Subglacial meltwater channel
A steep, often vertically sided valley cut into bedrock by a subglacial stream under high pressure. It may have a profile with uphill sections, since a sufficient head in the glacier can force water to flow up slope.
Subglacial meltwater channel in the proglacial area of Oberaletschgletscher, Bernese Alps, Switzerland. Photo J. Alean, 2005.