On 20 September 2002, an enormous rock/ice slide and subsequent mud-flow occurred on the northern slope of the Kazbek massif, Northern Ossetia, Russian Caucasus. It started on the northnortheast wall of Dzhimarai-Khokh (4780 m a.s.l.) and seriously affected the valley of Genaldon/Karmadon. Immediate governmental actions, available scientific information, first reconstructions, hazard assessments and monitoring activities as well as initial expert judgments/recommendations are documented in order to enable more detailed analyses and modelling of the event by the wider scientific community. Among the most remarkable aspects related to this event are (1) the relation between the recent event and somewhat smaller but quite similar events that occurred earlier in historical times (1835, 1902), (2) the interactions between unstable local geological structures and complex geothermal and hydraulic conditions in the starting zone with permafrost, cold to polythermal hanging glaciers and volcanic effects (hot springs) in close contact with each other, (3) the erosion and incorporation of a debris-covered valley glacier largely enhancing the sliding volume of rocks, ice, firn, snow, water and probably air to a total of about 100 × 10 m³, and (4) the astonishingly high flow velocities (up to 300 km h ¹) and enormous length of travel path (18 km plus 15 km of debris/mud-flow). This extraordinary case illustrates that large catastrophic events in high mountain regions typically involve a multitude of factors and require integrated consideration of complex chains of processes, a task which must be undertaken by qualified groups of experts.

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A mathematical model of snow-cover influence on soil freezing, taking into account the phase transition layer, water migration in soil, frost heave and ice-layer formation, has been developed. The modeled results are in good agreement with data observed in natural conditions. The influence of a possible delay between the time of negative temperature establishment in the air and the beginning of snow accumulation, and possible variations of the thermophysical properties of snow cover in the wide range previously reported were investigated by numerical experiments. It was found that the delay could change the frozen-soil depth up to 2–3 times, while different thermophysical characteristics of snow changed the resulting freezing depth 4–5 times.

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Comparison of two methods of measurements of snow cover thickness on the glacier Austre Grønfjordbreen, Svalbard was performed in the spring of 2014. These methods were the radar (500 MHz) observations and standard snow surveys. Measurements were conducted in 77 different points on the surface of the glacier. A good correlation (R 2 = 0.98) was revealed. In comparison with the data of snow surveys, the radar measurements show a similar but more detailed pattern of the distribution of the snow cover depth. The discrepancy between the depths of snow cover on maps plotted from data of both methods did not exceed 30 cm in most parts of the glacier. The standard error of interpolation of the radar data onto the entire glacier surface amounts, on average, to 18 cm. This corresponds to the error of radar measurements of 18.8% when an average snow depth is about 160 cm and 9.4% at its maximum thickness of 320 cm. The distance between the measurement points at which the spatial covariance of the snow depth disappears falls between 236 and 283 m along the glacier, and between 117 and 165 m across its position. We compared the results of radar measurements of the pulse-delay time of reflections from the base of the snow cover with the data of manual probe measurements at 10 points and direct measurements of snow depth and average density in 12 snow pits. The average speed of radio waves propagation in the snow was determined as V cr = 23.4±0.2 cm ns −1 . This magnitude and the Looyenga and Kovacs formulas allowed estimating the average density of snow cover ρ L = 353.1±13.1 kg m −3 and ρ K = 337.4±12.9 kg m −3 . The difference from average density measured in 12 pits ρ av.meas = 387.4±12.9 kg m −3 amounts to −10.8% and −14.8%. In 2014, according to snow and radar measurements, altitudinal gradient of snow accumulation on the glacier Austre Grønfjordbreen was equal to 0.21 m/100 m, which is smaller than the average values (0.35 m/100 m). According to the results of snow measurements of 2011-2014, the average thickness of the snow cover on the glacier Austre Grønfjordbreen was by 17 cm greater than in 1979. In the very snowy year 2012, it was higher by 21.5 cm in comparison with the year 1979, and its spatial variability (standard deviation σН) had increased by 25.6 cm. Estimates of spatial and temporal variability of snow cover depth will be used to analyze the hydrothermal state of the glacier and its changes with regard to revealed features and climatic trends.