Hazard mapping based on terrain chronology and gravitational slope deformation ratio

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K01211
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Geography
• Research Institution: Yamagata University
• Principal Investigator: YAGI Hiroshi 山形大学, 地域教育文化学部, 教授 (40292403)
• Co-Investigator(Kenkyū-buntansha): 佐藤 浩 日本大学, 文理学部, 准教授 (60360468) ; 若井 明彦 群馬大学, 大学院理工学府, 教授 (90292622) ; 松四 雄騎 京都大学, 防災研究所, 准教授 (90596438)
• Research Collaborator: Dangol V. Trivban University, Trichandra Campus, Prof.
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: Himalaya / 重力変形 / 地すべり / 地形発達 / 下刻 / 土石流 / 最終氷期後半 / 地変

Outline of Final Research Achievements

Geomorphological evolution in the Midland, Nepal Himalaya, since the Last Glacial Age is characterized by catastrophic topographic change such as deepening and filling by detritus occurred alternately. Highest terrace in the study area are distributed at the relative height of 100-150m from the present river bed and are formed by detritus derived from the Great Himalayan side. And they were dated back to 20-30ka by OSL method. Middle terrace formed by debris flow deposits is dated back to 4ka. Such detritus were derived from Great Himalaya as sudden breach of landslide dams. Trace of the long traveled debris flows implies catastrophic disaster might occur due to climatic and seismic events in near future.

Free Research Field

自然地理学

Academic Significance and Societal Importance of the Research Achievements

起伏が急変するネパール・大ヒマラヤ山麓部の河谷では，過去数万年から数千年の時間オーダーで年間6ー12mm程度の下刻が起こり，それに伴われて斜面の重力性変形も進んできた．その結果，10億立方mクラスの地すべり・山体崩壊が発生したり，地すべりに伴う岩屑が土石流として下流側に流入し河谷を埋積してきた．このような急速な下刻・埋積のサイクルは最終氷期後半以降少なくとも2回発生したことを明らかにしたことは学術的な意義がある．さらに，厚さ40m以上の土石流が30-40kmに亘って長距離流下することを明らかにしたことは，今後のハザードマップの作成に貢献できる．