Landslides Triggered by the July 2012 Torrential Rain in Aso Caldera, Southwestern Japan

Abstract

Intense rainfall on 11-12 July 2012 （maximum total 572 mm; maximum 4-hour rainfall 385 mm） triggered numerous landslides and associated lahars in Aso caldera, central Kyushu, south- western Japan. Most of the landslides were concentrated in the eastern part of Asodani Valley, at the northern part of Aso caldera. The landslides were divided into three types: landslides occurring at steep caldera walls, landslides generated on the slopes of the post-caldera central cones of Aso Volcano and landslides occurring on steep slopes of Nekodake Volcano. Most of the landslides were shallow （about 1-2 m thick） soil slips in unconsolidated fallout tephra layers overlying lava and welded Aso pyroclastic-flow deposits, and mobilized completely into lahars. The lahars eroded talus slopes and/or channel side slopes and transported boulders, which damaged houses and caused fatalities at some sites. Similar landslide and associated lahar disasters occurred at Aso Volcano in June 1953, July 1990 and June 2001. The characteristics of landslides and lahars provide important information for preventing or mitigating future similar disasters in the Aso caldera region. Key