北海道駒ヶ岳火山, 先歴史時代噴火活動史の再検討  [in Japanese] Reevaluation of the pre-1640 A.D. eruptive history of Hokkaido-Komagatake volcano, northern Japan  [in Japanese]

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Abstract

北海道駒ヶ岳火山北西~北東山麓部に露出する噴出物の層序,<sup>14</sup>C年代,岩石学的特徴を検討した.これまで40~6 cal kaの間には4層の噴火堆積物が識別されていたが,今回新たに7層の噴火堆積物(P7~P1)を識別した.それらの噴火年代は,約19 cal ka(P7),約17.7 cal ka(P6),約17.4 cal ka(P5),約14.8 cal ka(P4),約12.8 cal ka(P3),約6.5~6.3 cal ka(P2,P1)である.北海道駒ヶ岳火山の活動は,6,000年以上の長い休止期によって少なくとも4つの活動期(39 cal ka 以前, 20~12.8 cal ka, 6.8~6.3 cal ka, 1640 AD以降)に区分される.これら4つの活動期は本質物質の全岩化学組成も異なっている.最近3回の活動期は,4~6回のマグマ噴火からなり,規模の大きな噴火で始まり,その後より規模の小さい噴火を繰り返していたことが明らかになった.

We propose a new 40 thousand year-old eruption history of Hokkaido-Komagatake volcano, northern Japan, from new field observations, radiocarbon dating of charcoal woods and whole-rock chemistry of juvenile materials. In previous studies, eight distinct plinian eruption units have been recognized in the last 40 thousand years (Ko-a, 1929 AD; Ko-c1, 1856 AD; Ko-c2, 1694 AD; Ko-d, 1640 AD; Ko-f, 6.3 cal ka; Ko-g, 6.8 cal ka; Ko-h, 20 cal ka; Ko-i, 39 cal ka). Our study has revealed seven new eruption units between Ko-d and Ko-i in the northern flank area of the volcano. Eruption ages of the new units are estimated to be: P1 (6.5−6.3 cal ka); P2 (6.5−6.3 cal ka); P3 (ca. 12.8 cal ka); P4 (ca. 14.8 cal ka); P5 (ca. 17.4 cal ka); P6 (ca. 17.7 cal ka); and P7 (ca. 19 cal ka). The eruption history can be divided into four stages, separated by long periods of dormancy: pre-39 cal ka, 20 cal ka to 12.8 cal ka, 6.8 cal ka to 6.3 cal ka, and post-1640 AD. Each of the four stages is characterized by distinct whole-rock chemistry. The last three stages are characterized by an initial large eruption and subsequent medium to smaller scale eruptions. Our new findings could provide important background information and context for understanding the present state of Hokkaido-Komagatake volcano.

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 114(7), 336-347, 2008-07-15

    The Geological Society of Japan

References:  20

Cited by:  1

Codes

  • NII Article ID (NAID)
    110006830201
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    00167630
  • NDL Article ID
    9602874
  • NDL Source Classification
    ZM49(科学技術--地球科学--地質)
  • NDL Call No.
    Z15-174
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
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