Glacier No. 4 of Sigong River over Mt. Bogda of eastern Tianshan, central Asia: thinning and retreat during the period 1962-2009

RTK-GPS data, aerial photographs and Aster images were used to quantify volume, surface elevation, terminus position and area changes of Glacier No. 4 of Sigong River over Mt. Bogda, Tianshan during the period from 1962 to 2009. Glacier surface elevation of the tongue area decreased by 15 +/- A 8 m (0.32 +/- A 0.17 m a(-1)) and ice volume loss reached 0.014 +/- A 0.008 km(3) (0.013 +/- A 0.007 km(3) w. e.). The glacier terminus retreated at a rate of 8.0 m a(-1) and the area decreased by about 0.53 km(2), accounting for 15.8% of the glacier area in 1962 (3.33 km(2)). The changes can be primarily attributed to the significant increase in temperature in this region. A comparison with glacier changes by field measurements in other regions of eastern Tianshan showed obvious spatial differences in the magnitude of the changes, owing to a combination of regional climate change and topographical factors.