Rainstorm-induced landslides at Kisawa village, Tokushima Prefecture, Japan, August 2004

Heavy rain fell on the Shikoku area during Typhoon Namtheun, setting a new record for daily rainfall in Japan of 1317 mm. The rain which peaked at 120 mm/h, triggered numerous landslides in the Nakagawa basin of Tokushima Prefecture, Japan on August 1, 2004. Among them, four large, rapid, long-runout landslides were triggered at Kisawa village. Two people were caught in one landslide and disappeared without trace, and there was much property damage. Ring-shear tests on samples from the landslides showed that shear resistance was greatly reduced by high pore-water pressure after shear failure was triggered by the increase in ground-water level during the rain.