What Is a Moulin?
A moulin (French for “mill”) is a narrow, tubular chute, hole or crevasse worn in the [glacial] ice by surface water, which carries water from the surface to the base far below. 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. These holes 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 10-40m) where the stream flows englacially.
These holes are a part of a glacier’s internal “plumbing” system, to carry melt water out to wherever it may go. Water often exits the glacier at base level, but 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.
The cascading water through the ice pushes down on the glacier at the same time water seeps through cracks to the underside. In this way, water becomes a lubricating fluid at the base of the glacier, enhancing glacial motion and speeding disintegration of the ice sheet. The melting water encourages further ice loss and accelerates the glacier’s flow to the sea, where large chunks break off to form icebergs.
Decreasing sea ice at the Poles is deeply concerning scientists, as it has an important function in moderating the global energy balance. Sea ice has albedo of 0.8 which means it reflects 80% of the suns rays, but When the sea ice melts to form water the albedo is only 0.2. In other words, the highly reflective sea ice goes from absorbing 20% of the sun’s rays to absorbing 80%, creating a positive feedback for further warming.
courtesy of: http://www.global-greenhouse-warming.com/moulin.html