バッドランド斜面における侵食プロセスに関する地化学的検討 : 台湾南部, 泥火山が分布する古亭坑層での調査 Geochemistry of Erosion Processes on Badland Slopes : A Case Study of the Gutingkeng Formation Where Mud Volcanoes are Distributed in Southern Taiwan

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 Understanding erosion processes is important to prevent natural disasters such as slope failure and bedrock erosion in immature sedimentary rocks. Pliocene–Pleistocene illite-rich, non-smectite mudstone of the Gutingkeng Formation is distributed over 250 km<sup>2</sup> in southern Taiwan, forming badlands (locally called moon-world) with mud volcanoes nearby. These volcanoes erupt saline water and natural gas, and producing a Na<sup>+</sup>, Ca<sup>2+</sup>, Cl<sup>-</sup>, and SO<sub>4</sub><sup>2-</sup> rich unsaturated Popcorn crust, which covers the mudstone slope surfaces in the moon-world area. In the crust porewater, ion strength reaches about 10 mol/L; zeta potential on particle surfaces shows a highly positive voltage. Repulsion occurs between particles under this high voltage in the crust, which is rapidly slaked to form mud by heavy precipitation. The zone that is rapidly slaked by precipitation reaches 10-20 cm beneath the crust surface. Ion strength of porewater of fresh mudstone is 0.5 mol/L approaches 0 mV (range 0.2-0.5 mol/L, pH 4-6). The surface charge of particles decreases with the infiltration of precipitation into the crust and fresh rock, with a minus surface charge occurring with increased rain infiltration. This leads to many cracks forming on the surface of mudstone, which is different from the mechanism of rapid slaking.<br> Evaporation from the 10-20 cm-thick zone between the crust and the underlying fresh mudstone would stop if water was not supplied from depth, which is supported by in-situ measurements of water evaporation in the field. These mudstones erode readily under high precipitation because of the repulsion caused by the high ion strength of porewater. High-salinity porewater including mudstone is distributed near the active mud volcanoes where saline water rises and there is a rapid uplift rate. Rapid slaking occurred with some elements in the concentrated crust and near the surface drying zone.

収録刊行物

  • 地學雜誌

    地學雜誌 118(3), 511-532, 2009-07-07

    公益社団法人 東京地学協会

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各種コード

  • NII論文ID(NAID)
    10030365781
  • NII書誌ID(NCID)
    AN00322536
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    0022135X
  • NDL 記事登録ID
    10386654
  • NDL 雑誌分類
    ZM41(科学技術--地球科学)
  • NDL 請求記号
    Z15-169
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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