Moulin (geology)

Schematic drawing of glacial features illustrating how moulins transport surface water to the base of the glacier

Surface water entering a moulin on Athabasca Glacier

A moulin or glacier mill is a roughly circular, vertical to nearly vertical well-like shaft within the a glacier through which water enters it from the surface. The term is derived from the French word for mill.^[1]

They can be up to 10 meters wide and are typically found at a flat area of a glacier in a region of transverse crevasses.^[2] Moulins can go all the way to the bottom of the glacier and can be hundreds of meters deep, or may reach the depth of common crevasse formation (about 10–40 m) where the stream flows englacially.^[2] They are the most typical cause for the formation of a glacier cave.

Moulins are a part of a glacier's internal "plumbing" system, that carry meltwater from the surface down to wherever it may go.^[3] Water from moulins 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. 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 may be formed. The role of water in lubricating the base of ice sheets and glaciers is complex. Difficulties modelling this process led to apparently over-optimistic predictions of sea level rise by the IPCC in the IPCC fourth assessment report. Recent research by Stefan Rahmstorf, released at the Climate Congress suggests that sea level rise will be greater than predicted in the IPCC's report.^[4]

See also

• Firn
• Giant's kettle
• Holocene glacial retreat
• Melt pond
• Sinkhole
• Snake coils
• Subglacial lake
• Supraglacial lake

References

1. ^ 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. ISBN 0-922152-76-4
2. ^ ^{a b} "Moulin 'Blanc': NASA Expedition Probes Deep Within a Greenland Glacier". Earth Observatory. NASA. Dec 11, 2006. http://earthobservatory.nasa.gov/Newsroom/view.php?id=31613. Retrieved 2009-06-17. 
3. ^ Amos, Jonathan (Dec 21, 2008). "Explorers dive under Greenland ice". BBC News. http://news.bbc.co.uk/2/hi/science/nature/7780200.stm. Retrieved 2009-06-17. 
4. ^ Rahmstorf, S. (Apr 6, 2010). "A new view on sea level rise". Nature Reports: Climate Change (1004): 44–45. doi:10.1038/climate.2010.29. 

External links

• Earth Observatory page.
• December 2006 article about a NASA expedition to Greenland moulin.
• Moulins in Greenland (Google)