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火山角礫岩からなる急崖に発達するノッチ・タフォニの形成プロセスと岩盤崩落との関係
─香川県高松市五剣山の例─
西山 賢一横田 修一郎長谷川 修一菅原 大介
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126 巻 (2017) 4 号 p. 425-437

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 Morphological features of notches and tafoni, which are well developed on volcanic breccia cliffs of Miocene Setouchi volcanic rocks in Kagawa, Shikoku, Japan, are described. The moisture content of a rock surface shows the highest value at the concave roof portion. The presence of a salt, such as gypsum, on notch walls suggests these notches are formed by salt weathering under a high humidity. Notches and tafoni develop to produce a visor overhang on a steep cliff, and such unstable blocks occasionally collapse as rock falls. In addition to the development of notches and tafoni, cracks within volcanic breccia can also cause rock falls. Consequently, the rate at which notches deepen due to salt weathering and the spacing of tension cracks may control the frequency of rock falls from these cliffs.

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© 2017 公益社団法人 東京地学協会
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