白亜紀防府花崗岩体で発生した土石流の分布と性状 Distribution and Characteristics of Debris Flows Occurred in the Cretaceous Hofu Granitic Region, Yamaguchi Prefecture

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 「平成21年7月中国・九州北部豪雨」によって, 後期白亜紀防府花崗岩体の分布する防府市北部と山口市中部では土石流が多発し, 防府市で14名の犠牲者が出た. 防府市北部では, 平成5年にも大雨に伴って土石流が発生し, 5名の犠牲者が出た. 本報告では, 平成21年の豪雨で発生した土石流の分布と性状を詳細に記載するとともに, 平成5年の土石流の分布と比較する. 平成21年に発生した土石流の源頭部は, 524か所中478か所が防府花崗岩体に位置する. 防府花崗岩体は岩相によって, 粗粒黒雲母花崗岩, 中粒黒雲母花崗岩, 細粒黒雲母花崗岩および花崗閃緑岩に分けられる. 単位面積あたりの土石流源頭部の数は, 粗粒黒雲母花崗岩で最も多く5.5個/km2, その他の岩相ではその約1/2以下であった. 一方, 平成5年では130か所のうち109か所が中粒黒雲母花崗岩と粗粒黒雲母花崗岩であった. 1kmメッシュの起伏量と源頭部の関係は, 平成21年と平成5年のいずれの土石流も源頭部は起伏量が201~250mの区域に集中する. 500mメッシュの接峰面図に基づくと平成21年と平成5年の源頭部はそれぞれ201~250mと101~150mに最頻値を持つ.

 Many debris flows were caused in northern Hofu and central Yamaguchi Cities, Yamaguchi Prefecture by a heavy rain, named the "Heavy Rain in Chugoku and Northern Kyushu of July in 2009" after the Japan Meteorological Agency. Late Cretaceous Hofu granitic body is widely distributed in the debris flow area. Fourteen people were killed in Hofu City by the debris flow. Debris flows were occurred also in northern Hofu City by a heavy rain in 1993, and killed four people. In this report, we describe characteristics and distribution of the 2009 debris flow in detail, and then compare the distribution to that of the 1993 debris flow. Source areas of the 2009 debris flow amount to 524, 478 of which occurred in the Hofu granitic region. From rock facies, the granitic body is tentatively classified into coarse-, medium- and fine-grained biotite granites, and granodiorite. Number of the source area per unit area is the most in the coarse-grained biotite granitic region, with the maximum being calculated to be 5.5/km2. The number in the other types of granites is estimated to be less than about one-half of that in the coarse-grained granite. On the other hand, Source areas of the 1993 debris flow amount to 130, 109 of which occurred in the region of medium- and coarse-grained biotite granites. The relationship between the amount of topographic relief of 1 km meshes and the location of the source area indicates that both the 2009 and 1993 debris flows concentrated on the mesh of the elevation interval 201-250 m. Based on the analysis of a summit-level map, the histogram of the 2009 and 1993 debris-flow number have the modes in the elevation interval of 201-250 m and 101-150 m, respectively.

収録刊行物

  • 応用地質

    応用地質 52(6), 248-255, 2012-02-10

    日本応用地質学会

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各種コード

  • NII論文ID(NAID)
    10030134862
  • NII書誌ID(NCID)
    AN00026635
  • 本文言語コード
    JPN
  • 資料種別
    NOT
  • ISSN
    02867737
  • NDL 記事登録ID
    023530392
  • NDL 請求記号
    Z15-263
  • データ提供元
    CJP書誌  NDL  IR  J-STAGE 
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