CLAY MINERALOGICAL DIFFERENCE BETWEEN BEDROCK AND COLLUVIAL-SOIL SLIDES IN THE NORTHERN PART OF NAGASAKI

EGASHIRA K.

Two types of landslide, namely bedrock and colluvial-soil slides, are found in the northern part (Kitamatsuura-gun) of Nagasaki Prefecture. The bedrock slide has a slip surface in the tuffaceous coal seams intercalated in the Miocene sediments composed of sandstone and mudstone. The colluvial-soil slide occurred in colluvial materials overlying bedrock and movement was for a relatively short distance. The samples were collected from sites undergoing bedrock or colluvial-soil slide and analyzed for physical, chemical and mineralogical properties. A large clay mineralogical difference was found between the samples of bedrock and colluvial-soil slides, while such properties as particle-size distribution and proportions of exchangeable cations were not substantially different. The sample from the site undergoing a bedrock slide was characterized by a high amount of smectite, and the samples from colluvial-soil slides contained mica, kaolinite, and less smectite. Such clay mineralogical difference may partly be related to the small scale of colluvial-soil slides compared to bedrock slides.

CLAY MINERALOGICAL DIFFERENCE BETWEEN BEDROCK AND COLLUVIAL-SOIL SLIDES IN THE NORTHERN PART OF NAGASAKI

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