[M-IS13] [JJ] 山岳地域の自然環境変動

[MIS13-18] 日本アルプスにおける大規模岩盤崩壊: 大起伏山岳地形の形成過程における気候変動の影響

★招待講演

*松四 雄騎¹、苅谷 愛彦²、原山 智³、松崎 浩之⁴ (1.京都大学防災研究所、2.専修大学文学部、3.信州大学理学部、4.東京大学総合研究博物館)

キーワード：岩盤崩壊、露出年代測定、河川の下刻、氷期-間氷期サイクル、準動的平衡状態、地形発達

Several recent heavy rainfall events in Japan reveal the sensitive nature of deep-seated landslide occurrence to rainfall anomaly, which invokes potential influence of both of natural and anthropogenic climate change on such catastrophic mass movements in mountainous terrains. A combination of river incision under long-term tectonic activity and episodic deep-seated landsliding by climate forcing may progress the mountainous landscape evolution. The present study attempts to verify the role of climate change in shaping the mountainous landscapes by dating of paleo bedrock landslides using terrestrial cosmogenic nuclide ¹⁰Be in Japanese Alps. Samples for exposure dating were collected from top of a boulder on landslide deposits or bare rock slip surface exposed since the landslide. Effect of snow shielding on nuclide production were corrected for accurate determination of exposure ages, and the correction procedure was calibrated by ¹⁴C dating for some deposits yielded by the identical landslide event. The ages of landslide deposits concentrated in Holocene epoch especially at just after the Termination I (transition from the last glacial to present interglacial stage) and also recent period during the last 3 kyr. These results imply that climate change has potentially instigated the landslide occurrence and thus contributed to form and maintain bedrock dominated steep topography adjacent to incised valleys in mountainous ranges.