outwash

Outwash refers to sediment deposited by meltwater flowing from a glacier beyond its terminus. Outwash deposits are part of glaciofluvial geology and consist mainly of well-sorted sands and gravels laid down by flowing meltwater, in contrast to the unsorted, unstratified material deposited directly by ice (till).

Formation and processes: Meltwater streams emerge from the glacier, often forming braided networks as they slow and spread upon entering front-facing plains. The water sorts the sediment, producing layered, cross-bedded gravels and sands. Seasonal and climatic variations create complex stratigraphy, with channel belts, levees, and terraces. In addition to the main plains, glaciofluvial action can form features such as eskers (meltwater channels deposited in tunnels within or beneath the ice), kames (mounds of sorted material deposited in ice margins), and kettles (depressions formed by melting blocks of ice left in outwash).

Geomorphology and properties: Outwash plains are typically flat to gently sloping and often extensive, reflecting the proglacial extent of the former ice sheet. The sediments are relatively porous and permeable, making outwash deposits important aquifers in some regions. The deposits are characteristically well sorted and stratified, with sedimentary structures shaped by flowing water rather than ice contact.

Significance: Outwash plains record patterns of glacial retreat and meltwater discharge, contributing to reconstruction of Quaternary geology. They have economic relevance for gravel resources and groundwater storage and can influence landscape rehabilitation after glacial periods.