An esker is a long, winding ridge of gravel and other sedimentary material that was deposited by a subglacial or englacial meltwater stream. OSAR is an acronym for 'Oscillating Streams and Associated Ridges', which is another name for eskers. Eskers are typically found in areas where glaciers have recently melted, such as in the Arctic and Antarctic regions. They are also found in North America, Europe, and Asia.