20 0 0 0 OA 福島県南部,二岐山火山の噴火史とマグマ供給系
- 著者
- 渡部 将太 長谷川 健 小畑 直也 豊田 新 今山 武志
- 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.129, no.1, pp.307-324, 2023-04-06 (Released:2023-04-06)
- 参考文献数
- 64
二岐山火山の活動は,溶岩流ステージと溶岩ドームステージに大別される.溶岩流ステージの活動は,約16~9万年前には東~南~西部へ主に溶岩流を繰り返し流出し(合計1.57 km3 DRE),約9~8万年前には北部に大規模な溶岩流を流出した(合計約1.99 km3 DRE).その後の溶岩ドームステージ(約9~5万年前の間)では山体中央部に小規模な溶岩ドームを形成した(合計約0.09 km3 DRE).噴出率は約16~9万年前で低く,約9~8万年前で最大となり,それ以降は低くなる.本火山では珪長質マグマと苦鉄質マグマの混合が支配的である.溶岩流ステージと溶岩ドームステージとの間でマグマの化学組成が明瞭に変化し,異なる2つの混合トレンドが認められる.両ステージ間の苦鉄質マグマの化学組成の違いはかんらん石と輝石の分別で,珪長質マグマの化学組成の違いは,同一の地殻物質の部分溶融度の違いでそれぞれ説明可能である.
13 0 0 0 OA 多量の漂流軽石を発生させる噴火—南西諸島における軽石の漂着記録とその給源火山の活動から
- 著者
- 及川 輝樹 池上 郁彦 渡部 将太
- 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.68, no.3, pp.171-187, 2023-09-30 (Released:2023-11-02)
- 参考文献数
- 73
Submarine volcanic eruptions produce a large amount of drifting pumice around the globe at a frequency of once every several to ten years. However, there is little knowledge about what kind of eruptions produce them. Document records of large amounts of pumice washed ashore in the Nansei Islands in southwest Japan are summarized in this article, along with an assessment of their source volcanoes and eruption frequency and style. A large amount of drifting pumice has washed ashore on the Nansei Islands eight times (1778 or 1779, 1905, 1914, 1915, 1924, 1934, 1986, 2021) since the 18th century, seven of which were after the 20th century, at a frequency of several times every 100 years. This frequency is not remarkably low compared to other natural hazard events. The eruptions that provided the source of these drifting pumice were the Fukutoku-Oka-no-Ba 1904‒1905 and 1914 eruptions, the Myojin-Shou 1915 eruption, Submarine Volcano NNE of Iriomotejima 1924 eruption, the Showa Iwo-jima 1934 eruption and the Fukutoku-Oka-no-Ba 1986 and 2021 eruptions. In the 8 recorded volcanic eruptions, including the uncertain ones, 6 were due to submarine volcanic eruptions in the southern part of the Izu-Bonin Arc. It took 2 to 6 months (mostly 2 to 4 months) for drifting pumice to reach the shores of the Nansei Islands from the Izu-Bonin Arc. The eruption styles that generated a large amount of drifting pumice can be divided into three cases. (1) An eruption that ejects a large amount of pumice from the seafloor to the sea surface and causes a steam-based volcanic plume to rise at the center of the eruption. They often occur from vents with seafloor depths of several hundred meters (Submarine Volcano NNE of Iriomotejima 1924 and Showa Iwo-jima 1934), but they also occur in shallower waters (Myojin-Shou 1915). (2) An eruption that occurs in shallow water (<50 m), with repetitive Surtseyan eruption activity that forms islands composed of large amounts of pyroclastic material, while at the same time producing large amounts of drifting pumice (Fukutoku-Oka-no-Ba 1904‒1905, 1914 and 1986). (3) An eruption that occurs in shallow water (<50 m) and produces a volcanic plume reaching the stratosphere. This style of eruption forms an island and generates a large amount of pyroclastic material, including drifting pumice (Fukutoku-Oka-no-Ba 2021).
- 著者
- 山本 啓介 城戸口 和希 鈴木 大河 小荒井 衛 今泉 利架 杉野 伊吹 遠藤 史隆 大友 眞太郎 小関 敏史 柴田 翔平 菅原 慎吾 渡部 将太
- 出版者
- 一般社団法人 日本地質学会
- 雑誌
- 日本地質学会学術大会講演要旨 (ISSN:13483935)
- 巻号頁・発行日
- vol.2017, 2017