iwata_2005.htm
Bulletin of Glaciological Research 22 (2005)
99-107
©Japanese Society of Snow and Ice
Debris-mantle formation of Wrputu Glacier,
the Tianshan Mountains, China
Shuji IWATA1, Shinjiro KURODA1, and KADER Kezer2
1 Department of Geography, Tokyo Metropolitan
University, Tokyo 192-0397 Japan
2 Xingchang Institute of Ecology and Geography,
Chinese Academy of Science, Urumqi, China
Abstract
A small valley glacier, Wrputu Glacier, in the Urumqi River basin, the Tianshan Mountains, has a tongue-shaped debris hill in front of a debris-free glacier snout. Two topographical maps, surveyed in 1983 and 2003, indicate that the debris hill surface lowered 5-10 m in elevation for the 20-year interval, and this subsidence occurred on the entire debris hill. The cause of the subsidence is ablation of the underneath glacier ice so that the entire debris hill contains ice. This means that the debris hill is a debris-mantled glacier-snout rather than an ice-cored moraine. The debris mantle has originated from the debris-rich basal-ice layer of the formerly advanced and overrode preexistent glacier. Its scenario is as follows: The preexistent advanced glacier-snout turned to a stagnant snout by the negative mass-balance of the glacier. In the following positive state, glacier thickened and increased its movement rates. The active snout with debris-rich basal-ice layer overrode on the debris-free stagnant-snout and continued to advance. The preexistent debris-free glacial snout turned to the debris-mantled glacier after the overridden glacier stopped its advance and retreated as leaving the residual debris-mantle on the underneath stagnant glacial snout.
