Slope evolution Processes of Landslides around the Quaternary Volcanoes in the Tohoku district, Japan.

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Other Title
  • 東北地方における第四紀火山周辺の地すべりの発達
  • トウホク チホウ ニ オケル ダイ4キ カザン シュウヘン ノ ジスベリ ノ ハッタツ ヤマガタケン ヒジオリ カルデラ シュウヘン オ レイ ト シテ
  • A Case Study in the Surrounding area of the Hijiori caldera, Yamagata Prefecture
  • 山形県肘折カルデラ周辺を例として

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Abstract

Slope evolution processes of landslides around the Quaternary volcanoes have been studied in the surrounding area of the Hijiori caldera in the Central Tohoku district, Japan. These landslides are located on the cuesta or crest slopes composed of Tertiary mudstone/sandstone layers overlaid by pyroclastic flow deposits that have been dissected at the toe and side part of the slopes. They are slipping along the bedding plane. They originated from the primary rockslides just before the deposition of pyroclastic flow from the caldera.<BR>The evolution processes of the Hirane landslide, 5km north from the Hijiori caldera were studied from the slope stability calculation both by the Fellenius and the simplified Janbu three-dimensional methods (Ukai, 1987). Though an earthquake with more than 700 gal can induce a landslide, it is indicated that the primary rockslide could occur in the mudstone layers by the earthquake with 300-500 gal at the eruption time of the pyroclastic flow. Weakening of the rocks by pre-eruption earthquakes and the location of the landslides on the crest of cuesta slopes might have been the cause.Just after this slide, the slope had been buried by the thick pyroclastic flow deposits and got higher stability. Continuous erosion of the pyroclastic flow deposits from the toe part of the landslide slopes has induced the instability of the primary rockslide. Stability calculation by using the residual shear strength obtained from ring shear tests indicates present unstable condition of the landslide. The slope evolution processes mentioned above could be applied to the origin of the other present large-scale landslides around the Quaternary volcanoes in the Tohoku district.

Journal

  • Landslides

    Landslides 38 (4), 310-317, 2002

    The Japan Landslide Society

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