Study of thermal properties of supraglacial debris and degree-day factors on Lirung Glacier, Nepal

摘要

The extensive debris that covers glaciers in the ablation zone of the Himalayan region plays an important part in regulating ablation rates and water availability for the downstream region.The melt rate of ice is determined by the amount of heat conducted through debris material lying over the ice.This study presents the vertical temperature gradients,thermal properties in terms of thermal diffusivity and thermal conductivity,and positive degree-day factors for the debris-covered portion of Lirung Glacier in Langtang Valley,Nepal Himalaya using field-based measurements from three different seasons.Field measurements include debris temperatures at different debris thicknesses,air temperature,and ice melt during the monsoon (2013),winter (20 l 3),and pre-monsoon (2014) seasons.We used a thermal equation to estimate thermal diffusivity and thermal conductivity,and degree-day factors (DDF) were calculated from cumulative positive temperature and ice melt of the measurement period.Our analysis of debris temperature profiles at different depths of debris show the daily linear gradients of-20.81 °C/m,4.05 °C/m,and-7.79 °C/m in the monsoon,winter,and pre-monsoon seasons,respectively.The values of thermal diffusivity and thermal conductivity in the monsoon season were 10 times greater than in the winter season.The large difference in these values is attributed to surface temperature and moisture content within the debris.Similarly,we found higher values of DDFs at thinner debris for the pre-monsoon season than in the monsoon season although we observed less melting during the pre-monsoon season.This is attributed to higher cumulative temperature during the monsoon season than in the pre-monsoon season.Our study advances our understanding of heat conductivity through debris material in different seasons,which supports estimating ice melt and discharge from glacierized river basins with debris-covered glaciers in the Himalayan region.