ヒマラヤの氷河湖の水温構造再現 −イムジャ氷河湖を対象として−

Abstract

ヒマラヤでは氷河湖の拡大が大きな問題になっている。氷河湖の拡大は, 湖水に接する氷崖の底部が融解し, 氷崖上部の重さを支えきれず崩落することにより発生する。その為, 湖の水温構造を明らかにする事が重要であるが, 観測することは困難である。そこで三次元流動解析モジュール"Imja-3D"に, 仮定したImja湖周辺の2008年の気象条件を入力し, 水温構造の再現を試みた。計算の結果, 1997年に観測された水温構造と同様に表層付近に温度躍層が現れ, 中間層から低層では広く2-3度の温度層が再現された。

A glacier lake expansion is significant issue in Himalayan countries. A glacier lake expansion is due to glacier melting and ice cliff curving. An ice cliff calving is one of a glacier melting process underwater part of a glacier lake. Melting speed of underwater part is faster than above water surface part due to warm water in a glacier lake. Then the above part breaks up caused by unstable weight balance. This study aims to reproduce the water temperature structure in the Imja glacial lake using the 3D-Hydrodynamic model "Imja-3D" and the hypothetic meteorological datasets at the Imja glacial lake. The one-year datasets of hourly average air temperature were hypothesized using the temperature datasets at Namche Bazaar in 2008. The datasets of the wind speeds and the wind directions were considered diurnal pattern of the regional climate features in the Solukhumbu region. The model reproduced the water temperature structure of the lake in July 2008. The thermocline appeared near the lake water surface. The water temperature (2-3 degree) distribution was shown in mid layer. These results showed the similar water temperature structure on the observed one in the Imja glacial lake in 1997.