Abstract
Abstract. The glacier coverage in the Caucasus Mountains underwent considerable changes during the last decades. In some regions, the observed reduction in glacier area is comparable to those in the European Alps and the extent of supra-glacial debris increased on many glaciers. Only a few glaciers in the Caucasus are monitored on a regular basis, while for most areas no continuous field measurements are available. In this study, regional differences of the conditions for glacier melt with a special focus on debris covered glacier tongues in the well-studied Adyl-su basin on the northern slope of the Caucasus Mountains (Russia) is compared with the Zopkhito basin which has similar characteristics but is located on the southern slope in Georgia. The paper focuses on the effect of supra-glacial debris cover on glacier summer melt. There are systematic differences in the distribution and increase of the debris cover on the glaciers of the two basins. In the Adyl-su basin an extensive debris cover on the glacier tongues is common, however, only those glacier tongues that are positioned at the lowest elevations in the Zopkhito basin show a considerable extent of supra-glacial debris. The observed increase in debris cover is considerably stronger in the north. Field experiments show that thermal resistance of the debris cover in both basins is somewhat higher than in other glaciated regions of the world, but there is also a significant difference between the two regions. A simple ablation model accounting for the effect of debris cover on ice melt shows that melt rates are considerably higher in the northern basin despite a wider debris distribution. This difference between the two regions can be attributed to different meteorological conditions which are characterised by more frequent cloud cover and precipitation in the south. Furthermore ablation is strongly influenced by the occurrence of supra-glacial debris cover in both basins, reducing the total amount of melt on the studied glaciers by about 25 %. This effect mitigates glacier retreat in the lower sectors of the ablation zones considerably. The sensitivity to moderate changes in the debris cover, however, is rather small which implies only gradual changes of the melt regime due to debris cover dynamics during the near future.
Highlights
Debris covered glaciers are common in many mountain regions of the world and the observed retreat of glaciers is accompanied by an increasing extent of debris cover on glacier tongues (Scherler et al, 2011)
A simple ablation model accounting for the effect of debris cover on ice melt shows that melt rates are considerably higher in the northern basin despite a wider debris distribution
Debris cover has a moderate effect on the melt water production
Summary
Debris covered glaciers are common in many mountain regions of the world and the observed retreat of glaciers is accompanied by an increasing extent of debris cover on glacier tongues (Scherler et al, 2011). In addition to process studies, large scale mapping of debris cover is important for a realistic estimation of melt water production by debris covered glaciers (Taschner and Ranzi, 2002; Mihalcea et al, 2008a; Hagg et al, 2008). This is best achieved by the use of satellite imagery (Paul et al, 2004; Stokes et al, 2007) and an important aim of a number of studies was the determination of supra-glacial debris thickness using remote sensing information (Mihalcea et al, 2008b; Foster, 2010). We attempt to integrate field measurements, the analysis of remote sensing imagery and a simple ablation model for evaluating the role of the debris cover on the ice melt for two small basins in the Caucasus Mountains, located north and south of the main divide, where at least some glaciological and meteorological information is available for longer periods
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