Ice-contact lakes and their influence on Himalayan glacier evolution

Mountain glaciers are rapidly losing mass due to climate warming. In the Himalaya, this threatens downstream communities that rely on the meltwater for hydropower, irrigation and sanitation. However, projections of future glacier change are hindered by limited empirical data and the omission of key processes, particularly interactions with ice-contact lakes, which can enhance melt and flow but are often oversimplified or excluded from numerical models. This thesis addresses this gap through a multi-temporal, multi-disciplinary investigation of the role of ice-contact lakes in past, present and future Himalayan glacier evolution. Remotely sensed datasets of glacier velocity, surface elevation change, and lake area were combined to quantify the evolution of >350 lake- and land-terminating glaciers across the Himalaya between 2000 and 2019. Glacier response varied according to the lake evolutionary stage. In the Eastern Himalaya, where lakes are larger and more numerous, lake-terminating glaciers showed significantly enhanced surface lowering (by 0.14 m a-1), and ice velocity anomaly (by 0.29 m a-1 decade-1) compared with land-terminating glaciers, differences not observed further west. In situ observations provided the first seasonal assessment of thermal dynamics at a Himalayan ice-contact lake (Thulagi Lake, Nepal), revealing a brief but thermally intense stratification period during early monsoon (May to July), with surface temperatures exceeding 9°C. However, in comparison to observations from other glacierised regions, the summer stratification period was shortened from ~5 to ~2 months by glacial meltwater inputs and the monsoon. Numerical modelling of Thulagi Glacier assessed the combined influence of supraglacial debris, which prolonged glacier extent by up to 122 years, and ice-contact lakes, which accelerate short-term mass loss by up to 35%. Although ice-contact lakes may not significantly alter total glacier mass loss projections over centennial timescales, neglecting their short-term effects generates substantial uncertainties in the timing of mass loss.