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How do flutes form beneath glaciers?
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glacial landform
Eskers,
or narrow
ridges of
gravel and sand left by a retreating glacier,
wind through western
Nunavut, Canada, near the Thelon River.
Flutes are depositional glacial landforms that form beneath glaciers, particularly near their lower margins where the ice glides over a bed of pressurized, muddy till.1
The formation process occurs as follows:
- Obstacle Encounter: As the basal ice flows around a pronounced bedrock knob or a boulder lodged in the substrate, the high viscosity of the ice causes a cavity to form on the lee (down-ice) side of the obstacle.1
- Injection and Deposition: The pressurized, muddy subglacial paste is injected into this cavity.1
- Result: This material is deposited as an elongate tail of till, known as a flute.1
The dimensions of a flute—which can range from a few centimetres to tens of metres in height and from tens of centimetres to kilometres in length—depend primarily on the size of the obstacle and the availability of subglacial debris. While they are common features in areas covered by ground moraine, very large flutes are generally limited to continental ice sheets.12