GLACIAL GEOMORPHOLOGY OF THE PURUOGANGRI, THE LARGEST ICE FIELD, IN THE TIBETAN PLATEAU

The Puruogangri ice field is located in the center of the Tibetan Plateau. It is composed of several ice caps with a total glacier area of more than 400 km². The landscape is gentle with an average slope of several degree with average annual temperature below zero celsius. The glacial valley is shallow and short. The peaks shaped by glacial erosion do not display pyramid shape which is common in mountain glaciers, but display subrounded. Few roche moutonnees were found the northern side. The moraines are short with several meters to thirty meters high. These geomorphological characteristics indicate that glacial erosion and sedimentation are weak in this cold and dry area. However, striations and polished surface on boulders are common, suggesting strong subglacial sliding due to geothermal heating beneath ice. The largest paleoglaciers extended more than ten kilometers and crossed the piedmont to the opposite side of the mountains on the eastern, northwestern and southern sides, and crossed the piedmont thirty kilometers to the shore of the Linggecuo Lake on the western side, leaving huge moraines. The other moraines are within the valleys or distribute in the piedmont within several tens of meters to several kilometers to modern glacier snouts. Moraines are preserved very well due to little erosion in gentle landscape, cold environment and low precipitation. More than ten of moraines sequences are identified for future dating.