Assessing the distribution and characteristics of supraglacial channels in an Alpine setting

Supraglacial channels are an increasingly common glaciological feature due to intensifying surface melt and form a key component of glacier hydrology and mass balance, transporting meltwater to englacial, subglacial, and peripheral positions. Whilst their occurrence is becoming increasingly well-documented on ice sheets, little is known about the distribution of channels on mountain glaciers, which often fall below the resolution of commercial satellites. Using high-resolution orthophoto imagery (~10 cm) and digital elevation models (~0.5 m), we provide the first inventory of supraglacial channels in an alpine environment, focusing on Valais Canton, Switzerland. We manually delineated 1890 channel segments on 85 glaciers, recording glacier characteristics across all 207 snow-free glaciers >0.1 km² in Valais Canton, encompassing glaciers of differing debris-cover, altitude, and slope. We find that channel segments have a mean length of 212 m and a slope of 8°, with most channels exhibiting low sinuosity (mean: 1.1) and those with higher sinuosity (max: 3.8) only existing on very low surface slopes (<5°). Glaciers containing supraglacial streams have a mean area of 5.0 km², with a mean drainage density of 1.0 km/km² (max: 11.0 km/km²) and are likely to extend to lower elevations (mean: 2797 m.a.s.l). Conversely, glaciers without streams are smaller, with a mean area of 0.6 km², and have a higher minimum elevation (mean: 2945 m.a.s.l). Our observations suggest that the highest drainage densities are found on glaciers characterised by low surface slopes, large ablation areas, low crevasse densities, and limited debris cover. Additionally, stream sinuosity and length appear to be controlled by glacier structure (i.e., crevasses and moulins), slope, and debris content. Our future work will expand on these results using field-based investigations to directly measure channel characteristics and improve estimates of the proportion of meltwater transported as supraglacial run-off versus that entering en- and sub-glacial pathways.