An esker is formed when there is a sub-glacial meltwater channel flowing within the body of the glacier and sediment is deposited within this channel. After the ice age when the glacier melts, a ridge of sediment is left behind representing where the previous meltwater tunnel deposits descended to the valley floor as the surrounding ice melted. It looks like a winding ridge that follows the general route of the glacier and consists of coarse sand and gravel and visually, may be likened to a medial moraine. However, it is distinguished by more rounded, less angular material and a degree of sorting of deposits with heavier gravels lower down and sandy material higher up.