ИСТИНА

Superficial moraine on the Djankuat Glacier, the best explored in Russia, thickened greatly over the last 3 decades. Total volume of lithogenic matter experienced 141% increment, judging by 3 complete debris thickness surveys since 1983. Ongoing deglaciation provokes intensive rockfalls and subsequent colluvium delivery onto the glacier snout. Covering 2% of the entire glacier area in 1968, debris share grew up to 13% by 2010 (6.5-fold enlargement during 42 years). It influenced mass balance values and distorted its spatial pattern. Debris renders a general screening effect upon melt-rate, and glacier-derived liquid bulk run-off turns out to be reduced annually by ca. 20% on average. Glacier topography and mass balance patterns by 2025 were predicted based on HadCM3 climate model (A2 scenario). Downscaling air temperature and precipitation and considering anticipated debris cover evolution showed that debris-covered parts would experience lowering 7-15 m less than clean ice, and lowering rate would be 42-45% smaller. Hence, debris cover evolution seems currently to have significance for glacier behaviour comparative with climate change factor. 3D simulation of the glacier was also undertaken for 150 years henceforth in compliance with conditions of unchanging climate for 2 alternative modelling options - with vs. without screening effect of debris. Disregard of this protective mechanism overestimates volume reduction by 9% and frontal retreat by 500 m; in this option splitting of the glacier body into separate parts takes place sooner, and its area becomes smaller by 12% against only 3% in case of taking debris cover evolution into account.