北海道中央部,旭岳の形成史:特に完新世,後期活動の水蒸気噴火履歴および噴火様式について  [in Japanese] Eruptive history of Asahidake Volcano, central Hokkaido: New study of the stratigraphy and eruption ages of the Asahidake late stage products.  [in Japanese]

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Author(s)

    • 石毛 康介 Ishige Kosuke
    • 北海道大学大学院理学院自然史科学専攻 Department of Natural History Sciences, Graduate School of Science, Hokkaido University
    • 中川 光弘 Nakagawa Mitsuhiro
    • 北海道大学大学院理学院自然史科学専攻 Department of Natural History Sciences, Graduate School of Science, Hokkaido University
    • 石塚 吉浩 Ishizuka Yoshihiro
    • 産業技術総合研究所地質調査総合センター活断層・火山研究部門 Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan, AIST

Abstract

<p>大雪火山群で活動を続ける旭岳について,後期更新世~完新世のマグマ噴火および水蒸気噴火堆積物の層序を明らかにした.旭岳のマグマ噴火は,1.5万年から9千年前頃が最盛期で,それ以降,マグマ噴出率は低下していく.約5,000年前以降にマグマ噴火は発生していない.その後旭岳では,約2,800年前に規模の大きな水蒸気噴火があり,現在の地獄谷爆裂火口が形成された.最後の噴火は,約700年前の小規模な水蒸気噴火である.旭岳は現在噴気活動が活発ではあるが,最近2,800年間でみると噴火頻度は低い.しかしながら多数の観光客や登山者が訪れる現状を考慮すると,小規模な噴火の可能性に留意しておく必要がある.</p>

<p>The eruptive history and eruption style of Asahidake volcano, the youngest volcanic edifice of the Taisetsu Volcano Group, central Hokkaido, Japan, are investigated to evaluate its long-term volcanic hazards. The Asahidake edifice consists of a pyroclastic cone whose growth is associated with lava effusions since the late Pleistocene. The eruption rate was relatively high, with an estimated 1.0 km<sup>3</sup> dense rock equivalent (DRE)/ky from 15 ka to 9 ka that rapidly decreased to 0.03 km<sup>3</sup> DRE/ky from 9 ka to present. After the latest magmatic eruption ca. 5 ka, there was a 2 ky dormant period that was followed by a large-scale phreatic eruption ca. 2.8 ka, which possessed the following eruption sequence. The sequence began with edifice collapse that produced a debris avalanche and formed the Jigokudani horseshoe-shaped crater, followed by phreatic explosions. Lahar flows then effused from many small craters and fissures that had formed in and at the opening part of the Jigokudani crater. This eruptive activity decreased after the eruption sequence. We recognize that the most recent small-scale phreatic eruption occurred ca. 0.7 ka. Although the current fumarole activity is remarkable, it appears that the eruptive activity has declined considerably since the 2.8 ka eruption. Considering the temporal change in eruptive activity, it is possible that the activity of Asahidake volcano has monotonically decreased over the past 10,000 years. However, in the context of volcanic hazard mitigation, it should be noted that small-scale phreatic explosions and/or effusions of lahar similar to the 0.7 ka eruption might potentially occur and endanger tourism activities.</p>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 124(4), 297-310, 2018

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130007413137
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    029098859
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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