of Japan

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.52, no.6, pp.289-309, 2007-12-28 (Released:2017-03-20)

参考文献数

41

被引用文献数

11

---

山頂噴火活動が低下し,姶良カルデラの地盤が膨張に転じた1993年以降,桜島とその周辺では火山構造性地震の発生頻度が漸次高まった.2003年11月からは桜島南西沖の6〜9kmの深さで地震が多発し,従来ほとんど発生が認められなかった姶良カルデラ北東部でも地震が発生した.翌年末にはGPSによりカルデラの地盤の膨張が観測されたが桜島の噴火活動に顕著な変化はこれまでのところ認められていない.1998~2005年に発生した火山構造性地震の震源と発震機構を求め,火山活動およびマグマ供給系との関係を検討した.(1)桜島およびその周辺の火山構造性地震の震源は姶良カルデラから桜島を通ってその南西側にかけて分布し,これらは,桜島南岳直下の深さ0〜4km,南西沖深さ6〜9kmおよび姶良カルデラ内深さ4〜14kmの3つの領域に分けられる.南岳下の深さ2kmまでの発震機構は逆断層型が卓越するが,2kmより深い部分では横ずれ型が卓越する.(2)桜島南西沖の火山構造性地震は張力軸が西北西-東南東方向の正断層型であり,(3)姶良カルデラ内の火山構造性地震の節面の方向は構造線の方向に〜致しており,いずれもこの地域のテクトニクス場と調和的である.(4)桜島南西沖の地震活動が姶良カルデラから桜島を横切るマグマの貫入イベントに関連しているのではないかという仮説にたって,地殻変動データを吟味してその可能性を検討するとともに,新たなマグマ供給系モデルを提示した.

著者

石原 和弘 為栗 健 井口 正人

出版者

京都大学防災研究所

雑誌

学士会会報 (ISSN:0386412X)

巻号頁・発行日

vol.2014, no.3, pp.61-65, 2014-05

著者

井口 正人 石原 和弘 高山 鉄朗 スアンティカ グデ チェチェップ ウィンピー スクヒャール ラデン スタウィジャジャ イガン スガンダ オニー

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報 (ISSN:0386412X)

巻号頁・発行日

no.39, pp.161-171, 1996-04

著者

綿貫 陽子 鎌田 浩毅 味喜 大介 石原 和弘

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.48, no.6, pp.513-518, 2003

参考文献数

16

被引用文献数

1

---

During the Taisho Eruption (1914-1915) of Sakurajima Volcano, the Secondary Lava Flows drained out from the front of the primary lava flows after a certain pause from their settlement. We investigate distribution, timing and conditions of the effusion of the Secondary Lava Flows which have not been clarified yet. We define the features of the Secondary Lava Flows by means of geomorphological interpretation using aerial photographs and field survey. More than 200 landscape photographs, which were taken at the time of the Taisho Eruption, indicate that the earliest Secondary Lava Flows effused on 14 February 1914; this date was several months earlier than those previously considered. The effusing of the Secondary Lava Flows did not occur as a single event but as several events in different areas. Based on volumetric estimation of the individual Secondary Lava Flows, the volume of the Secondary Lava Flows tend to have increased as time passed after the eruption. The Secondary Lava Flows effused from the underlying tip of river valleys.

著者

石原 和弘

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報 (ISSN:0386412X)

巻号頁・発行日

no.55, pp.107-115, 2011

著者

安井 真也 高橋 正樹 石原 和弘

出版者

日本大学文理学部自然科学研究所

雑誌

日本大学文理学部自然科学研究所研究紀要 地球システム科学 (ISSN:13432745)

巻号頁・発行日

no.41, pp.75-107, 2006

著者

周藤 正史 宇都 浩三 味喜 大介 石原 和弘 巽 好幸

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B (ISSN:0386412X)

