Retreat and geodetic mass changes of Zemu Glacier, Sikkim Himalaya, India, between 1931 and 2018

This study assessed changes in the snout, area, and mass of the largest glacier, Zemu, located in Sikkim Himalaya using earth observation data of 87 years from 1931 to 2018. GlabTop model was used to estimate the glacier thickness and potential lakes that could develop in the future. The study assumes importance since massive hydropower infrastructure is being set up without incorporating any knowledge about the retreating glaciers in the region. Between 1931 and 2018, the glacier lost 30.67% (+/- 2.87%) at a rate of 0.35% per year. The snout of the glacier retreated by similar to 797 m (+/- 19.7 m) between 1931 and 2018 at a rate of 9.1 m a(-1). The rate of retreat increased to similar to 20 m a(-1) very recently from 2014 to 2018. The geodetic mass balance estimates suggest that the glacier lost 6.78 Gt (+/- 2.05 Gt) of mass at a rate of 84.8 Mt a(-1) between 1931 and 2012. The mass loss accelerated at 276.5 Mt a(-1) between 2000 and 2012. The GlabTop results suggest a mean glacier thickness of 117 m and the formation of a potential future proglacial lake with an area, volume, and peak discharge capacity of 25.3 ha, 3.53 million m(3), and 3522 m(3)s(-1), respectively, by the end of this century.