An analytic investigation of periglacial topography in Horonobe region, Hokkaido

DOI Web Site 4 References
  • Hanatani Ikuo
    Japan Atomic Energy Agency, Nuclear Safety Research Center, Waste Disposal Safety Research Group Nikko Exploration and Development Co., Ltd.
  • Munakata Masahiro
    Japan Atomic Energy Agency, Nuclear Safety Research Center, Waste Disposal Safety Research Group
  • Kimura Hideo
    Japan Atomic Energy Agency, Nuclear Safety Research Center, Waste Disposal Safety Research Group
  • Sanga Tomoji
    Nikko Exploration and Development Co., Ltd.

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Other Title
  • 幌延地域における周氷河地形の解析的研究
  • ホロノベ チイキ ニ オケル シュウ ヒョウガ チケイ ノ カイセキテキ ケンキュウ

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Abstract

  For the geological disposal of high-level radioactive wastes, evaluation of the radionuclide migration toward the human environment associated with groundwater flow is essential in order to secure long-term safety. Therefore, Japan Atomic Energy Agency (JAEA) is implementing a program for developing methods for assessing long-term groundwater flow in regional scales. The present project is a part of the above and we conducted a study on key factors regarding changes of groundwater flow from the last glacial to the postglacial stages in the Horonobe and surrounding areas which were most likely covered by permafrost then. Specifically, geomorphological analysis was carried out using aerial photographs and a high resolution (10 m) DEM to obtain the distribution of the slopes that had been formed after the last glacial stage, and the relation between the geological conditions and the erosion depth of those slopes was analyzed.<br>  The results are summarized as follows: <br>  1) Although periglacial smooth slopes which expanded widely in Horonobe region over the last glacial stage were eroded by rainfall increase and steeper slopes had been formed in the postglacial stage, this postglacial erosion is not uniform and is strongly influenced by the geology. In other words, the drainage density is low and less than 40% of periglacial smooth slopes have been eroded to the present in the Koetoi and Wakkanai Formations while it is high and 60% or more of those slopes have already been eroded in the Yuchi and Sarabetsu Formations.<br>  2) The depths of valleys formed during the postglacial stage can be classified into two types with a comparatively shallow valley<br>  in the formations higher than Koetoi and the comparatively deep valley in the formations lower than Wakkanai. Additionally the varying processes of a river-bed altitude are different in the northern part and the southern part of the region.<br>  3) From the result of the above analysis, it is concluded that the factors which change the groundwater flow system when it shifted from the last glacial to the postglacial stage are disappearance of permafrost, rise of river-bed altitude of main stream and rainfall augmentation.

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