Abstract
Abstract. Knowledge of supra-glacial debris cover and its changes remain incomplete in the Greater Caucasus, in spite of recent glacier studies. Here we present data of supra-glacial debris cover for 659 glaciers across the Greater Caucasus based on Landsat and SPOT images from the years 1986, 2000 and 2014. We combined semi-automated methods for mapping the clean ice with manual digitization of debris-covered glacier parts and calculated supra-glacial debris-covered area as the residual between these two maps. The accuracy of the results was assessed by using high-resolution Google Earth imagery and GPS data for selected glaciers. From 1986 to 2014, the total glacier area decreased from 691.5±29.0 to 590.0±25.8 km2 (15.8±4.1 %, or ∼0.52 % yr−1), while the clean-ice area reduced from 643.2±25.9 to 511.0±20.9 km2 (20.1±4.0 %, or ∼0.73 % yr−1). In contrast supra-glacial debris cover increased from 7.0±6.4 %, or 48.3±3.1 km2, in 1986 to 13.4±6.2 % (∼0.22 % yr−1), or 79.0±4.9 km2, in 2014. Debris-free glaciers exhibited higher area and length reductions than debris-covered glaciers. The distribution of the supra-glacial debris cover differs between the northern and southern and between the western, central and eastern Greater Caucasus. The observed increase in supra-glacial debris cover is significantly stronger on the northern slopes. Overall, we have observed up-glacier average migration of supra-glacial debris cover from about 3015 to 3130 m a.s.l. (metres above sea level) during the investigated period.
Highlights
Supra-glacial debris cover affects surface melt with increasing ablation in cases of thin debris cover or decreasing ablation under continuous thick debris cover (Östrem, 1959; Nicholson et al, 2018)
We found an absolute increase in supra-glacial debris cover for all investigated glaciers, from 48.3 ± 3.1 km2 in 1986 to 54.6±3.4 km2 in 2000 and 79.0±4.9 km2 in 2014, in contrast to a reduction of the total glacier area
For all regions investigated in the Greater Caucasus the rate of increase in supra-glacial debris cover varied between northern and southern slopes and between the western, central and eastern sections of the mountain range (Table 2; Figs. 3, 4)
Summary
Supra-glacial debris cover affects surface melt with increasing ablation in cases of thin debris cover (less than a few cm) or decreasing ablation under continuous thick debris cover (Östrem, 1959; Nicholson et al, 2018). Obtaining information about debris cover is relevant with respect to its impact on glacier ablation and because it is an important part of the sediment transport system Tielidze et al.: Supra-glacial debris cover changes in the Greater Caucasus glacial, englacial and subglacial) in cold and high mountains (Kellerer-Pirklbauer, 2008), which affect the overall dynamics and mass balance of the glaciers. Several studies show an increase in debris-covered area with overall glacier shrinkage and mass loss (Deline, 2005; Stokes et al, 2007; Kirkbride and Deline; 2013; Glasser et al, 2016)
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