What is an Esker?

What is an Esker?

• A. A dune formed by wind
• B. Steep sided winding ridge of till
• C. A layer of limestone
• D. An underground river

Answer: (B)

Eskers are long, winding ridges that form when meltwater rivers run through or under a glacier. As the ice flows/retreats, these subglacial streams carry and then deposit sand and gravel in their channels, creating a layered, well-sorted ridge that often sticks up above the surrounding landscape after the ice disappears. This is different from wind-blown dunes (which are shaped by air), a limestone layer (a rock type, not a sediment deposit), or an underground river (water that stays beneath the surface without leaving a raised, layered ridge). Eskers consist of sorted sediments laid down by water, not the unsorted debris of glacial ice (till).

Eskers are long, winding ridges that form when meltwater rivers run through or under a glacier. As the ice flows/retreats, these subglacial streams carry and then deposit sand and gravel in their channels, creating a layered, well-sorted ridge that often sticks up above the surrounding landscape after the ice disappears. This is different from wind-blown dunes (which are shaped by air), a limestone layer (a rock type, not a sediment deposit), or an underground river (water that stays beneath the surface without leaving a raised, layered ridge). Eskers consist of sorted sediments laid down by water, not the unsorted debris of glacial ice (till).