Abstract
To evaluate quantitatively debris production due to salt weathering of tuff, monthly observations were made over 1 year on a tunnel wall in Yoshimi Hyaku-Ana (100 caves of Yoshimi, Saitama prefecture), an historic cliff tomb site in central Japan. Spalls including salts were collected, separated into fallen debris and salts by dissolving in water, and weighed. The amount of debris is much greater from winter to early spring at lower temperature and humidity due to weathering in the form of granular disintegration. During the same period, sodium alum (NaAl (SO4) 2·12H2O) was abundant, and halotrichite (FeAl2 (SO4) 4·22H2O) was found on the wall. Poorly soluble salts such as gypsum (CaSO4·2H2O) and jarosite [ (K, Na) Fe3 (SO4) 2 (OH) 6] were observed throughout the year. Therefore, the crystallization of sodium alum and halotrichite contributed to debris production. We found a one-dimensional correlation in weight between fallen salts and debris, and greater amounts of debris were produced from the wall when more abundant salts had been crystallized.
