Elevation changes of Inylchek Glacier during 1974–2007, Central Tian Shan, Kyrgyzstan derived from remote sensing data

Glacier melt is an important source of fresh water for the arid regions surrounding the Tian Shan. Inylchek Glacier (650 km2) is the largest glacier in Tian Shan consisting of two branches (northern Inylchek glacier and southern Inylchek glacier) separated by the regularly draining Lake Merzbacher. However, little is known about volume and mass changes of the last decades. In this study, we investigated the changes of glacier area and glacier surface elevation from 1974 until 2007 and the surface velocity between 2003 and 2011 using multi-temporal remote-sensing data. The main flow direction of Southern Inylchek Glacier tongue showed strong velocities of ∼100 m a−1 with a slight decreasing tendency between 2002/03 and 2010/11. The end of the tongue however, is likely stagnant as the main flow is directed towards Lake Merzbacher. The total glacier area increased by 1.3 ± 0.1 km2 (∼0.2%) within the studies period though southern Inylchek Glacier shrank consecutive since 1974. The overall area gain was caused by the strong increase of northern Inylchek Glacier of 3.7 ± 0.3 km2 between 1990–1999. A comparison of glacier surface elevation using multi-temporal digital elevation models derived from KH9-Hexagon (1974), SRTM (1999), ALOS (2006) and SPOT5-HRG (2007) revealed an overall elevation difference of Inylchek Glacier of −0.5 ± 0.1 m a−1 for the period of 1974–2007. The northern glacier branch showed on average no significant surface elevation change (0.1 ± 0.1 m a−1) during 1974 and 2007 while a significant lowering of 0.7 ± 0.1 m a−1 was observed for the southern branch. The overall negative values are mainly due to the period 1974–1999. A possible thickening of 0.5 ± 0.5 m a−1 occurred between 1999 and 2007 where a clear thickening was measured in the accumulation area of the southern branch. We also identified the thickening with a maximum of about ∼150 m close to the end of the northern Inylchek Glacier tongue for the period 1974–1999. This is possibly due to a surge event which happened between 1990 and 1999 according to the area change data. The ablation region of southern Inylchek Glacier showed considerable lowering rates especially in the distal part of the tongue with low velocity despite thick debris coverage.