Supra-glacial debris cover changes in the Greater Caucasus from 1986 to 2014

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.