2018 Volume 71 Issue 2 Pages 34-41
Early morning on April 11, 2018, in the Yabakei area of Nakatsu city, Oita prefecture, an unexpected fatal landslide occurred without any usual causes such as rainfall and earthquake. According to the Oita prefecture's announcement, 4 houses were damaged, and 6 residents were killed. The rain observatory in the vicinity of the landslide slope recorded 4.5 mm and 1.5 mm rainfall on April 6 and 7, respectively. Rainfall had not been observed April 8 to April 11. With a simple in-situ survey, the landslide had a measured length of approximately 210 m, a height of about 120 m, a width of about 110 m, and a scarp of about 30 m in height. Currently, the major cause of the landslide was estimated to be weathered clay layer formed from tuff by mineral-groundwater reaction.