[H-GM02] Geomorphology

[HGM02-05] 花こう岩質岩石からなる斜面土層の風化指標値と粘土・シルト率との関係に関する研究

*小口 千明¹、中村 好²、若月 強³ (1.埼玉大学大学院理工学研究科、2.埼玉大学工学部建設工学科、3.防災科学技術研究所)

キーワード：花こう岩、化学的風化、物理的風化、風化指標、粘土、シルト

The phenomena of rock weathering usually combine chemical and mechanical (physical) weathering. This study examines which type of weathering is dominant and appears the characteristics of slope soils in several granitic base-rock areas. Rock samples are pre-collected in the granite areas of Nagiso, Iwakuni, Hiroshima, and Ishigaki, Japan. The relationships between the several chemical weathering indices such as CIA (Chemical Index of Alteration), Si/Al ratio, MWPI (Modified Weathering Potential Index), and PI (Product Index), and the particle size distribution were investigated. The results show that the CIA values and the Si/Al ratios are proportional to the clay-silt contents in those rocks and soils. In addition, those values have correlated with the climatic conditions of sampling sites. The CIA values indicate the dissolution degree of alkali/alkali earth elements from rocks and soils, whereas the Si/Al ratios indicate mineral alteration to clays. Therefore, it is considered that the larger the decomposition of rocks and chemical index changes, the chemical weathering are dominant.