The study aims to reconstruct the Altai glaciers at the maximum of the LIA, to estimate the reduction of the Altai glaciers from the LIA maximum to the present, and to analyze glacier reduction rates on the example of the Tavan Bogd mountain range. Research was based on remote sensing and field data. The recent glaciation in the southern part of the Altai is estimated (1256 glaciers with the total area of 559.15 ± 31.13 km²), the area of the glaciers of the whole Altai mountains is estimated at 1096.55 km². In the southern part of Altai, 2276 glaciers with a total area of 1348.43 ± 56.16 km² were reconstructed, and the first estimate of the LIA glacial area for the entire Altai mountain system was given (2288.04 km²). Since the LIA, the glaciers decrease by 59% in the southern part of Altai and by 47.9% for the whole Altai. The average increase in ELA in the southern part of Altai was 106 m. The larger increase of ELA in the relatively humid areas was probably caused by a decrease in precipitation. Glaciers in the Tavan Bogd glacial center degraded with higher rates after 1968 relative to the interval between 1850–1968. One of the intervals of fast glacier shrinkage in 2000–2010 was caused by a dry and warm interval between 1989 and 2004. However, the fast decrease in glaciers in 2000–2010 was mainly caused by the shrinkage or disappearance of the smaller glaciers, and large valley glaciers started a fast retreat after 2010. The study results present the first evaluation of the glacier recession of the entire Altai after the LIA maximum.

The glacier recession of the North-Chuya ridge, Altai, after the maximum of the Little Ice Age (LIA) is estimated based on remote sensing and in situ studies of the Bolshoi Maashei glacier. The glacier area decreased from 304.9 ± 23.49 km² at the LIA maximum to 140.24 ± 16.19 km² in 2000 and 120.02 ± 16.19 km² in 2021. The average equilibrium-line altitude (ELA) rise after the LIA was 207 m. The reduction of glaciers was caused by the warming trend, most rapid in the 1990s, and by the decrease in precipitation after the mid-1980s. The volume of glaciers decreased from approximately 16.5 km³ in the LIA maximum to 5.6–5.8 km³ by 2021. From the LIA maximum to 2022, the Bolshoi Maashei glacier decreased from 17.49 km² to 6.25 km², and the lower point rose from 2160 m to 2225 m. After the LIA, the glacial snout retreat was about 1 km. The fastest retreat of the glacier terminus was estimated in 2010–2022 as 14.0 m a⁻¹ on average. The glacier mass balance index was calculated, with the results showing a strong negative trend from the mid-1980s until now. Strong melt rates caused the increase in the area of the Maashei lake, which could lead to the weakening of its dam, and prepared for its failure in 2012. The current climatic tendencies are unfavorable for the glaciers.

There is a reduction in the area of glaciation of mountain massifs as a result of climate warming, which leads to the formation of lake-glacial complexes in areas of glaciation degradation. These complexes are dynamic systems that are rapidly changing over time, therefore, unstable and potentially outburst. Moraine and periglacial lakes outbursts are dangerous hydrological phenomena. As a result of outbursts catastrophic floods and mudflows can form, causing serious damage to the infrastructure of settlements located downstream and often leading to human toll. Therefore, the study of outburst-hazardous lakes is necessary and is an important applied problem associated with forecasting natural hazards. In this paper an the outburst hazard of little-studied moraine and periglacial lakes at the Mongun-Taiga mountain massif (Tyva Republic, Russian Federation) assessment was carried out using the scoring method, supplemented taking into account regional characteristics, using data from remote sensing of the Earth. The performed assessment according to satellite images showed that most of the massif's lakes have a high outburst hazard. Based on the assessment results a group of lakes was selected located in the right branch upstream of the river “Tolaity” for the purpose of a more detailed field survey (hydrological and geophysical studies were carried out). Field work carried out on the selected group of lakes allowed us to correct the performed assessment. In paper the applicability of the method based on comparing field data and data obtained from satellite images was estimated.

The retreat of mountain glaciers inevitably leads to an increase in the number of outburst moraine lakes. One of the possible mechanisms of moraine dam outburst along with overflow over the crest is the formation of a filtration channel in the body of the moraine dam (piping). An algorithm for calculating the outburst flood hydrograph, describing the development of a filtration channel in the body of a moraine dam and the subsequent formation of water overflow when the soil above the channel collapses, is proposed in this paper. Verification of proposed methodology was carried out on the basis of experimental data and published data of real outbursts. Satisfactory results verifying this methodology made it possible to use the proposed methodology for the calculation of the hydrograph of the outburst of Lake Bashkara in the Elbrus region, which occurred on 1 September 2017. It is shown that the simulation results are quantitatively comparable with the estimates obtained from field data: the time of water discharge through the channel was 16 min, the period of the outburst wave passage was 40 min, and the maximum discharge was 636 m³/s. Thus, the possibility of applying the proposed methodology for calculating the destruction of natural moraine dams has been demonstrated.

The destruction of ground dams, of natural and artificial origin, is caused by certain critical conditions. The main reasons for this are the overflow of water over the crest of a dam, the filtration of water through its body, or mechanical destruction. The processes of destruction of ground dams of moraine lakes are very frequent phenomena for mountain regions and can often occur there. In addition, the outburst of ground dams can take place under the thickness of the cover and mountain glaciers that leads to the formation of the subglacial hydrographic drainage system. Because of the dam destruction, outburst floods, which are accompanied by significant destruction and even human losses, are formed. Considering that, it is extremely difficult and unsafe to investigate the outburst process directly at the time of its natural occurrence, the researchers turn to alternative methods, like physical modeling. In this paper, the results of physical modeling of the outburst of the moraine model reservoir are presented. The experiment was carried out near the coastline of the outburst glacier lake Bashkara (Central Caucasus, Elbrus Region, Russia). Therefore, the artificial dam, consisting of material of moraines surrounding the lake, was created. This leads to a possibility to recreate the experimental conditions closest to natural. During the research photography and video filming of the outburst of the model reservoir were carried out. The results of physical modeling are in complete agreement with previously published data of outburst of ground dams and do not contradict with the physical essence of the process.