Study on the elucidation of formation mechanism of expandable clay minerals and the forecast of "Shirasu" cliff collapse.

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We collected many samples from "Shirasu" cliffs, and checked them by X-ray diffractometer.In the collapsed pyroclastic flow deposits fairly amount of 10 Å-halloysite and/or smectite was included., but in the deposit remaining on the cliff, those expandable day minerals do not exist much. In the samples collected from Harihara district where landslide occurred recently, much amount of 10 Å-halloysite is included. In the samples collected from Aira town where landslide also occurred recently, much amount of 10 Å-halloysite is included. In the sediments at Kagono, Oita Prefecture, much amount of smectite are included and many landslides occurred so far.These phenomena indicate that these expandable clay mineras absorbed much water in their interlayers after heavy rain, and deposits expand ed creating many cracks. As a result, collapse of cliffs and/or landslide occur. So we studied on the formation mechanisms of expandable clay minerals, especially on smectite, and we have succeeded on forming smectite from volcanic glasses and pyroclastic flow deposits under atomospheric pressures and under low temperature and low pressure conditions.