水蒸気噴火の地質学的研究  [in Japanese] Geological study of phreatic eruptions  [in Japanese]

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Abstract

<p>噴出物中に本質物を含まない水蒸気噴火は,地球上でもっともありふれた噴火の一つである.我々は水蒸気噴火の各種特徴のレビューを行った.水蒸気噴火は,過熱水が急激に水蒸気に変化することで発生する噴火である.水蒸気噴火の噴出物は,粘土分に富んだ火山灰と変質ないし未変質の火山礫・火山岩塊で構成される.一回の水蒸気噴火は1時間から1日程度で終了することが多いが,同程度の規模の噴火を数年間にわたり繰り返すこともある.一回の水蒸気噴火における噴出物量は10<sup>8</sup>m<sup>3</sup>(見かけ体積)以下である.水蒸気噴火で発生する現象は,降下テフラ,投出岩塊,比較的低温(概ね100°C程度)の火砕流,火口噴出型ラハールなどである.このうち低温の火砕流,火口噴出型ラハールの詳しい記載は少ない.層相からそれらの現象を判断し復元できるようにすることは今後の課題である.</p>

<p>Phreatic (non-juvenile) eruptions are the most common type of magmatic activity on Earth. Here we review the characteristics of phreatic eruptions, which occur when overheated water is rapidly vaporized. Tephra layers produced by phreatic eruptions are composed mainly of clay-rich volcanic ash with variably altered lapilli and volcanic blocks. A single phreatic eruption can last between one hour and one day; however, eruptions may occur successively over a period of years to decades. The total volume of tephra produced by a phreatic eruption is typically 10<sup>4-6</sup>m<sup>3</sup>, maximum <10<sup>8</sup> m<sup>3</sup>. Phreatic eruptions may be accompanied by diverse phenomena, including: tephra fallout, ejected rock fragments, low-temperature pyroclastic flows, and syneruptive-spouted type lahars. There are few detailed descriptions of low-temperature (~100°C) pyroclastic flows and syneruptive-spouted type lahars associated with phreatic eruptions. Detailed studies of phreatic phenomena are required, as it remains difficult to identify and reconstruct these processes based on the characteristics of the deposits.</p>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 124(4), 231-250, 2018

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130007413116
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    029098835
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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