Eskers are sinuous ridges composed of glacifluvial sand and gravel. They are deposited in channels with ice walls in subglacial, englacial and supraglacial positions. Eskers have been observed widely in deglaciated terrain and are varied in their planform. Many are single continuous ridges, whereas others are complex anastomosing systems and some are successive subaqueous fans deposited at retreating tidewater glacier margins (Benn & Evans 2010). Eskers are usually orientated approximately in the direction of past glacier flow. When basal water flows under pressure in full conduits, the hydraulic gradient and direction of water flow are controlled primarily by ice-surface slope, with bed topography of secondary importance (Shreve 1985). In such cases, eskers typically record the former flow of channelized and pressurized water both up- and downslope.