ИСТИНА

Sediment cores were collected from three alpine lakes in the Central Caucasus: Donguz-Orun in 2016, Syltrankol in 2022,and Bashkara in 2023. The collected sediment cores were subjected to a comprehensive analysis process, which included visual inspections, analysis of their grain-size and mineral composition, and measurement of natural (210Pb and 226Ra) and artificial (137Cs and 241Am) fallout radionuclide concentrations using gamma-ray spectrometry. The data obtained was valuable for understanding changes in sediment load trapped in lakes during the deglaciation. Chosen water bodies in the Elbrus region are the largest alpine lakes, with different origins and varying levels of ice cover within their catchment areas. Although snow and ice melt water are the major contributor to their water balance. Doguz Orun Lake (2544 m ASL) was formed as a result of the sub-damming of glacier of the same name. It is fed by runoff from two separate catchments that form an inner delta near the lake. It has been revealed that during the post-Chernobyl period, sedimentation rates significantly increased. However, this cannot be directly attributed to the degradation of ice cover, due to the complexity of the sediment delivery pathways involved. Syltrankol Lake (3197 m ASL) is located in a glacial cirque that lost most of its ice cover during the 19th and 20th centuries, as documented by various sources which turned out to be in a good agreement sediment core study. As well deglaciation was accompanied by an outburst flood in 1881, caused by the collapse of ice. Bashkara Lake (2573 m ASL) is the youngest of all the lakes. It formed as a supraglacial lake in the first half of the 20th century and has grown along with the retreat of the glacier. Today, it is a proglacial lake whose banks consist of a moraine ridge and the edge of the glacier. After melting of ice dam resulted into outburst on September 1, 2017 the depth dropped almost in two times from more than 30 to 17 m. Radioisotope dating revealed that more than one meter of strata accumulated in less than 50 years. This high rate of sedimentation could lead to the rapid filling of the lake's hollow and the risk of new flooding.