SUPERFICIAL MORAINE EXPANSION ON THE DJANKUAT GLACIER SNOUT OVER THE DIRECT GLACIOLOGICAL MONITORING PERIOD

Abstract

A superficial moraine is an inherent attribute of the lower belts of active alpine glaciers at the currently prevalent regressive stage of their evolution. Debris on the glacier snout surface drastically influence ablation and the mass balance of a glacier and thereby the glacier runoff, as well. A superficial moraine at the Djankuat glacier, representative for the Central Caucasus, has been both examined in the course of direct fieldwork and mapped by means of remote sensing. Debris thickness was mapped thrice during the direct monitoring period as a result of three direct surveys, covering the entire debris-covered area of the snout. The study reveals evident debris expansion on the Djankuat snout: accounting for only 2 % of the entire glacier area in 1968, its share grew up to 13 % by 2010, resulting thereby in 6.5-fold enlargement during 42 years. The debris layer became thicker by 70 cm in some points near the terminus during 1983–2010, whereas the volume of the lithogenic matter over the whole glacier experienced 141 % increment. This process has changed the mass balance values and has affected its spatial pattern. In general, the debris cover renders a screening effect upon the melt-rate, and thereby the glacier-derived runoff turns out to be reduced annually by ca. 20 % on average. Glacier, superficial moraine, debris thickness survey, monitoring, mass balance, ablation, Central Caucasus A superficial moraine producing debris for lower parts of glaciers is currently their inherent component. The modern stage of the evolution of alpine glaciers is far and wide characterized by active background deglaciation, which is accompanied by intense accumulation of moraine material on the glacier surface and in the glacier belt. It is most commonly investigated in view of the mudslide hazard coming from the periglacial zone [Tomashevskaya et al., 2013]. However, deglaciation results in the growth of the surface moraine debris on the glacier itself both in terms of the area and thickness. Moraine debris primarily affects all the processes occurring within the limits of the glacier parts covered by it. It predetermines intensity of ablation in these parts and runoff from them and determines the pattern of the mass balance fields and of its discharge component on the snout: a thin (the first centimeters) moraine enhances sub-debris thawing, while a thicker moraine, on the contrary, diminishes it to the extent of complete dis