ABSTRACT
Sassa (1984, 1985, 1989) suggested that the mechanism of creep movement of the Zentoku landslide. Shikoku, might be caused by underground erosion. However, the reason why this landslide has continued to move for many years, was not yet well understood. To study the influence of underground erosion at this site, continual monitoring of suspended sediment and water discharge from a groundwater outlet (i.e. a spring) has been implemented. The amounts of sediment discharge were clarified. The locations of groundwater flow paths were determined by inserting a seismograph into a borehole. Slope deformation was monitored by means of a borehole inclinometer. From these results, the mechanism of creep movement is an interrelated chain process that combines underground erosion caused by landslide activity with landslide activity caused by underground erosion. Thus, landslide activity increases erosion susceptibility and transportation of soils within the mass, and underground erosion causes instability of the landslide mass, in turn.