巻号頁・発行日

vol.43, no.B-1, pp.15-35, 2000-04-01

---

姶良カルデラにおいて2万5千年前に起こった, 爆発的な姶良火砕噴火に至るまでの火山活動をK‐Ar年代測定法により調べた。姶良カルデラ縁に分布する火山岩32試料のK-Ar年代値によると, (1)3‐lMaにカルデラ南北縁で安山岩質, (2)1‐0.4Maに北西縁で玄武岩‐流紋岩質, (3)0.4‐0.1Maに南西縁で玄武岩‐流紋岩質, (4)0.1‐0.025Maに北縁で安山岩質, 及び南北線でほぼ同時期に流紋岩質の活動が起こった。姶良カルデラ直下において現在存在が推定される流紋岩質マグマ溜まりは(4)の時期には既に存在していたのかもしれない。キーワード:姶良カルデラ, K。Ar年代測定, 火山活動史, 爆発的噴火, マグマ溜まり

著者

木股 文昭 石原 和弘 植木 貞人 内田 和也 小山 悦郎 佐藤 峰司 鈴木 敦生 高山 鐵朗 竹田 豊太郎 辻 浩 寺田 暁彦 中坊 真 浜ロ 博之 平野 舟一郎 松島 健 宮島 力雄 森 済 八木原 寛 山本 圭吾 渡辺 秀文

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報 (ISSN:0386412X)

巻号頁・発行日

vol.42, no.1, pp.35-43, 1999-04

---

1998年以降, 火山活動が活発化している岩手山火山において, 火山活動に伴う地殻上下変動とその圧力源を議論する目的で, 水準路線を設置し, 1998年7, 9, 11月に精密水準測量を実施した。1998年9月3日, 水準測量実施中に, 直下でM6.1の地震が発生し, 20cmに達する断層運動を水準測量で検出した。岩手山南麓ではこの4ヶ, 月間に4cmに達する山側隆起の上下変動が観測され, その圧力源は岩手山西方に深さ3km前後と推定される。Earthquake swarm is observed around the Iwate-san Volcano, Northeast Japan since 1998. The leveling route with distance of 36 km was set up around the volcano and the precise levelings have been repeated to discuss the crustal deformation four times in July, September, September and November in 1998. When the precise levelingis doing in September 3, 1998, earthquake of M6. 1 was occurred close to the volcano. One leveling team was making leveling in the epicenter area, Re-levelings were repeated since the next day of the earthquake, and coseisimic deformations of 20 cm are detected along the leveling route. However the precursor of the vertical movements is not recognized in the leveling data made just before the earthquake. Uplift of the Iwate-san Volcano is observed and which amounts to 4 cm in the period of July to November in 1998. The pressure sources of the vertical deformations are estimated to be under the west side of the volcano with depth of 3 kim, which is the almost the same location of the pressure estimated by GPS measurements and the DInSAR (Differential Interferometric SAR).

著者

西 潔 石原 和弘

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.48, no.5, pp.407-413, 2003-11-06

参考文献数

11

---

A new scheme for hypocenter calculation is proposed for volcanic regions. The scheme finds the global minimum of the travel time residual, and the resulting solution is more stable than that from the conventional Geiger's method, especially when the number of observations is small or the station distribution is unsuited. In the first step (Step 1) of this scheme, the target area js parameterized by the node. The node distance depends on the heterogeneity of the velocity structure; usually about 0.3-1 km is sufficient. Travel times between nodes and stations are stored. In the first half of the second step (Step 2A), a node is sought that minimizes the sum of squares of the travel time residuals for the event. By changing the depth of this node, a set of initial hypocenter candidates is generated. In the following step (Step 2B), with these candidates for the initial hypocenter, precise locations of the event are obtained by nonlinear calculations using the simplex method. The hypocenter with minimum travel time residual is then selected as the most probable hypocenter. For the travel time calculation, the 3-D robust seismic ray tracer known as Fermat (Nishi, 2001) is used. If the velocity structure and the locations of the observation stations do not change, the results of Step 1 are effective for all events. Consequently, repetitions of only Step 2A and 2B are sufficient for every event. Successful outcomes of calculation using synthetic and actual data are obtained with practicable CPU times.

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

---

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

周藤 正史 宇都 浩三 味喜 大介 石原 和弘

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.2001, no.2, 2001-10-01

著者

井口 正人 石原 和弘

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報 (ISSN:0386412X)

巻号頁・発行日

no.33, pp.p1-12, 1990-04

被引用文献数

5