四国島における大規模崩壊地形の分布と地域特性  [in Japanese] The distribution of Landforms Caused by Large-scale Mass Movement on Shikoku Island and Their Rcgional Characteristics  [in Japanese]

Through the use of aerial photographs as a starting-point the writer studied the distribution of landforms caused by large-scale mass movement (LMM), defining the regional characteristics of Shikoku and drawing the following conclusions. 1) There are 1,647 LMMs on Shikoku Island (each of whose total volume exceeds 10^5 m^3), 38.4% of whose sediment exceeds 10^6 m^3. Of the 1,647 LMMs 5.3% seen to have been formed with in the last several hundred years. Of these most were small in scale. 2) The Mikabu Zone has the highest density of LMMs. There are more than 40 sites per 100 km^2. Second to the Mikabu Zone is the Sambagawa Zone, then, the Chichibu Zone, the Shimanto Zone, and the Ryoke Zone in that order. The mass movement in the Mikabu Zone is mainly of the land creep type, and the other zones generally being of to the rapid landslide type. The writer thinks the cause being lithology and or the rate of the land upheaval, 3) Some of the ancient LMMs are related to ridge-top depressions, but generally the characteristics of the ancient LMMs are different from the landforms caused by recent large-scale landslides due to heavy rainfall. 4) In general, the greater the size of the mass movement the more it is related to the geological structure, and these are clearly related to the bedding plane slide. The typical example of this is on the Asan Mountain Range.