Modeling Sub-Debris Melt at Lirung Glacier, Langtang Valley, Nepal Himalayas

Abstract:

Glaciers are key resources of water for hydropower, irrigation, and drinking water. The extensive debris cover often covers glaciers in ablation part of the Himalayan region; hence, it is essential to assess the effect of debris on glacier ice melt. In this study, the main objective is to estimate the sub-debris melt using debris temperature at Lirung Glacier of Nepal Himalayas. Three field campaigns are carried out in monsoon (2013), winter (2013) and pre-monsoon (2014) season during which 2 set of thermistors are installed at different debris thickness. Debris temperature data are collected in different layers of debris from atmosphere/debris interface to debris/ice interface using temperature sensors during each season. Surface temperature for monsoon season is calculated from meteorological data measured at Glacier. Ice melting under debris is calculated for three different seasons and found highest during monsoon season and lowest during winter season. Similarly, seasonal vertical temperature gradients are calculated and vertical debris temperature profiles are generated. The daily linear gradient of the vertical debris temperature profile with depth are -21.38, 1.81, -10.53 ^oC m^–1 in monsoon, winter, and pre-monsoon seasons, respectively. Based on the measured daily ice melt in monsoon, winter and pre-monsoon, positive degree-day factors are estimated for Lirung debris-covered Glacier. Similarly, the debris temperature profile shows higher fluctuation of temperature near surface and lower fluctuation in lower layers with increasing lag time. This study is useful to understand the melting patterns of debris covered glaciers in different seasons, which will be helpful to estimate water availability from glacierized river basins with debris-covered glaciers in the Himalayan region.