Moulins are gigantic, nearly-vertical shafts that carry meltwater from the surface of a glacier to the base of the glacier, where the water can affect ice flow. To date, it is possible to observe the openings of moulins from space (Figure 1), and — in some exceptional instances — to send bold and highly skilled human explorers into moulins (Figure 2), where they can map the top few tens to hundreds of meters of the moulin. But Greenland moulins can be 500 – 1000 meters deep, and what lies beneath the near surface is not known. Thus, we quantified the most important processes that change the size and shape of a moulin over time and combined them into a model.
The Moulin Shape (MouSh) model was jointly developed by myself, Celia Trunz (UB-GML alum), and Lauren Andrews (NASA-GSFC researcher). We described the model and its first results in Andrews, Poinar, and Trunz (2022), freely available in The Cryosphere.
Moulins in Pakitsoq, western Greenland. On the left, the orange dot is a moulin location in 2012, and the surrounding seven white dots show how that moulin has moved around over 2009-2017. The water in the skinny blue lake is flowing downhill towards the left. On the right, the sites of a few hundred moulins (light blue) found in Pakitsoq. The dark blue lines show the subglacial water routing – the path the water takes after it reaches the base of the moulin.A selection of maps and photos from inside moulins. To date, humans have been able to explore the top few hundred meters of moulins in August – October, toward the end of the melt season, when it is safer to do so!
How important are moulins to the journey of meltwater to the ocean?
Moulins (vertical shafts) comprise about 10% of the total length of the water flow paths through and under glaciers (all blue lines).
How much do moulins change shape over time?
The effects of three modes of moulin shape change — viscous deformation (blue), elastic deformation (red), and melting/freezing (green) — on five moulins in glaciers with different thicknesses (panels a-e). These processes change the size and shape of the moulin by ~20% every day (panel g). From Andrews, Poinar, & Trunz (2022)..
