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近年, 南アジアのヒマラヤ地域やその他の氷河地帯で, 気候変動と氷河の後退に起因する大きな災害が発生している。気候変動の影響で氷河湖は急速に発達・拡大しており, 決壊の危険性が指摘されている。氷河湖の決壊は下流域に壊滅的な洪水や災害をもたらす。したがって, 気候変動が氷河湖に与える影響を調査し, 氷河湖の挙動を把握することが不可欠である。本研究は, ネパール・ヒマラヤのツォ・ロルパ氷河湖での現地調査について報告するとともに, 気候変動がツォ・ロルパ氷河湖にもたらす影響について検証を行うものである。ツォ・ロルパ氷河湖はネパールで最も大きく, 潜在的危険性の最も高い氷河湖である。浸水・越流によるモレーンダムの決壊が引き起こす氷河湖決壊についての数値解析モデルを構築し, その解析結果を実験により得られた結果と比較した。, In recent years climate change and retreating glaciers constitute a major hazard in the Himalaya of South Asia or glacier regions of the world. Glacial lakes are rapidly developing or increasing due to climate change, which may cause the outburst of the lake. The outburst discharge from the glacial lake can cause catastrophic flooding and disasters in downstream area. Therefore, it is necessary to investigate the impact of climate change on glacial lakes and to understand the behavior of the glacial lakes. In this study, the field assessment of Tsho Rolpa Glacial Lake in the Himalaya of Nepal has been presented and the impact of climate change on this glacial lake has been discussed. The Tsho Rolpa Glacial Lake is the largest and most potentially dangerous glacial lake in Nepal. A numerical model has been also developed for computing the characteristics of glacial lake outburst due to moraine dam failure by seepage and water overtopping. The simulated results are compared with the experimental results.

気候変動に起因する氷河湖決壊洪水(GLOF)による洪水災害と土砂災害は南アジアのヒマラヤ地域やその他の氷河地帯においてたびたび発生し、下流において深刻な洪水災害をもたらす脅威となっている。氷河湖の決壊の主な原因は、氷塊の移動が急激な水位上昇や浸透流、氷河サージを引き起こし、それによってモレーンダムが破壊されることである。本報は、モレーンダムの破壊に起因する氷河湖決壊を研究したものである。浸透流と水位上昇による越流がもたらすモレーンダム破壊を一連の実験によって検証し、浸透とモレーンダムの破壊について行った数値解析結果と比較した。また、氷河湖に与える全球気候変化の影響も解析し、観測記録にもとづいて氷河湖決壊洪水流量を予測する経験的関係を導いた。, Due to impact of climate change flood and sediment disasters caused by Glacial Lake Outburst Flood (GLOF) are frequently occurred in the Himalaya of South Asia or glacier regions of the world. GLOF poses a serious threat of flood disasters at downstream valley. Outburst of glacial lakes typically occurs due to moraine dam failure caused by glacier mass movement leading to a rapid rise of water level, seepage flow and a surge. The outburst of glacial lake due to moraine dam failure has been investigated. The moraine dam failure by seepage flow and overtopping due to water level rising has been investigated though a series of flume experiments. Numerical analysis of seepage and moraine dam failure has been also performed. The simulated results are compared with the experimental results. The impact of global climate change on glacial lakes is also analyzed. The empirical relationship to predict GLOF discharge has been also developed based on the recorded GLOFs discharge.