Esker

An esker is a long, winding ridge composed mainly of sand and gravel that forms from sediment deposited by meltwater streams flowing within or beneath a glacier. Eskers are one of several glacial landforms created in the process of retreat and melting of ice, and they occur in regions formerly covered by large ice sheets during the Quaternary.

Formation and morphology: Subglacial or englacial conduits channel efficiently moving water beneath the ice; as water flows through tunnel channels, sediment carried in suspension and along the bed is deposited. When ice retreats, the sediment remains as a raised ridge above the surrounding terrain. Eskers typically have a sinuous, narrow form, and can extend tens to hundreds of kilometers, with heights ranging from a few to several tens of meters. The sediments are usually well sorted and stratified, reflecting changing flow conditions.

Distribution and significance: Eskers are found in many formerly glaciated regions of the northern hemisphere and in some southern regions, including parts of Canada, the United States, northern and central Europe, Patagonia, and New Zealand. They are valuable as records of subglacial hydrology and ice-margin dynamics and commonly serve as important aquifers because the sorted sands and gravels transmit groundwater easily. They may also host human settlements and provide aggregate for construction in some regions.

Relation to other landforms: Eskers are distinct from moraines, which are accumulations of till deposited at the glacier's edge, and from drumlins, which are streamlined hills of till. They also differ from kames, small mounds formed by sediments in ice-contact settings.