Japan Geoscience Union Meeting 2022

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H (Human Geosciences ) » H-GM Geomorphology

[H-GM02] Geomorphology

Mon. May 23, 2022 10:45 AM - 12:15 PM 201B (International Conference Hall, Makuhari Messe)

convener:Hitoshi SAITO(College of Economics, Kanto Gakuin University), convener:Tsuyoshi Hattanji(Faculty of Life and Environmental Sciences, University of Tsukuba), Thomas Parkner(University of Tsukuba, Graduate School of Life and Environmental Sciences), convener:Naoko Nagumo(International Centre for Water Hazard and Risk Management, Public Works Research Institute), Chairperson:Thomas Parkner(University of Tsukuba, Graduate School of Life and Environmental Sciences), Hitoshi SAITO(College of Economics, Kanto Gakuin University), Naoko Nagumo(International Centre for Water Hazard and Risk Management, Public Works Research Institute)


11:45 AM - 12:00 PM

[HGM02-05] Study on the relationship between chemical weathering indices and clay-silt rates of the slope soil layers in granitic bedrock areas

*Chiaki T. Oguchi1, Konomi Nakamura2, Tsuyoshi Wakatsuki3 (1.Institute for Environmental Science and Technology, Graduate School of Science and Engineering, Saitama University, 2.Department of Engineering, Saitama University, 3.the National Research Institute for Earth Science and Disaster Resilience (NIED))

Keywords:granite, chemical weathering, physical weathering (mechanical weathering), weathering index, clay, silt

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.