北海道クッタラ火山登別地熱地域の水蒸気噴火 : 1663年以降の活動 Multiple Vent-forming Phreatic Eruptions after AD 1663 in the Noboribetsu Geothermal Field, Kuttara Volcano, Hokkaido, Japan

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Abstract

北海道クッタラ火山,登別地熱地域の最も新しい水蒸気噴火堆積物(Nb-a)の調査を行い,その分布域と噴火様式を解明した.調査は登別地熱地域全域の71地点で手掘りトレンチ(深度<90cm)を掘削して行った.水蒸気噴火堆積物は,最大層厚68cmで,変質した岩石片と細粒なマトリクスからなり,有珠山b降下軽石(Us-b,西暦1663年)を覆う.この水蒸気噴火堆積物は,北北西-南南東に伸長する850×1250mの範囲に分布し,その層厚と最大粒径は,複数の爆裂火口(日和山山頂,大湯沼,笠山北,奥の湯,鉄泉池)に向かって増大する.登別地熱地域では,西暦1663年以降(17世紀末~19世紀ごろ),複数の地点で水蒸気噴火が起き,北北西-南南東方向に配列する複数の火口が形成されたと考えられる.

The Noboribetsu geothermal field (area 1 × 1.5 km) is located in the western part of Kuttara volcano, southwestern Hokkaido, Japan. Seventy-one shallow trenches (< 90 cm deep) were systematically dug within the geothermal field, in order to study the stratigraphy and distribution of the most recent phreatic fall deposit (the Nb-a deposit) erupted from the field. The Nb-a deposit (< 68 cm thick) consists of altered dacitic lithic clasts in a fine-grained clay-rich matrix. The deposit overlies the Us-b tephra that was emplaced in AD 1663. Stratigraphic sections constructed from the 71 trenches indicate that the deposit is distributed within an elliptical area measuring 850 × 1250 m across and extending NNW-SSE. Isopach and maximum-grain-size isopleth maps indicate that the deposit increases in thickness and maximum-grain-size toward several explosion craters. These data suggest that phreatic eruptions, through multiple vents, occurred in the Noboribetsu geothermal field after AD 1663.

Journal

  • BULLETIN OF THE VOLCANOLOGICAL SOCIETY OF JAPAN

    BULLETIN OF THE VOLCANOLOGICAL SOCIETY OF JAPAN 60(2), 241-249, 2015

    The Volcanological Society of Japan

Codes

  • NII Article ID (NAID)
    110009975995
  • NII NACSIS-CAT ID (NCID)
    AN10512786
  • Text Lang
    ENG
  • ISSN
    0453-4360
  • NDL Article ID
    026579892
  • NDL Call No.
    Z15-101
  • Data Source
    NDL  NII-ELS  J-STAGE 
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