Salt fretting in the valley cliff of the Asama volcano region, Japan

Abstract

AbstractOn the pumice flow deposits of the Asama volcano, Japan, many salts such as halite (NaCl), gypsum (CaSO4·2H2O), hexahydrite (MgSO4·6H2O) and mirabilite (Na2SO4·10H2O) crystallize at the base of south‐facing valley cliffs. The zone of salt efflorescence and of resulting polygonal rind correspond to the zones of notch formation and high water content. The main conditions for salt crystallization and polygonal rind formation are: (1) the existence of groundwater containing a high concentration of Cl−, SO, Ca2+, Mg2+, and Na+; (2) a valley cliff material with a high capillary action and small tensile strength; and (3) low humidity and a high ground‐surface temperature derived from the direct incidence of sunshine. Given the right conditions, salt weathering can occur not only in the arid regions but also in humid, temperate inland regions.