Glacier Moulins
What is a Moulin?
Moulin, a French word for “mill”, is a vertical rivers that serve as a glacier’s internal plumbing system. They carry water out of the glacier through meltwater streams and lakes formed on the surface of the ice.
These shafts provide a pathway for water to flow from the glacier’s surface to its base. Similar to how rainwater erodes the bedrock on the Earth’s crust to form sinkholes, summer meltwater on a glacier’s surface erodes ice and creates moulins.
The warmer summer temperatures create lakes and streams on the glacier’s surface.
This water then drains, following the path of least resistance. Eventually, these streams will find a crevasse or other weak spot in the ice and begin to pour into it. As water moves downward, turbulence and heat create a vertical shaft that can extend all the way to the bottom of the glacier and create additional pathways. These pathways can be hundreds of feet deep.
Moulin Movements
The flowing water will exit the glacier at its base, where it acts like a lubricant between the ice and the bedrock. The melting water accelerates the glacier’s flow in summer. Meltwater in the summertime allows the Matanuska to flow up to one foot per day.
Once formed, the shaft will remain open as long as meltwater continues to flow. In winter, as the water freezes, the moulin will begin to fill up with ice and snow and close up. Moulins often occur in the same spot for multiple years. However, the place will continue to move forward with the flow of the ice. As the glacier continues to melt, these large drainages will eventually reach the surface.
So if you ever find yourself traversing the ice, be sure to keep an eye out for moulins. Some are small wonders to peer into and imagine the intricacy within. Others will astound you with their immensity and grandeur. Either way, with the help of meltwater, the moulin world is constantly changing.
Author: Quinn Zinkievich
