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Abstract
In Kyrgyzstan, outburst flood disasters from glacial lakes are increasing. An example is the sudden drainage on 8 August 2019 of the Toguz-Bulak glacial lake in the Tosor river basin of the northern Tien Shan region. In this study, we used remote sensing and field surveys to examine the reasons for the outburst. We found that the lake area changed from 0.021 km² to 0.002 km2 due to the outburst, in which most of the initial 130,000 m3 of water discharged within four hours. In examining the longer-term behavior of this lake, we found that from 2010 through 2019, it appears in June and disappears in September every year. Its maximum area occurs in late July and early August. With the expansion of the lake basin between 2010 and 2019, the lake also increased greatly in size, particularly so in the three years before the outburst, linked to high summer temperatures and the resulting higher inflow of glacier meltwater, finally leading to the sudden drainage in 2019. Before this outburst, a 2-m high moraine dam retained the lake. Continuously inflowing meltwater and the related increasing pressure by the lake water mass eventually broke the moraine dam. Satellite radar interferometry revealed active displacement fringes in the lake basin and moraine dam due to the melting and subsidence of buried ice. An analysis using digital elevation models from 1964 and 2010 also confirms the surface lowering in the lake basin by up to 8.5 m and on the moraine dam by 2 m. Such lowering of the proglacial moraine complex destabilized the moraine dam.
Highlights
A warming climate continues to degrade glaciers in high mountains, producing numerous new glacial lakes with their associated outbursts every year [1,2,3,4]
The Himalayas [5] and the Andes [6] have the most frequent glacial lake outburst floods (GLOFs) that result in severe damage and casualties [7,8]
In the summer of 2019, the lake area increased as in other years but became significantly larger than that in the previous years.On about 5 July 2019, the glacial lake appeared in the lake basin (Figure 2a) and steadily increased in size (Figure 3)
Summary
A warming climate continues to degrade glaciers in high mountains, producing numerous new glacial lakes with their associated outbursts every year [1,2,3,4]. The Himalayas [5] and the Andes [6] have the most frequent glacial lake outburst floods (GLOFs) that result in severe damage and casualties [7,8] These floods arise when a moraine-dammed lake has a dam failure due to an overtopping wave induced by mass movements, ice falls, ice and snow avalanches or rock-slope failure upslope from the dam [9,10], and/or piping [11] and ice-cored degradation [12] of the dam. (b) The breached dam region the day Background orange profile from Corona KH-4A/DSM for 1964. The moraine dam resisted for two days, on 6 th and 7 th August, better understand the changes around the lake basin, we used DInSAR interferograms to andTo failed (Figure 2b,c). 2016 and 30 October 2016 and between 11 June 2017 and 17 September
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