Japan is one of the famous countries which has many volcanoes which often provide sulfur-related materials to the surrounding environments. During Miocene, many submarine volcanoes in the Japan Sea erupted frequently and the related tuff rocks were deposited on the base of the seafloor. Then, those Miocene rocks uplifted and characterized hills in some areas in Japan. Those tuffaceous rocks do not have high strength and ancient people could use the rocks for their houses, tombs, etc. One of such archaeological sites, Yoshimi-Hyaku-Ana, is an important cultural property in Japan. The site is composed of more than 100 ancient graves of 6-7 centuries cut on the hill slope discovered around 150 yrs ago, and composed of artificial caves dug from 1941 to 1945 at the bottom of the hill as well. Most of the trees were cut on the hill during the excavation, and then the hill slopes were exposed and started deteriorating. The weathering mechanism is salt crystallization, and the cave is suffering from severe salt efflorescence. These salt efflorescence’s are much in dry winter but less in humid summer. According to Takaya et al. (2010), those minerals are granularly effloresced alunogen (Al2(SO4)3.17H2O), gypsum (CaSO4.2H2O), halotrichite (FeAl2(SO4)4.22H2O), sodium alum (NaAl(SO4)2.12H2O) and epsomite (MgSO4.7H2O), Jarosite (KFe3(SO4)4.(OH)8).Halotrichite, sodium alum and epsomite damaged the walls most severely, especially in the dry winter. The weight of debris produced by salt crystallization from the inner wall was greater than that from near entrances, which is an unusual phenomenon. On the contrary, the cave wall at the other entrance where weak sunshine, has only gypsum been observed (Ariga et al., 2015). From these results, salts have their own characteristics of solubility and equilibrium relative humidity, and this controls the degree of debris production.
Mots clés : Salt weathering|tuff|sulphate|alnogen|Yoshimi-Hyaku-Ana
A105603CO