桜島火山大正噴火の噴火様式とその時間変化
スポンサーリンク
概要
- 論文の詳細を見る
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.
- 2007-06-29
著者
-
高橋 正樹
日本大文理
-
安井 真也
日本大文理
-
安井 真也
日大文理
-
高橋 正樹
日本大学文理学部地球システム科学科
-
石原 和弘
京都大学防災研究所附属火山活動研究センター
-
味喜 大介
京大・防災研
-
石原 和弘
京大・防災研
-
味喜 大介
京都大学防災研究所
-
味喜 大介
京都大学防災研究所附属火山活勤研究センター
-
安井 真也
日本大学文理学部地球システム科学科
-
石原 和弘
京都大学防災研究所附属火山活勤研究センター
-
高橋 正樹
茨城大学理学部地球生命環境科学科
-
石原 和弘
京都大学防災研究所
-
高橋 正樹
日本大 文理
関連論文
- 浅間山2009年2月2日噴火の噴出物の分布と特徴
- 浅間山2009年2月2日噴火の噴出物の分布と特徴
- 草津白根火山噴出物の全岩主化学組成--分析データ306個の総括
- 丹沢トーナル岩複合岩体中の同時性岩脈と苦鉄質包有岩--産状と全岩希土類元素組成
- 浅間火山1783年噴火と1108年噴火の本質物質の見かけ密度と噴火機構
- 日光男体火山噴出物の全岩化学組成とマグマ供給システム
- 新しい箱根火山像--島弧・島弧衝突境界に噴出した横ずれ活断層に切られた特異な活火山 (総特集 新しい箱根火山像とジオパーク)
- 結晶破砕度からみた溶岩ドーム噴出プロセス--榛名火山・二ツ岳と霧島火山・硫黄山および箱根火山・二子山の比較 (総特集 プロキシマル火山地質学の新展開)
- A32 成層火山を構成する火砕岩の定置機構 : 浅間黒斑火山の例(火山の物質科学(3),日本火山学会2008年秋季大会)
- A27 富士火山青木ヶ原玄武岩質溶岩の斑晶斜長石について(火山の物質科学(2),日本火山学会2008年秋季大会)