Contrasting thinning patterns between lake- and land-terminating glaciers in the Bhutanese Himalaya

• Published in: The Cryosphere
• Main Authors: S. Tsutaki, K. Fujita, T. Nuimura, A. Sakai, S. Sugiyama, J. Komori, P. Tshering
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2019
• Subjects: geo; envir; Glacial Lake; The Cryosphere
• Online Access: https://doi.org/10.5194/tc-13-2733-2019; https://www.the-cryosphere.net/13/2733/2019/tc-13-2733-2019.pdf; https://doaj.org/article/6f113b681e084c579a349ea1027a3743

Despite the importance of glacial lake development in ice dynamics and glacier thinning, in situ and satellite-based measurements from lake-terminating glaciers are sparse in the Bhutanese Himalaya, where a number of proglacial lakes exist. We acquired in situ and satellite-based observations across lake- and land-terminating debris-covered glaciers in the Lunana region, Bhutanese Himalaya. A repeated differential global positioning system survey reveals that thickness change of the debris-covered ablation area of the lake-terminating Lugge Glacier (-4.67±0.07 m a−1) is more than 3 times more negative than that of the land-terminating Thorthormi Glacier (-1.40±0.07 m a−1) for the 2004–2011 period. The surface flow velocities decrease down-glacier along Thorthormi Glacier, whereas they increase from the upper part of the ablation area to the terminus of Lugge Glacier. Numerical experiments using a two-dimensional ice flow model demonstrate that the rapid thinning of Lugge Glacier is driven by both a negative surface mass balance and dynamically induced ice thinning. However, the thinning of Thorthormi Glacier is minimised by a longitudinally compressive flow regime. Multiple supraglacial ponds on Thorthormi Glacier have been expanding since 2000 and have merged into a single proglacial lake, with the glacier terminus detaching from its terminal moraine in 2011. Numerical experiments suggest that the thinning of Thorthormi Glacier will accelerate with continued proglacial lake development.