| Budget Amount *help |
¥4,680,000 (Direct Cost: ¥3,600,000、Indirect Cost: ¥1,080,000)
Fiscal Year 2018: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2017: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
Fiscal Year 2016: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
Fiscal Year 2015: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
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| Outline of Final Research Achievements |
Unconsolidated superficial tephra deposits that cover the volcanic edifices have great potential for generating serious sediment disasters. The generation mechanism and frequency of landslides on tephra-rich slopes were examined based on tephrostratigraphic and historical studies. Most of the landslides were shallow soil slips (<2 m thick) in unconsolidated tephra deposits overlying lava flows and pyroclastic rocks in the cases of Aso caldera in July 2012 and Izu Oshima volcano in October 2013. Physical differences of tephra deposits above and below the rupture surfaces including grain size, hardness and permeability promote the retention of rainwater in the upper layer, leading finally to failure and mobilization of the saturated mass. Tephra chronology and radiocarbon dating on paleosols along the succession suggest that rainfall-induced landslides and the associated lahars on the eastern wall of Aso caldera occurred at an interval of 400-1800 years.
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