Changes of the mass balance of the Garabashy Glacier, Mount Elbrus, at the turn of 20th and 21st centuries

Long-term series of observations on the glacier of the southern slope of Elbrus manifest the change of two climatic periods in the highlands of the Caucasus. During the first one, relatively cold and snowy period of 1982–1997 with a small positive mass balance, the Garabashi Glacier accumulated a layer of 0.8 m.e. The second period (1998–2017) is characterized by rising summer air temperatures and increasing precipitation in the first decade, and catastrophic melting in 2010–2017. The mass balance of the glacier averaged −0.63 m w.e. yr−1, and in some years it reached −1.00 ÷ −1.50 m w.e. yr−1. In the last ten years, frequency of vast anticyclones covering the southern part of the European part of Russia and the North Caucasus increased. Summer temperatures in the Elbrus region rose to almost the level of the 1950s that was the hottest decade of the XX century. Duration of the summer season on the glaciers increased. Active melting resulted in elevation of the equilibrium line of the Garabashy Glacier by 200 m. In the main part of the glacier alimentation area, i.e. at heights of 3800–4000 m, the large parts of the firn area had disappeared, but open ice of the ablation zone had appeared. The former areas of the "warm" firn zone, where up to 35% of melt water retained within the 20‑meter firn thickness, were replaced by the firn-ice zone, and the ice discharge increased. The glacier alimentation is decreased, and its tongue retreats with increasing velocity. Rocks and entire lava ridges release from ice at different levels of the glacier. The inter-annual variations of the glacier mass balance are controlled by intensity of ablation. In the second period, the correlation coefficient of these values reached 0.97 compared to 0.82 in the first one. In total over 36 years of observations, reduction of the glacier mass during the second period resulted in loss of volume (0.05 km3 or 14%), area (0.51 km2 or 11.4%), and of ice layer (11.4 m).