史跡・吉見百穴の坑道壁面における凝灰質岩の塩類風化とその影響要因

概要

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To clarify the rate and mechanism of salt weathering of tuffaceous rock, monthly observation were made over one year on tunnel wall at the Yoshimi Hyaku-Ana, historic site in central Japan. Products of weathering that had fallen were collected, and then debris were separated from salts by dissolving in water and weighed. The amount of debris from the north-facing wall was much greater than from south-facing wall. The peak season at the north-facing and south-facing wall was from spring to summer and early spring, respectively. During the same period, alunogen (Al_2(SO_4)_3・17H_2O) was abundant. Therefore, the crystallization of alunogen contributed to debris production from the wall. At the north-facing wall, feature of weathering was different between the upper and lower of wall; crystallized in early spring on the lower part of wall salts, in early summer on the upper part; amount of debris was smaller from the lower than from the upper. In addition, the hardness of wall surface was larger in the lower than in the upper. The features of south-facing wall were similar to the lower of north-facing wall. We recognized two types of breakdown of rock; (1) granular disintegration on the upper part of north-facing wall, and (2) contour scaling on the south-facing wall and lower part of north-facing wall. The rate of salt weathering was influenced by physical and mechanical properties which the breakdown phenomenon possessed.
2011-07-25