阿蘇火山中岳で2003年7月10日と2004年1月14日に起こった湯だまりからの火山灰噴出

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書誌事項

タイトル別名
  • The July 10, 2003 and the January 14, 2004 Ash Emissions from a Hot Water Pool of the Nakadake Crater, Aso Volcano, Japan
  • アソカザン ナカダケ デ 2003ネン 7ガツ 10ニチ ト 2004ネン 1ガツ 14ニチ ニ オコッタ ユ ダ マリ カラ ノ カザンバイ フンシュツ

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説明

Ash emissions occurred from a hot water pool of one of the craters of Nakadake, the only active central cone of Aso Volcano, southwestern Japan, on July 10, 2003 and January 14, 2004. The former ash was dispersed throughout an area extending 14km east-northeast of the vent, whereas the latter ash extended 8km to the east-southeast. Based on isopleth maps, the total weight of ash discharged by each event was 41tons and 32tons, respectively. Both ash-fall deposits were composed of fine-grained (＜1mm) glass shards, crystals and lithic fragments, and contained neither lapilli nor blocks. Some glass shards appear fresh and are probably juvenile material. We therefore believe that these phenomena represent non-explosive gas-and-ash emissions through the hot water pool. The ash particles emitted from the hot water pool of the Nakadake crater were aggregated at a size of 1-3mm and deposited because of a high content of water. The ash-fall deposits in proximal areas (＜1.5km from the crater) were finer grained and more poorly sorted than in distal areas (＞5km). Moreover, the deposit volume obtained from actual data in the proximal area was much larger than the volume extrapolated only from the isopleth data of the distal deposits. These phenomena suggest that the proximal deposits were emplaced mainly by another fine-grain-rich column different from the main ash plume that extended to distal areas, or that some parts of the column detached from the main plume that emplaced the proximal deposits.

収録刊行物

  • 火山

    火山 50 (4), 227-241, 2005

    特定非営利活動法人 日本火山学会

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