Esker

Long, winding ridge of stratified sand and gravel associated with former glaciers

An esker, eskar, eschar, or os (sometimes called an asar, osar, or serpent kame) is a long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America. They are most often formed by the deposition of sediment at the bottom of ice-walled channels within or beneath a former glacier. As a glacier retreats, the channel walls melt while the accumulated sediment remains, slumping into ridges as the only remaining evidence of the former channel path.

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