Eskers

An esker is a landform that records the final act of a glacier's life — the meltwater. When a glacier melts, the water does not simply vanish; it organises itself into streams that flow beneath the ice, and the debris those streams carry is left behind as a long, winding ridge once the ice is gone.

The story begins with summer melting. Water from the melting ice flows in three possible ways: over the glacier's surface, down along its margins, or straight through holes in the ice body itself. All this water eventually collects beneath the glacier, where it moves like an ordinary stream in a channel. The crucial point is that this channel is not cut into the ground — it is a channel whose floor is the ground but whose banks are made entirely of ice.

Because the stream flows with ice for its banks, it behaves differently from a normal river. It carries very coarse material — boulders and blocks — along with smaller rock fragments. When the stream's energy drops, this heavy load settles out and gets deposited in the valley of ice beneath the glacier. Later, when the glacier melts away completely, that deposit is exposed. What remains is a sinuous, winding ridge of coarse sediment, and that ridge is the esker.

• Source of water: summer meltwater from the glacier surface, margins, or holes in the ice.
• Path of flow: water gathers beneath the glacier and flows as a stream in an ice-walled channel.
• Channel nature: the stream flows over the ground, not in a valley cut into the ground; the ice itself forms the banks.
• Material carried: very coarse debris — boulders and blocks — plus some finer rock fragments.
• Deposition: the coarse load settles in the ice-walled channel beneath the glacier.
• Final landform: after the ice melts, the deposit appears as a sinuous ridge — the esker. …