eskers

Eskers are long, winding ridges of coarse sediment that form from meltwater streams within or beneath glaciers during deglaciation. As subglacial rivers carried sand and gravel through tunnels inside or under the ice, the flowing water deposited sorted sediments on the channel floor. When the ice retreated, the deposited ridge remained as a raised, sinuous crest. Eskers commonly extend for kilometers and can reach tens of meters in height; their form records the path and behavior of meltwater beneath the ice.

The ridges are typically composed of stratified, well-sorted sand and gravel, often with cross-bedding or imbrication from migrating channels. Clay and finer sediments are generally scarce, though occasional silty layers occur. Eskers can occur singly or as part of a network, reflecting multiple subglacial channels. Because they formed within ice, they contrast with moraines, which are accumulations of debris pushed at the glacier’s edge, and with outwash plains, which form from meltwater emerging at the glacier front.

In landscapes formed by former glaciations, eskers provide clues about past ice thickness, drainage directions, and meltwater pathways. They are significant for understanding palaeoglaciology and, in many regions, serve as important aquifers due to their permeable sediments.

The name esker comes from the Irish Gaelic eiscir, meaning ridge. Eskers are found in many formerly glaciated regions of North America and Europe, including Canada, the United States, Scandinavia, and Britain.