A long, winding ridge of stratified sand and gravel deposited by streams flowing under a glacier is called an:

An esker is a long, narrow, winding ridge made of layered (stratified) sand and gravel. It is formed by meltwater streams that flowed in tunnels within, under or on top of a glacier or ice sheet.

How eskers form:

• As a glacier melts, water flows through channels in or beneath the ice, carrying sand and gravel.
• This material is deposited along the stream channel.
• When the ice finally melts away, the deposits remain as a ridge that follows the path of the old stream.

Features of eskers:

• They can be a few metres to tens of metres high and many kilometres long.
• They often wind across the landscape like a railway embankment.
• Their material is sorted and layered, because it was deposited by running water.
• Examples are found in Canada, Scandinavia, Ireland, Scotland and the northern USA, which were covered by ice sheets during the last Ice Age.

Glacial depositional landforms:

• Glaciers deposit material in two ways: directly by the ice (unsorted material called till) and by meltwater (sorted material).
• Drumlins: smooth, oval-shaped hills of till, shaped like an upside-down spoon, with the blunt end facing the direction from which the ice came.
• Outwash plains: broad plains of sand and gravel deposited by meltwater streams in front of a glacier.
• Kames and kettle holes: mounds of sand and gravel and depressions left by melting blocks of ice.
• Another important type of glacial deposit, made of unsorted rock debris directly dropped by the ice, is covered in a separate question.

Glacial erosional landforms:

• Cirques (corries): armchair-shaped hollows at the head of a glacial valley.
• U-shaped valleys and hanging valleys.
• Horns: pyramid-shaped peaks, such as the Matterhorn.

Why not the other options?

• ✗A drumlin is an oval hill of glacial till.
• ✗A cirque is a bowl-shaped hollow eroded by a glacier.
• ✗A kame is an irregular mound of sand and gravel, not a long winding ridge.