ヒマラヤのImja氷河湖周辺の現地観測結果

Abstract

ヒマラヤの高山域では, 氷河湖決壊洪水が大きな問題になっている。しかし多くの氷河湖では十分な気象観測が行われておらず, 氷河湖の水収支が明らかでない。そこで, 氷河湖の水収支モデルを開発する為に, ネパールのImja氷河湖周辺で気象観測を行った。観測の結果から, 気温と風速は類似した日周変化を示し, 日中の氷河上の風向は南南西から南西の風が卓越していた。氷河を覆うデブリ (土砂混じりの岩屑) のデブリ層中温度 は, デブリが厚くなるほど気温の変動を受けにくくなる結果が得られた。アルベドの観測では, デブリが混じった湖水のアルベドが, 氷河上のデブリのアルベドより低くなる結果が得られた。

The glacial lake outburst flood is a critical issue at the high mountain region of Himalaya. However, available meteorological observation data are still limited in clarifying the water budget mechanism of the glacial lake. This study has carried out field investigation around the Imja glacial lake in Nepal with the objective of development of a glacial lake hydrological model. The meteorological observation results showed that air temperature had strong relationship with wind speed. These results showed that, during the field observation period, averaged wind direction was south-west at the Imja glacier in the day time. The fluctuation of subsurface temperature of debris was influenced by the covered debris thickness. It was found that when the thickness of the debris exceeds 10 cm, the subsurface temperature of the debris kept at zero degree in the day time. The observation of albedo indicated that the albedo of glacial water was lower than that of the debris.