Northeast-looking oblique aerial photograph of several meandering eskers and other glacially-produced sedimentary features, adjacent to the margin of the retreating Casement Glacier, St Elias mountains, Glacier Bay National Park, Alaska.
An esker is a meandering, water-deposited, generally steep-sided ridge of glacial drift that forms within a subglacial or englacial stream channel. Its floor can be bedrock, sediment, or ice. Subsequent melting of the glacier exposes the deposit. Generally composed of stratified sand and gravel, eskers can range from meters to several kilometers in length and may exceed 30 m in height.