Understanding supraglacial drainage networks on mountain glaciers using high‑resolution orthophotos, UAV imagery and field data

Supraglacial channels play a fundamental role in efficiently transporting surface meltwater across, into, and beyond glacier systems, with implications for surface mass balance, glacier dynamics, and the hydrochemistry of glacier runoff. Although such channels have been frequently documented in ice sheet settings, the resolution of satellite imagery makes similar studies on mountain glaciers challenging, and field observations remain scarce. Here, we combine uncrewed aerial vehicle (UAV) imagery, field measurements, and historical aerial photographs to conduct high-resolution mapping of supraglacial channels on Glacier du Brenay in the Swiss Alps, which provides new insights into their distribution and characteristics. Our results reveal a dense pattern of broadly dendritic channel networks influenced by ice surface structures. We find that most first-order channels, which are only visible in UAV imagery, terminate englacially in crevasses. Consequently, englacial routing is likely more widespread at Glacier du Brenay than suggested by coarser resolution imagery, where the larger and more detectable channels often flow off the glacier terminus. Channel size and distribution are influenced by the glacier’s surface profile, which dictates the location and extent of channel catchments. Larger upstream-originating catchments are associated with increased channel dimensions, and where deeply incised channels from these catchments flow off the terminus, they are associated with rapid retreat at the proglacial margin. We find that continuous debris cover produces shallow channels and results in increased channel roughness, decreased water velocity, and reduced surface lowering rates. In contrast, discontinuous debris is associated with the highest rates of surface lowering and can produce pitted topography, which also increases channel roughness. Future research should therefore consider small-scale hydrological processes.