An esker is a long, winding ridge of stratified sand and gravel deposited by meltwater streams flowing beneath a glacier. Eskers are significant features in glacial geomorphology, providing evidence of past glacial dynamics and meltwater processes. They are also important in hydrogeology as potential aquifers.
Source Shreve, R. L. (1985). “Eskers, Kames, and Subglacial Drainage Channels.” Geological Society of America Bulletin, 96(5), 639-646.