Glacial meltwater is produced by the melting of glacier ice at the surface, or by pressure and geothermal heat at the base, forming subglacial streams. Some surface meltwater may percolate through the ice to emerge at the base. Both subglacial and proglacial meltwater erosion are extremely effective agents of landscape change. Water often flows under pressure within and below decaying ice, pressure that enables meltwater to flow upslope, and carry large quantities of debris, which promotes abrasion.

Glacial meltwater landforms

form subglacially; at or near the ice margin; and in proglacial settings. Ice margin meltwater follows the edge of the glacier when drainage routes have been cut off by ice. Tunnel valleys occur below the ice and can cut steep-sided, flat-floored valleys; see Cutler et al. (2002) Quat. Int. 90, 1. Spillways are channels cut by streams overflowing from proglacial lakes; see Thieler et al. (2007) Pal. Pal. & Pal. 246, 1. Coulees are canyons which result from the sudden and violent release of water from ice-dammed lakes when the barriers which impound them are breached. See Shaw (2002) Quat. Int. 90, 1 on the meltwater hypothesis for subglacial bedforms, and Hannah and Gurnell (2001) J. Hydrol. 246, 1 and Pohl et al. (2005) Atmos-Ocean 43, 3 for models of meltwater action. For meltwater and the reconstruction of former ice sheets, see Clark and Mix (2002) Quat. Sci. Revs 21, 1–3. See also Glasser et al. (2004) Boreas 33, 3 on meltwater processes as evidence for multiple glaciations.