ABSTRACT
A large-scale collapse has been occurring in a crystalline schist area, called Tue Valley, in the mountainous region of Shikoku. The topographical and geological features of the Valley, the mechanism of occurrence of large-scale collapse, and the present condition of the slopes were investigated and analyzed. The main slope was found still to be unstable. Topographical and geological factors inherent in the slope such as geological structure, formation of weak lines, weathering, creeps of bedrock, upheaval, and erosion by streams have been playing important roles in the occurrence of large-scale collapse. Earthquakes and heavy rainfalls were ascertained as inducing factors to the collapse. Various types of secondary movement of debris involving collapse, landslides, and debris flows are still occurring. Many potential blocks, or debris masses, are continuously sliding. Collecting and accumulating such data will help us to enhance erosion control planning in future.
