The Change Of Glacial Lake And Its Influence In The Everest Region

In the context of global warming,the majority of glaciers have experienced accelerated reduction,promoting glacial lake outburst floods(GLOFs).Changes of glacial lakes and their causes,and the stability of Longbasaba Lake(potentially potential dangerous glacial lakes,PDGLs)moraine dam were examined and assessed in the Everest region,based on Landsat TM/ETM+/OLI images and field observations data.A total of 1467 glacial lakes with overall area 128.99±14.17 km~2 were inventoried in 2015.The area of glacial lakes expanded at average rate of +0.98%/a over the past 25 years.This change resulted from an observable temperature increase and glacier shrinking.While small– to medium–sized(<0.5km~2)varied more drastically;Ice–contacting lakes responded most sensitively to glacier change,and grew fastest with increase rate +2.02%/a were direct signals of climate warming and glacier meltwater increase;About 25.12 km~2 net lake area increment,which accounted for about 87.2% of the total net glacial lake area,were contributed from the bands of 4800~5400 m with a maximum value of 6.84 km~2 in 5100~5200m.The discrepant change rates of glacial lake in different elevation bands may indicate differential glacier melting responses to climate change.Furthermore,the 58 PDGLs can be further rated as 29 glacial lakes(29.80 km~2)with high breaching probabilities,12 lakes(9.46 km~2)with mid–level breaching probabilities and 17(5.65 km~2)with low breaching probabilities.Thermal and hydrological dynamics and their impacts on stability of a moraine dam were analyzed and simulated for Longbasaba Lake in the Himalayas,based on soil temperature,moisture,and heat flux data at different depths in the dam from 2012 to 2015.The simulation indicates that the average yearly maximum thawing depth has been ~0.3 m deeper than the average yearly maximum freezing depth during the observation period.During the1960~2015,yearly maximum thawing depth has increased,while yearly maximum freezing depth has decreased,implying that permafrost in the dam has been deteriorating.The annual surplus heat and increasing permafrost thawing depth will result in further deterioration of permafrost and melting of buried ice in the dam,thereby decreasing its stability.