Japan Geoscience Union Meeting 2022

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[J] Oral

H (Human Geosciences ) » H-DS Disaster geosciences

[H-DS11] Geohazards in humid, tectonically active countries and their precursors

Mon. May 23, 2022 3:30 PM - 5:00 PM 201B (International Conference Hall, Makuhari Messe)

convener:Satoru Kojima(Department of Civil Engineering, Gifu University), convener:Taro Uchida(University of Tsukuba), Yoshihiko Kariya(Department of Environmental Geography, Senshu University), Chairperson:Taro Uchida(University of Tsukuba), Yoshihiko Kariya(Department of Environmental Geography, Senshu University), Satoru Kojima(Department of Civil Engineering, Gifu University)

4:30 PM - 4:55 PM

[HDS11-11] Impact of continuous sediment supply from large landslide scars in the southern Japanese Alps

★Invited Papers

*Ryoko Nishii1, Fumitoshi Imaizumi2, Yuichi S. Hayakawa3 (1.Niigata University, 2.Shizuoka University , 3.Hokkaido University)

Keywords:large landslide, sediment supply, LiDAR data, gravitational deformation

The Japanese Alps located in humid and tectonically active regions has high denudation rates, which were estimated from sedimentation rates in dam reservoirs and concentration of terrestrial cosmogenic nuclides. One of direct causes of high denudation rates is probably the occurrence of new large landslides. However, few studies have paid attention to impact of continuous sediment supply from bare grounds after the landslide events. To clarify sediment supply from landslide scars after the original events, we examined spatial distribution and volume lost of large landslides (≧104 m2) in Hayakawa River basin (ca. 500 km2), southern Japanese Alps using LiDAR data in 2009 and 2015. In addition, focusing on continuities of landslide, landslides were classified into two types: new type (NT) formed between 2009 and 2015 and persistent type (PT) formed before 2009. Total 57 landslides were found for analysis, eight of which were NT and the other 49 were PT. Total volume lost from 2009 to 2015 reached about 4.4×106 m3. NT produced only 20% of the volume. In contrast, three largest PT landslides, which have already existed in early 1900s, produced about 70% of the total volume lost. The high distribution density of sackung scarps around the three PT suggests that decrease in rock mass strength with deep-seated gravitational slope deformation facilitates active sediment supply. Therefore, PT landslides seem to have more impact on sediment supply into Hayakawa River basin.