Proglacial Lakes Elevate Glacier Surface Velocities in the Himalayan Region

Abstract

Himalayan glaciers melt into the Ganges and Brahmaputra river catchments that provide water to over half a billion people. Upstream areas are likely to be affected substantially by climate change, and changes in meltwater supply will locally have tremendous consequences for downstream populations. About 10% of the Himalayan glacier population terminates into pro-glacial lakes and such lake-terminating glaciers are known to be capable of accelerating total mass losses by a well studied phenomena called dynamic thinning. However, evidence for dynamic thinning on Himalayan lake-terminating glaciers is sparse and studies available are only local in nature. Here we present, by employing the Sentinel-2 optical satellites, a 2017-2019 glacier surface velocity dataset covering most of the Central and Eastern Himalayan glaciers larger than 3km2. We find that centre flow line velocities of lake-terminating glaciers are more than twice as high as land terminating glaciers (18.8 to 8.24 m/year), and show substantially more heterogeneity at the glacier snout. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning and show that about half of the lake-terminating glacier, of which most clean-ice, show an acceleration towards the terminus. Many of these clean-ice lake terminating glaciers are disproportionately large and drain into the highly melt-water dependent Brahmaputra basins. With continued warming new lake development is likely to happen and will further accelerate future ice mass losses; a scenario not currently considered in regional projections.