ALBERT

Description: 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.

Description: Glacier melt is an essential source of freshwater for the arid regions surrounding the Tian Shan. However, the knowledge about glacier volume and mass changes over the last decades is limited. In the present study, glacier area, glacier dynamics and mass changes are investigated for the period ~1975–2007 for Southern Inylchek Glacier (SIG) and Northern Inylchek Glacier (NIG), the largest glacier system in Central Tian Shan separated by the regularly draining Lake Merzbacher. The area of NIG increased by 2.0 ± 0.1 km2 (~1.3%) in the period ~1975–2007. In contrast, SIG has shrunk continuously in all investigated periods since ~1975. Velocities of SIG in the central part of the ablation region reached ~100–120 m a−1 in 2002/2003, which was slightly higher than the average velocity in 2010/2011. The central part of SIG flows mainly towards Lake Merzbacher rather than towards its terminus. The measured velocities at the distal part of the terminus downstream of Lake Merzbacher were below the uncertainty, indicating very low flow with even stagnant parts. Geodetic glacier mass balances have been calculated using multi-temporal digital elevation models from KH-9 Hexagon (representing the year 1975), SRTM3 (1999), ALOS PRISM (2006) and SPOT-5 high-resolution geometrical (HRG) data (2007). In general, a continuous mass loss for both SIG and NIG could be observed between ~1975 and 2007. SIG lost mass at a rate of 0.43 ± 0.10 m w.e. a−1 and NIG at a rate of 0.25 ± 0.10 m w.e. a−1 within the period ~1975–1999. For the period 1999–2007, the highest mass loss of 0.57 ± 0.46 m w.e. a−1 was found for NIG, whilst SIG showed a potential moderate mass loss of 0.28 ± 0.46 m w.e. a−1. Both glaciers showed a small retreat during this period. Between ~1975 and 1999, we identified a thickening at the front of NIG with a maximum surface elevation increase of about 150 m as a consequence of a surge event. In contrast significant thinning (〉0.5 m a−1) and comparatively high velocities close to the dam of Lake Merzbacher were observed for SIG, indicating that Lake Merzbacher enhances glacier mass loss.