北海道十勝岳火山1926年噴火大正泥流堆積物層序の再検討と古地磁気特性

DOI Web Site 被引用文献1件 参考文献48件
  • 上澤 真平
    日本大学大学院総合基礎科学研究科:(現)北海道大学大学院理学院自然史科学専攻

書誌事項

タイトル別名
  • Restudy of Stratigraphy and Paleomagnetic Characteristics of Taisho Lahar Deposit Associated with the 1926 Eruption on Tokachidake Volcano, Central Hokkaido, Japan
  • ホッカイドウ トカチダケ カザン 1926ネン フンカ タイショウ デイリュウ タイセキブツ ソウジョ ノ サイケントウ ト コチジキ トクセイ
公開日
2008
DOI
  • 10.18940/kazan.53.6_171
公開者
特定非営利活動法人 日本火山学会

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説明

On May 24th 1926, the eruption of Tokachidake volcano, in central Hokkaido, efficiently melted the snow pack on the hill slope, triggering the Taisho lahar which killed 144 people in the towns of Kamifurano and Biei. A geological survey and paleomagnetic and granumetric studies were conducted on the northwestern slope of Tokachidake volcano to reconstruct the sequence of the 1926 eruption and decipher the triggering mechanism for the Taisho lahar. The Taisho lahar deposits in the proximal area of the volcano are divided into five distinct units (unit L1, L2, and A through C, from oldest to youngest). Unit L1 is an older lahar deposit that underlies the 1926 deposits. The 1926 sequence consists of debris avalanche deposits (unit A and C), a laminated sandy debris flow deposit (unit B), and a lahar deposit including scoria clasts (unit L2). Each unit contains hydrothermally altered rocks and clay material with more than 5 wt.% fragments smaller than 2mm in diameter. The progressive thermal demagnetization experiments show that the natural remanent magnetization (NRM) of all samples in unit A, B and C have a stable single or multi-component magnetization. The emplacement temperatures are estimated to be normal temperatures to 620℃ for unit A, 300 to 450℃ for unit B, and normal temperature to 500℃ for unit C. On the basis of geological and paleomagnetic data and old documents, a sequence for the eruption and the mechanism of formation and emplacement of the Taisho lahar can be reconstructed. The first eruption at 12: 11 May 24th triggered a small lahar (unit L2). Collapse of central crater at 16:17 May 24th 1926 then resulted in a debris avalanche containing highly altered hydrothermal rocks with hot temperatures ranging from 300 to 620℃ (unit A). The debris avalanche flowed down the slope of the volcano, bulldozing and trapping snow. Immediately following the collapse, a hot (approximately 400℃) hydrothermal surge (unit B) melted snow and transformed into a lahar causing significant damage and deaths in the towns downstream. Just after the generation of the lahar, another collapse occurred at the crater causing another debris avalanche (unit C).

収録刊行物

  • 火山

    火山 53 (6), 171-191, 2008

    特定非営利活動法人 日本火山学会

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