The Ogoya Landslide is a large failure of 8.6 ha area in south Tokushima Prefecture, southwest Japan. Both re-sedimented humic soil and tephric loess overlie the slide deposits composed of angular boulders of sandstone. The tephric loess intercalates a thin deformed humic soil layer with AMS 14C age of 4,050±40 yrs BP, and contains entirely volcanic glass shards of the 26-29 ka Aira-Tanzawa Tephra (AT).This stratigraphy suggests that the landslide predate to 26-29 ka. Average incision rate of the upper reach of Kaifu River after the failure is estimated to less than 1.0 mm/yr.
It is difficult to make thin sections of fragile and unstable specimens that contain sulfur, clay, salt, and water by applying the conventional method in which water and oil are used. Although such liquids protect samples from the heat generated during the cutting and grinding processes, they can also damage samples, for example, due to expansions. As a solution to this problem, a new method in which liquids are not used and frictional heat is minimized has been developed; in short, samples are not influenced by liquid and heat in this new method. This method enables to make easily the least damaged thin sections of such fragile samples. Further, this method can be adapted for even complex samples that contain both hard and soft minerals, and thus helps researchers obtain all possible information that can be obtained from the samples.