Features of the Dynamics of Bezengi and Bashkara Glaciers with a Debris Cover in the Central Caucasus

Based on the analysis of satellite images and aerial photography, the study revealed the formation of a debris cover of mudflow and landslide deposits on the surface of the Bezengi Glacier in 2016–2018 and the Bashkara glacier in 2019 in the Central Caucasus. It was found that while the main part the Bezengi glacier tongue was retreating, its right part under the debris cover continued to move forward and, in addition, began to shift to the left to the centerline. The right part of the glacier, which accelerated the movement, began to deform the proluvial/colluvial fan on the slope of the lateral moraine on a distance longer 600 m, with the formation of cracks and falls of the debris mass to the foot of the slope. The source of the Cherek-Bezengiysky River has shifted from the left side of the glacier to the right side and down the valley for a distance of 280 m in the period 2022–2024. As a result of the involvement of dead ice mass in the movement, in 2024 the Bezengi glacier terminus was at the same place that it was in 2014. After the snow-ice-rock avalanche on the surface of the Bashkara Glacier, the dynamics of its right flow changed. Below it there is a significant frontal mass of dead ice, which is not capable of engaging in motion. Therefore, the ice flow began to shift to the left, affecting the main left ice flow. As a result, in 2024, there was a change in the direction of the subglacial channel of meltwater runoff, the main part of which flowed towards Lake Bashkara, increasing its water inflow. This in the debris flow release into the lake and then to a change in the channel on the dam-break section below the Bashkara Lake with partial undercutting of its slopes. Due to that a threat of erosion of the bottom of the dam-break and a new outburst of the Bashkara Lake became quite probable. The events of 2024 in the areas of the terminus parts of the Bezengi and Bashkara glaciers showed that against the background of the ongoing degradation of glaciers, extraordinary events are still possible being caused by the restructuring of the subglacial drainage system in several years after the formation of a debris cover on the glaciers due to rock avalanches or debris flows.

Bezengi Glacier, rock avalanche, debris flow, Bashkara Lake, debris cover, glacier advance, subglacial channel