摘要：Two debris-covered glaciers and two debris-free glaciers were surveyed regarding their surface lowering in the Lunana region, in the northern part of Bhutan. Regarding the debris-covered ones, the lowering rates were estimated to be 0-3 m a-1 and approximately 5 m a-1 on the ablation areas of the Thorthormi and Lugge Glaciers, respectively, in 2002-2004. Glacier flow was also measured for the two glaciers. The results showed contrastively that compressive flow is clear on the Thorthormi Glacier but not on the Lugge Glacier. The contrast in the surface lowering and flow is discussed herein to infer a positive feedback mechanism between glacier shrinkage and glacial lake growth. On the other hand, the surface lowering rates evaluated on debris-free glaciers were 3-4 m a-1 on the lower part of the Jichu Dramo Glacier in 2003-2010, and 1-3 m a-1 on a small unnamed glacier southeast of the Jaze La (pass) in 1999-2010. The lowering rate on the Jichu Dramo Glacier may have accelerated from the previous estimate in 1998-2003. In addition, several pairs of repeated photos are provided to show glacier shrinkages and retreats.
