The 24 July 2008 outburst flood at the western Zyndan glacier lake and recent regional changes in glacier lakes of the Teskey Ala-Too range,

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During 2006-2014 in the western Teskey Range, Kyrgyzstan, four large drainages from glacial lakes have occurred. These flooding events caused extensive damage, killing people and livestock as well as destroying bridges, roads, homes, and crops. According to satellite data analysis and field surveys, the volume of water that drained at Kashkasuu glacial lake in 2006 was 143,900 m 3 , that at Jeruy lake in 2013 was 173,300 m 3 , and that at Karateke lake in 2014 was 131,000 m 3. Due to their tunnel outlet, we refer here to these glacial lakes as a "tunnel-type" of short-lived glacier-lakes that drastically grow and drain over several months. From spring to early summer, such a lake either appears, or in some cases, significantly expands from an existing lake, and then drains during summer. Our field surveys show that these short-lived lakes form when the ice tunnels inside a debris landform get blocked. The blocking is caused either by the freezing of stored water during winter or from collapse of the ice tunnel. The draining occurs through an open ice tunnel during summer. The growth-drain cycle can repeat when the ice-tunnel closure behaves like that on supraglacial lakes on debris-covered glacier. We argue here that the geomorphological conditions in which such a short-lived glacier lake appears are (i) existence of a debris-landform (moraine complex) with dead ice, (ii) existence of lake-basin depressions having its water supply 2 on a debris-landform, and (iii) no surface water channel from lake-basin depressions. Using these geomorphological conditions, we examined 63 lake-basin depressions (> 0.01 km 2) in this region and identify here 50 of them that are potential locations for a short-lived glacial lake. 1. Introduction The northern Tien Shan in Kyrgyzstan, Central Asia contains many small glacial lakes at glacier fronts (Narama et al., 2015). These lakes are of limited size, with areal extents of 0.001-0.05 km 2 compared to the large proglacial lakes in the eastern Himalayas that exceed 0.1 km 2 (Komori et al., 2004). Nevertheless, in recent decades, rapid drainage from such lakes in the Central Asian Mountains have caused severe damage for residents in nearby mountain villages (Kubrushko and Staviskiy, 1978;

To assess the current state of glacial lakes, we examine the seasonal lake-area changes of 339 glacial lakes in the Teskey and Kungoy Ranges of the Issyk-Kul Basin, Kyrgyzstan, during 2013-2016 based on optical satellite images (Landsat7/ETM+ and 8/OLI). The glacial lakes are classified into six types based on their seasonal variations in area: stable, increasing, decreasing, appearing, vanishing, and short-lived. We then track the number of each type in a given year and examine how each number changes from one year to the next. We find that many appearing, vanishing, and short-lived types occurred in both mountain ranges, having a large variability in number that is not directly related to the local short-term summer temperature anomaly, nor to precipitation or glacier recession. However, those in the Teskey Range vary significantly more than those in the Kungoy Range. To determine if the changing number and distribution of the various lake types may be due to changes in ground ice, we apply differential interferometric synthetic aperture radar (DInSAR) analysis using ALOS-2/PALSAR-2 for the debris landforms behind which glacial lakes appear. In the Teskey Range, ground ice occurs in 416 out of a total of 557 debris landforms, whereas in the Kungoy Range, ground ice occurs in 71 out of 131. In zones with predominant glacier-retreat during 1971-2010 (from Corona KH-4B and ALOS/PRISM), the Teskey Range had 180 new lake depressions as potential lake-basins, whereas the Kungoy Range had just 22. Existing depressions also expanded when melting ice produced subsidence. Such subsidence, together with debris landforms containing ground ice and ice tunnels, appear to cause the observed large number variability. In particular, the deposition of ice and debris by tunnel collapse or the freezing of storage water in a debris landform may close-off an ice tunnel, causing a lake to appear. Subsequent reopening via melting of such blockage would produce either a vanishing or a short-lived type. In this way, the large variability in the number of each lake type and the distribution of types over this four-year period arises from regional geomorphological conditions and not directly from the local short-term summer temperature anomaly and precipitation or glacier recession.

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