Contrasting geometric and dynamic evolution of lake and land-terminating glaciers in the central Himalaya

The impact of glacial lake development on the evolution of glaciers in the Himalaya is poorly quantified, despite the increasing prevalence of supraglacial and proglacial water bodies throughout the region. In this study we examine changes in the geometry, velocity and surface elevation of nine lake-terminating and nine land-terminating glaciers in the Everest region of the central Himalaya over the time period 2000 to 2015. The land-terminating glaciers we examined all decelerated (mean velocity change of - 0.16 to -5.60 m a(-1) for different glaciers), thinned most in their middle reaches, and developed a more gently sloping surface ( -0.02 to -0.37 degrees change) down-glacier over the period 2000-2015. The lake-terminating glaciers we examined all retreated (0.46 to 1.42 km), became steeper (0.04 to 8.68 degrees change), and showed maximum thinning towards their termini, but differed in terms of their dynamics, with one group of glaciers accelerating (mean speed-up of 0.18 to 8.04 m a(-1)) and the other decelerating (mean slow-down of -0.36 m a(-1) to -8.68 m a(-1)). We suggest that these two scenarios of glacier evolution each represent a different phase of glacial lake expansion; one that is accompanied by increasingly dynamic glacier behaviour and retreat, and a phase where glacial lakes have little impact on glacier behaviour that may precede or follow the phase of active retreat. Our observations are important because they quantify the interaction of glacial lake expansion with glacier ice mass loss, and show that increased glacier recession should be expected where a glacial lake has begun to develop.