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 supraglacial 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 supraglacial 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 3130ma.s.l. (metres above sea level) during the investigated period.