Khumbu Glacier (27.962 °N, 86.826 °E) is a 12.0 km long, 45.6 km2 debris-covered glacier flowing southward from Mt. Everest, with an ablation area of ~20 km2 below the foot of a major icefall. Its climatic and geologic setting combined with its surface and dynamic characteristics make the Khumbu Glacier highly representative of all large, Himalayan debris-covered glaciers, ensuring the data we collect will have broad application across the range. The glacier is heavily in recession; ice flow reaches a maximum velocity of approximately 70 m a-1, and is lowest in the final 4 km of the debris-covered tongue which may be at least partially stagnant11. Field measurements made by Gades et al. (2000) using electrical resistivity indicated ice thickness was 440 ± 20 m at 0.5 km below the icefall, decreasing to less than 20 m at 4930 m, 2 km upstream of the terminus44 (Figs. 1 and 2).
Surface debris thickness increases from the base of the icefall to the glacier terminus, but sluicing of debris down steep slopes frequently reveals clean ice surfaces and a growing number of surface ponds exist where clean ice can be accessed for drilling. While thick layers of englacial debris have been observed at neighbouring Lhotse Glacier and have been hypothesised to exist at Khumbu Glacier25, our own observations at numerous surface exposures, as well as published images from speleological investigations36,37, suggest that the debris entrained within Khumbu is generally of fine texture and exists in less concentrated layers.