A moulin (or glacier mill) is a roughly circular, vertical (or nearly vertical) well-like shaft formed where a surface meltstream exploits a weakness in the ice. The term is derived from the French word for mill.
[Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, J.A., eds. (2005) ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ]
They can be up to 10 meters wide and are typically found on ice sheets and flat areas of a glacier in a region of transverse crevasses. Moulins can reach the bottom of the glacier, hundreds of meters deep,
or may only reach the depth of common crevasse formation (about 10–40 m) where the stream flows englacially.
They are the most typical cause for the formation of a
glacier cave.
Moulins are parts of the internal structure of glaciers, that carry
meltwater
Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing. Meltwater ca ...
from the surface down to wherever it may go.
Water from a moulin often exits the glacier at base level, sometimes into the sea, and occasionally the lower end of a moulin may be exposed in the face of a glacier or at the edge of a stagnant block of
ice.
Water from moulins may help lubricate the base of the glacier, affecting
glacial motion
Glacial motion is the motion of glaciers, which can be likened to rivers of ice. It has played an important role in sculpting many landscapes. Most lakes in the world occupy basins scoured out by glaciers. Glacial motion can be fast (up to , ob ...
. Given an appropriate relationship between an ice sheet and the terrain, the head of water in a moulin can provide the power and medium with which a
tunnel valley
A tunnel valley is a U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages. They can be as l ...
may be formed. The role of this water in lubricating the base of ice sheets and glaciers is complex and it is implicated in
accelerating the speed of glaciers and thus the rate of
glacial calving
Ice calving, also known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier.Essentials of Geology, 3rd edition, Stephen Marshak It is a form of ice ablation or ice disruption. It is the sudden release ...
.
See also
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Firn
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Giant's kettle
A giant's kettle, also known as either a giant's cauldron, moulin pothole, or glacial pothole, is a typically large and cylindrical pothole drilled in solid rock underlying a glacier either by water descending down a deep moulin or by gravel r ...
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Holocene glacial retreat
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Melt pond
Melt ponds are pools of open water that form on sea ice in the warmer months of spring and summer. The ponds are also found on glacial ice and ice shelves. Ponds of melted water can also develop under the ice.
Melt ponds are usually darker th ...
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Névé
Névé is a young, granular type of snow which has been partially melted, refrozen and compacted, yet precedes the form of ice. This type of snow is associated with glacier formation through the process of ''nivation''. Névé that survives a ...
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Sinkhole
A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...
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Snake coils
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Subglacial lake
A subglacial lake is a lake that is found under a glacier, typically beneath an ice cap or ice sheet. Subglacial lakes form at the boundary between ice and the underlying bedrock, where gravitational pressure decreases the pressure melting point ...
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Supraglacial lake
A supraglacial lake is any pond of liquid water on the top of a glacier. Although these pools are ephemeral, they may reach kilometers in diameter and be several meters deep. They may last for months or even decades at a time, but can empty in t ...
References
External links
Earth Observatory pageDecember 2006 articleabout a
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeedin ...
expedition to Greenland moulin.
Moulins in Greenland (Google)
Glaciology
Glacial landforms
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