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).
Анализируются результаты радиолокационных измерений и моделирования толщины льда опорного для Центрального Кавказа ледника Джанкуат. Несмотря на всестороннюю изученность, площадная инструментальная съёмка толщины льда на этом леднике до сих пор не проводилась. В 2012-2013 гг. на леднике Джанкуат при помощи моноимпульсного радиолокатора ВИРЛ-6 с центральной частотой 20 МГц пройдено более 20 км профилей, перекрывающих основную часть ледника. Стандартная ошибка измерений составила 2,5% измеряемой величины. Впервые были построены детальные карты толщины льда и подлёдного рельефа ледника, основанные на фактических данных. Максимальная измеренная толщина ледника составляет 105 м при средней толщине 31 м. Объём ледника Джанкуат без учёта Джантуганского плато, согласно данным инструментальных измерений, составил 0,077±0,002 км 3. Карты толщины льда, построенные на основе радиолокационных измерений, дополнены результатами моделирования толщины льда с помощью модели GlabTop. Показано, что модель достоверно воспроизводит распределение толщины льда. Предложен и реализован подход, позволяющий корректировать параметры модели по данным прямых измерений. Results of measurements and modeling of the Djankuat Glacier ice-thickness (Central Caucasus) are presented and discussed. In 2012-2013, more than 20 km of radio-echo sounding profiles covering the main area of the glacier were obtained using monopulse radar VIRL-6 with its central frequency of 20 MHz. The first detailed maps of the ice-thickness and the bedrock topography were constructed these data. According to the measurements the maximum and average values of the ice thickness are 105 m and 31 m, respectively.
Thickness of the upper cold ice layer in the ablation area of the polythermal glacier Grønfjordbreen (Spitsbergen) was estimated by means of numerical modeling. The results were compared with data of radio-echo sounding of the same glacier obtained in 1979 and 2012. Numerical experiments with changing water content in the lower layer of temperate ice and surface snow cover thickness made possible to compare calculated and modeled cold ice thicknesses and to estimate their changes for 33‑year period caused by regional climate change. According to data of radio-echo sounding, thickness of the cold ice layer decreased, on average, by 34 m. Numerical modeling shown similar results: the cold ice layer became thinner by 31 m and 39 m at altitudes 100–300 a.s.l. under the snow cover thickness of 1 m and 2 m. We explain this by rising of annual mean air temperature by 0,6 °С as compared to data of the nearest meteorological station Barentsburg in the same period. We believe that changes in cold ice layer thickness in polythermal glaciers can be used for estimation of changes in such regional climatic parameter as mean air temperature at different altitudes of the glacier surface in the ablation area.
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