Esker

Esker (O. Irish eiscir), a local name for long mounds of glacial gravel frequently met with in Ireland. Eskers (the Swedish åsar) are among the occasionally puzzling relics of the British glacial period. They wind from side to side across glaciated country and have evidently been formed by channels upon or under the ice. “Where streams of considerable size form tunnels under or in the ice these may become more or less filled with wash, and when the ice melts the aggraded channels appear as long ridges of gravel and sand known as eskers. It has been thought that similar ridges are sometimes formed in valleys cut in the ice from top to bottom, and even that they rise from gravel and sand lodged in super-glacial channels. The latter at least is probably rare, as the surface streams have usually high gradients, swift currents and smooth bottoms, and hence give little opportunity for lodgment. In the case of ice-sheets, too, in which eskers are chiefly developed, there is usually no surface material except at the immediate edge, where the ice is thin and its layers upturned” (T.C. Chamberlin and R.D. Salisbury, Geology, Processes and their Results). Eskers are to be distinguished from kames (q.v.).