Distribution and characteristics of supraglacial channels on mountain glaciers in Valais, Switzerland

Abstract. Supraglacial channels form a key component of glacier hydrology, transporting surface meltwater to englacial and proglacial positions, which impacts ice flow dynamics, surface mass balance and the hydrochemistry of glacial runoff. The presence of supraglacial channels is well-documented on ice sheets using satellite imagery, but little is known about their distribution and characteristics on smaller mountain glaciers because most channels fall below the resolution of freely-available satellite imagery. Here we use high-resolution (0.15 m) orthophotos to delineate <2000 supraglacial channels (> 0.5 m wide) across a sample of 285 glaciers, 85 of which contain channels, in Valais Canton, Switzerland, and investigate their distribution and characteristics. We find that glacier hypsometry, size and slope are good predictors of drainage density, with glaciers characterised by lower relief slopes (with fewer crevasses) and larger ablation areas (high meltwater supply) exhibiting higher drainage densities. Drainage density is higher when glaciers terminate at mid-range elevations (2600 – 3100 m.a.s.l), likely due to less surface lowering than at lower elevations, which allows channels to persist. On average, 80 % of high order channels run-off supraglacially, with 20 % terminating englacially. However, there is marked inter-glacier variability in where channels terminate, with 40 % of glaciers containing no englacially-terminating channels, versus 3.5 % where all channels are terminate englacially. Most channels are slightly sinuous, with higher sinuosities associated with large, high-order channels that are heavily incised and more likely to reactivate annually. In comparison to ice sheets, the majority of channels reach the terminus supraglacially and little meltwater is stored in lakes.