Assessment of climate-induced degree of chemical weathering in some granite and granodiorite slopes of Japan

Abstract

The widespread hillslope failures largely depend on the degree of weathering. Different weathering processes, especially chemical weathering, are the consequence of the variation of climatic factors, e.g., temperature and precipitation. The present study describes the various chemical and mineralogical properties of bedrock and soil samples from granite and granodiorite landslide areas under continental temperate, temperate and subtropical climate regions in central to southwestern Japan. The XRD and SEM–EDS analyses were carried out for mineralogical and chemical analyses. It is evident that bedrock samples contain quartz, k-feldspar, plagioclase, biotite and amphibole, whereas the slip surface and the upper surface soil samples are enriched with kaolin minerals, mica clay minerals and vermiculite or 14 A intergrade minerals. Mobile elements showed decreasing values, whereas immobile elements showed increasing values with progressive weathering due to leaching (dissolution of cations) in all studied areas. The analysis of weathering indices indicated weathering progress in the order from bedrock, slip surface and upper surface soil. The relationship of mean annual air temperature and precipitation for 30 years (1981–2010) with CIA and Si–Al ratio indices showed that CIA values increased and Si–Al ratio decreased with increasing temperature whereas, precipitation did not follow that identical trend. Therefore, temperature is the key factor for chemical weathering in all cases and is more prominent on granodiorite areas than granite areas.