ИСТИНА

In the Caucasus, there have been reported and documented seven recent moraine failures. Such events are common for highly unstable proglacial areas. Here we present a detailed reconstruction of the moraine failure in the Djankuat valley in the Central Caucasus. We then analyze the subsequent terrain dynamics of the breach and its surroundings. The event occurred on 1st July 2015 and led to the alteration of the Koyavgan creek stream. Koyavgan creek is the largest tributary of the Djankuat River that emerges from the small <0.5 km2 glacier in the cirque and further conjoins the stream from another small glacier Via-Tau. The total area of the watershed above the breach is 3.03 km2 . Primarily the collapse was caused by intensive precipitation: 227 mm during the seven preceding days. During the weekly period, the surface runoff was significantly increased due to the relatively large drainage area. It disintegrated the internal moraine sediments and led to a collapse. The buried ice underlying the moraine ridge had a crucial role in the event. The investigated section of the moraine on 60 m width was lying below the adjacent moraine edges before the event due to degradation of the ice core. To accomplish the established goal, we use satellite imagery in combination with repeated UAV surveys. Based on high-resolution stereo images we construct DEMs with a spatial resolution of 1 m to estimate the event. Since 2019 we have accomplished UAV monitoring: currently, five surveys have been conducted. Followingly, we obtained high-resolution DEMs with spatial resolution varying in diapason 4.7-9.5 cm. We divided the area into several zones: the breach, the area of regressive erosion, the accumulative cone, and two sides of the adjacent lateral moraine. Finally, we conducted a quantitative analysis of the terrain dynamics for these sections.