Overview of the Yabakei landslide occurred on April 11th 2018 in Nakatsu city, Oita prefecture, Japan

Tomoyoshi MIYAZAKI, Masayo SAWADA, Naoki MATSUOKA, Yoshimichi TACHIKAWA, Shigenori TAKASHIMA, Yasunori YOSHIDA, Shin-ichiro HAYASHI, Takahisa FURUICHI, Mio KASAI and Nobutomo OSANAI


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, 4houses were damaged, and 6residents were killed. The rain observatory in the vicinity of the landslide slope recorded 4.5mm and 1.5mm 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 approximately210m, a height of about120m, a width of about110m, and a scarp of about30m in height. Currently, the major cause of the landslide was estimated to be weathered clay layer formed from tuff by mineral‐groundwater reaction.

Key words

Oita prefecture, the Yabakei landslide, Yabakei Pyroclastic Flow Deposits, ground water