PAST AND PRESENT GLACIER EXTENT IN THE TANGGULA SHAN OF THE QINGHAI-TIBETAN PLATEAU, CHINA

The Tanggula Shan, situated astride the border between the provinces of Qinghai and Tibet in western China, provide an excellent location in which to study the interaction of continental and monsoonal air masses, and their effects on past and present glacier extent. The area around Tanggula Pass contains numerous end moraines that can be grouped into four phases of glaciation on the basis of topographic and surface weathering characteristics. The oldest of these, either the Tanggula or Jazhazangbu phase, is represented by extensive areas of hummocky topography, extending to elevations below 5050 m asl, and 16 to 25 km from modern glacier margins. These moraines define the margins of sizeable piedmont glaciers that drained a large ice cap that covered most of the Tanggula Shan. The Basicuo phase is represented by moraines located 5 to 9 km from the modern glacier margins between elevations of 5050 and 5150 m asl. The surfaces of these moraines are highly weathered, and the only extant boulders are composed of highly resistant sedimentary and igneous lithologies. During the Basicuo phase the Tanggula Shan were partially inundated by several discrete ice fields. The Longxiazai phase is represented by small, poorly preserved moraines located less than 5 km from modern ice margins at elevations above 5150 m asl. Ice at this time was restricted to valleys and minor ice fields. Finally, end moraines located less than 1 km from the margins of modern glaciers likely record the extent of a small Neoglacial advance.

Modern glaciers cover ~300 km^2 in the mapping area. An analysis of the modern equilibrium line altitude (ELA) using a toe-headwall altitude ratio (THAR) of 0.4 indicates an ELA between 5450 and 5600 m asl. Estimates of the paleo-ELA during the oldest glacial phase suggest an ELA lowering of only ~100 m, reflecting the control of the uniform plateau surface (~5000 m asl) on the elevation of glacier termini. Mean summer temperatures at the modern ELA are ~2° C and mean summer water accumulation is ~350 mm. These conditions are more arid than those found at the equilibrium lines of other modern glaciers, indicating that the mass balance of the Tanggula Shan glaciers is negative. Comparison of glacier margins in satellite images from 1964, 1976, 1989, and 2001 confirms that glaciers have retreated >100 meters over the last 40 years.