Basic biology, Faculty of Bioscience and Biotechnology, (c/o Faculty of Science), Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8551, Japan. E-mail: ntakeuch@bio.titech.ac.jp Fax:81-3-5734-2946
Institute for Hydrospheric-Atmospheric Sciences, Nagoya University, Nagoya 464-8601, Japan. E-mail: nakawo@ihas.nagoya-u.ac.jp Fax:81-45-789-3436
Abstract:
In Himalayan region there are many debris covered glaciers with rock debris covering the ablation area. The debris area has complex surface morphologies such as supraglacial lakes, debris-covered cones, large hollows, ice cliffs and streams. It was pointed out that supraglacial lakes and ice cliffs probably play important role in complicated melting process at the debris covered area of this type of glaciers. In addition, recently, in many part of the Himalayan region, some supraglacial lakes rapidly expanded and outbursted. The big floods caused by these outbursts (glacier lake outburst flood, GLOF) destroyed inhabitants and natural environment downstream. Therefore, it is important to know the basic characteristics of the supraglacial lakes of this region. However, studies on these supraglacial lakes were still very few because the debris is usually unstable and it is sometimes very dangerous to carry out field investigation there. In this study we analyzed characteristics of supraglacial lakes on the debris covered area of a Himalayan glacier (Lirung glacier, Langtang region, Central Nepal).
28 lakes of various size were observed on the glacier. Turbidity,
electrical conductivity (EC), pH and temperature of the surface water varied
with the lake: Turbidity 0-364 mg/l , EC 9.0 - 45.8 µS/cm, pH 6.8 - 8.1
and water temperature 0.4 - 11.6 ûC. Pattern of water level change recorded
at 9 lakes could be divided into three types: Type 1) diurnal water level
change with a peak at the early afternoon, Type 2) diurnal water level change
with a peak in the evening, Type 3) no diurnal change. The lakes of Type
1 and Type 2 had lake water with high turbidity (more than 30 mg/l) and
low water temperature (less than 3 ûC) and the Type 3 lakes had water with
low turbidity (less than 5 mg/l) and high water temperature (4.7 -11.6 ûC).
The results and other observations strongly suggest that cold and highly
turbid melt-water flow into the Type 1 lakes mainly from the ice cliffs
around them and Type 2 lakes mainly from the englacial water system. Since
lake-water turbidity can be recognized as lake-water coloration in aerial
photographs and satellite images, turbidity of the supraglacial lakes could
be an indicator of glacier melting and debris thickness of this type of
glacier.