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

Abstract

In the Teskey Range of the Tien Shan (Kyrgyz Republic), five outburst flood disasters from short-lived glacial lakes in 2006, 2008, 2013, 2014, and 2019 caused severe damages in the downstream part. Short-lived glacial lakes in the Teskey Range grow rapidly and drain within a few months, due to closure and opening of an outlet ice tunnel in an ice-cored moraine complex at the glacier front. In addition to these factors, summer meltwater from the glacier can cause rapid growth. Outburst floods of this lake type are a major hazard in this region and differ from the moraine-dam failures common to the eastern Himalaya. To clarify how short-lived glacial lakes store and drain water over short periods, we use results from a field survey and satellite data to analyze the water level, area, volume, and discharge of Korumdu lake (2017–2019) as well as satellite data to monitor the appearance of 160 other short-lived lakes (2013–2018). Except in 2016, Korumdu lake appeared and drained within about 1 month during all the summers. Water level data recorded by a data logger and time-lapse camera images show that the lake appeared and expanded suddenly from July to August in 2017–2019. The timing of lake appearance indicates that the lake formed when an outlet ice tunnel (subsurface channel) drainage was blocked by depositions of an ice–debris mixture due to ice melting and not by freezing of stored water. For 2017, we used uncrewed aerial vehicle (UAV)-derived digital surface models (DSMs) and water levels, finding that the lake's volume reached 234 000 m3 within 29 d, and then the water discharged for 17 d at a maximum rate of 0.66 m3/s. This discharge rate is more than 20 times smaller than those found earlier (2006–2014) for four short-lived lakes of tunnel type in this region. We argue that this large variation in discharge rates is due to variation in the dimensions of the outlet ice tunnels. For the 160 other short-lived glacial lakes, we found that 117 formed during the ice-melt period from July to September. This timing and our findings for Korumdu lake show that these 117 lakes likely formed primarily because deposition of an ice–debris mixture blocked the outlet tunnel, though increased glacial melt would also have contributed. In the Teskey Range, the appearance of short-lived glacial lakes on the moraine complexes at glacier fronts is inevitable in summer when the melting rate is high. Similar behavior of short-lived lakes may occur in other mountain regions of Central Asia, such as the Tien Shan and Pamir Mountains, wherever ice-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 the future.