Formation, evolution, and drainage of short-lived glacial lakes in permafrost environments of the northern Teskey Range, Central Asia

摘要

In the Teskey Range of the Tien Shan (Kyrgyz Republic),fiveoutburst flood disasters from short-lived glacial lakes in 2006, 2008, 2013, 2014, and 2019 caused severe damages in the downstream part. Short-lived glaciallakes in the Teskey Range grow rapidly and drain within a few months, due toclosure and opening of an outlet ice tunnel in an ice-cored moraine complexat the glacier front. In addition to these factors, summer meltwater fromthe glacier can cause rapid growth. Outburst floods of this lake type are amajor hazard in this region and differ from the moraine-dam failures commonto the eastern Himalaya. To clarify how short-lived glacial lakes store anddrain water over short periods, we use results from a field survey andsatellite data to analyze the water level, area, volume, and discharge of Korumdu lake (2017–2019) as well as satellite data to monitor theappearance of 160 other short-lived lakes (2013–2018). Except in 2016,Korumdu lake appeared and drained within about 1?month during all thesummers. Water level data recorded by a data logger and time-lapse cameraimages show that the lake appeared and expanded suddenly from July to Augustin 2017–2019. The timing of lake appearance indicates that the lake formedwhen an outlet ice tunnel (subsurface channel) drainage was blocked bydepositions of an ice–debris mixture due to ice melting and not by freezing ofstored water. For 2017, we used uncrewed aerial vehicle (UAV)-deriveddigital surface models (DSMs) and water levels, finding that the lake'svolume reached 234?000?m3 within 29?d, and then the water dischargedfor 17?d at a maximum rate of 0.66?m3/s. This discharge rate is morethan 20 times smaller than those found earlier (2006–2014) for fourshort-lived lakes of tunnel type in this region. We argue that this large variation indischarge rates is due to variation in the dimensions of the outletice tunnels. For the 160 other short-lived glacial lakes, we found that 117formed during the ice-melt period from July to September. This timing andour findings for Korumdu lake show that these 117 lakes likely formedprimarily because deposition of an ice–debris mixture blocked the outlettunnel, though increased glacial melt would also have contributed. In theTeskey Range, the appearance of short-lived glacial lakes on the morainecomplexes at glacier fronts is inevitable in summer when the melting rate ishigh. Similar behavior of short-lived lakes may occur in other mountainregions of Central Asia, such as the Tien Shan and Pamir Mountains, whereverice-cored moraine complexes exist within mountain permafrost zone. Moreover,increasing temperatures may increase both tunnel size and lake-basin size(lake volume), leading to increased hazard potential from such lakes in thefuture.