Large drainages from short-lived glacial lakes in the Teskey Range, Tien Shan Mountains, Central Asia

Four large drainages from glacial lakes occurred during 2006–2014 in the western Teskey Range, Kyrgyzstan. These floods caused extensive damage, killing people and livestock as well as destroying property and crops. Using satellite data analysis and field surveys of this area, we find that the water volume that drained at Kashkasuu glacial lake in 2006 was 194 000 m3, at western Zyndan lake in 2008 was 437 000 m3, at Jeruy lake in 2013 was 182 000 m3, and at Karateke lake in 2014 was 123 000 m3. Due to their subsurface outlet, we refer to these short-lived glacial lakes as the “tunnel-type”, a type that drastically grows and drains over a few months. From spring to early summer, these lakes either appear, or in some cases, significantly expand from an existing lake (but non-stationary), and then drain during summer. Our field surveys show that the short-lived lakes form when an ice tunnel through a debris landform gets blocked. The blocking is caused either by the freezing of stored water inside the tunnel during winter or by the collapse of ice and debris around the ice tunnel. The draining then occurs through an opened ice tunnel during summer. The growth–drain cycle can repeat when the ice-tunnel closure behaves like that of typical supraglacial lakes on debris-covered glaciers. We argue here that the geomorphological characteristics under which such short-lived glacial lakes appear are (i) a debris landform containing ice (ice-cored moraine complex), (ii) a depression with water supply on a debris landform as a potential lake basin, and (iii) no visible surface outflow channel from the depression, indicating the existence of an ice tunnel. Applying these characteristics, we examine 60 depressions (> 0.01 km2) in the study region and identify here 53 of them that may become short-lived glacial lakes, with 34 of these having a potential drainage exceeding 10 m3 s−1 at peak discharge.


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The population and villages are distributed over the northern part of the Teskey

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Range. There, villagers use the large alluvial fans at the mountain piedmont as pasturage 114 or agricultural fields.    Range directly contacts a glacier, so we call it a "glacier-contact" type. In

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The lake, which has glacier contact, drains on 15 August 2013, but some water remains 185 on 23 September.

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Nearby and to the east lies Karateke lake. This lake is without glacier contact 187 and located on a debris-landform at the glacier front. Figure 3C shows the lake area to  We observed exposed ice and ice tunnels on similar debris-landforms in front 216 of the Jeruy and Karateke Glaciers (Fig. 5A, B). Both debris-landforms contain buried 217 ice. Jeruy lake appeared on the depression of a basin with glacier contact. Karateke lake 218 also formed at an empty depression, but without glacier contact. For the Karateke lake, 219 meltwater from the glacier terminus flows into the depression. But for the outlets of 220 both lakes, we observed no visible surface outflow channel from either depression.  Our field survey thus indicates that lake water from the Kashkasuu, Jeruy, and 226 Karateke lakes discharged through ice tunnels inside of debris-landforms, as was found 227 previously also for the western Zyndan lake (Narama et al., 2010a). In these 228 debris-landforms, there are no visible surface outflow channels, and most meltwater 229 from the glacier flows through an ice tunnel. Hence, we consider these short-lived 230 glacial lakes as "tunnel-type" to distinguish them from those that discharge through 231 different mechanisms (e.g., dam failure, surface channel blockage).    (Fig. 8). Of the 60 depressions, 38 (i.e., 63%) of the depressions had glacier 288 contact in which meltwater can inflow from glacier termini.

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The depressions without glacier contact are of the "water accumulation" and 290 "non-accumulation" types. The depressions of water accumulation type can get 291 meltwater from the glacier because the depression is connected to it via one or more 292 subsurface channels. In contrast, the non-accumulation type is not connected to a water 293 channel and cannot get substantial amounts of water within short time. We found 22 294 depressions of the water accumulation type, and each may become a short-lived lake 295 such as the Karateke lake (Fig. 3C). In addition, we determined whether or not the 296 depression had a surface outflow channel. Among the 60 depressions, 7 depressions had 297 a surface outflow channel and thus cannot hold a short-lived lake of the tunnel-type 298 studied here.

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The relationship between area and volume of the 10 measured lakes agrees 300 with those found previously. In the plot of Fig. 9, we also show the four large drainages

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In contrast, the short-lived glacial lake type studied here appears and expands 345 for a few months, and then discharges through ice tunnels. The lake appears in a 346 depression that develops after recent glacier recession (Narama et al., 2010a). After 347 drainage, vertical subsidence occurs along the subsurface channel in the debris landform.

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Such a short-lived glacial lake type recurs when its ice tunnel closes, similar to that on a 349 supraglacial lake on a glacier or on a debris-covered glacier (Kropáček, et 359 In addition to monitoring existing lakes, our findings suggest that one should 360 also monitor empty depressions in which a short-lived glacial lake may form. But which 361 depressions should be monitored? We can rule out some depressions by examining 362 several features of the depression and its environment as follows.

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One characteristics to rule out some cases is not having a clear source of 364 meltwater. That is, a short-lived glacial lake cannot appear at a depression in which 365 meltwater cannot inflow at substantial amounts. Among the 60 depressions (> 0.01 km 2 ) 366 we examined, 38 of them had glacier contact and thus can get meltwater directly from 367 glacier termini. The remaining 22 depressions had no glacier contact, but could also 368 accumulate water type such as the Karateke lake (Fig. 3C). As another 369 geomorphological feature to rule out potential hazardous cases, in the case of the basin 370 has outflow channels, a short-lived lake cannot storage much water for a short term. We  but Jeruy's debris-flow type was a viscous flow with matrix-supported deposits (Fig. 408 6A), whereas Karateke's was a stony debris-flow with clast-supported deposits (Fig. 6B).

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To help us understand these differences, we also investigated the debris flows that  Observations show that entrainment make debris flows more and more erosive, 421 resulting in a feedback effect (Breien et al., 2008). This effect partly explains the high 422 rate of volume increase observed in many debris flows and is probably often necessary 423 to achieve long runouts in subaerial flows. 424 We characterize potential flows by the erodible channel distance and the 425 estimated maximum discharge. We estimate here the maximum discharge of 60 426 depressions and existing lakes using the duration of discharge and Q max = 46(V/10 6 ) 0.66 427 (tunnel event; Walder and Costa, 1996), with a water volume V. This formula neglects 428 the possible role of tunnel size in total drainage volume. For an existing lake, V is 429 estimated using the regression formula in Fig. 9. In the study area, the erodible channel 430 distances range between 166 and 6016 m, and the maximum slope gradients of the mean 431 erodible channel distance are 11.5-20.9°. We also characterize actual drainage events 432 (the above four recent floods) using these two parameters. 433 The results, plotted in Fig. 10  changes. The applicability of Sentinel-1 radar data (6 days repeat) for monitoring these 497 lakes remains to be tested (Strozzi et al., 2012). For such systematic surveillance, the 498 type of prioritization of potentially dangerous sites as proposed here is essential. We 499 propose an early information network based on monitoring with satellite data that 500 informs the responsible authorities and possibly local people when a lake appears. As In the Tien Shan, depressions (> 0.01 km 2 ) in which water can inflow should be 505 monitored, just as we now monitor glacial lakes, and their potential associated hazards 506 considered. Lake monitoring using satellite data should proceed based on the criteria of 507 potential dangerous lakes outlined here such as the location and volume of the lakes and 508 depressions, the flood type, and landform on the mountain pediment.