カルデラ生成噴火の準備過程解明に向けた研究の展望  [in Japanese] Future view to understanding the preparation process of caldera forming eruptions  [in Japanese]

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Author(s)

    • 鍵山 恒臣 Kagiyama Tsuneomi
    • 京都大学理学研究科地球熱学研究施設火山研究センター Aso Volcanological Laboratory, Graduate School of Science, Kyoto University

Abstract

本論文は,カルデラ生成噴火の準備過程がどのように進行しているかを研究するために下記の仮説を提案する.火山活動には2つの端的な例に代表される多様性がある.この多様性は,マグマが地表に噴出しやすいか,地下に滞留しやすいかによって規定されており,噴出が容易な場合には噴火卓越型火山活動,滞留が容易な場合には地熱活動卓越型火山活動となる.マグマが地下に容易に滞留できる条件下では,間欠的に深部から供給されるマグマは,地表に達することなく地下に滞留するイベントを繰り返す.地下に滞留したマグマでは,分化や地殻の同化が進行する.このようなイベントを繰り返す中で,深部から供給されてきたマグマが地下に滞留していたマグマにぶつかり,過熱・発泡が進行して大規模な噴火が発生する.我々は,ここに示した作業仮説を様々な視点から検証していく必要がある.

Caldera-forming eruptions are characterized by their large scale and low frequency. The question of how to prepare for such a rare, large-scale eruption poses a serious problem for the general public, administrative agencies, and volcanologists. The most commonly employed method is to investigate the past. Volcanologists seek to understand past events and to predict future developments by examining the history of eruptions. However, we face a high hurdle in preparing for such large eruptions. Using current prediction techniques, it is possible to detect the anomalous signals that immediately precede an eruption, by carefully monitoring volcanic activity. It is difficult, however, to judge whether such signals will lead to a caldera-forming eruption. In addition, it may be necessary to continue monitoring for thousands of years, until such an eruption occurs. From this reason, caldera-forming eruptions are not considered as part of the prediction program in Japan. Rather than waiting for such an eruption, it would be better to identify the processes that precede caldera-forming eruptions. This paper presents a hypothesis regarding the diversity of volcanic activity, as a basis for considering caldera-forming eruptions. The hypothesis holds that volcanic activity occurs as two end-member patterns: eruption dominant (ED) volcanism, in which magma is readily transported to the surface; and geothermal activity dominant (GD) volcanism, in which magma stagnates in the subsurface and induces geothermal activity. A spectrum of activity patterns exists between these two end members, related to the tendency of magma to ascend or to stagnate in the crust. Basic magma is stored repeatedly after intrusive events at GD volcanoes, eventually evolving to silicic magma. After repeated events, basic magma from deeper levels interacts with pre-existing magma in the chamber, causing heating, bubble formation and a huge eruption. According to this hypothesis, large amounts of magma will be found beneath volcanoes at which a caldera-forming eruption will occur in the future. It is also important to know where and why magma stops rising in the crust. The first step in understanding the preparation process of a caldera-forming eruption is to examine the hypothesis proposed in this study.

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 116(9), 463-472, 2010

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130000413572
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • Article Type
    特集
  • ISSN
    0016-7630
  • NDL Article ID
    10858134
  • NDL Source Classification
    ZM49(科学技術--地球科学--地質)
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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