Greenland’s Ice Drains: How Giant Moulins Change the Pressure Under an Ice Sheet

Takeaway: A moulin can act less like a drainpipe and more like a hidden water tank, softening daily pressure pulses under Greenland’s ice.Greenland’s meltwater does not just run across the surface and disappear. In summer, blue rivers plunge into holes in the ice and help decide how much water pressure builds at the bed of the ice sheet, where ice can slide faster toward the ocean. That matters for coastal communities, sea-level planning, and anyone trying to understand how a warming climate changes frozen landscapes from the inside out.In this episode of Waterlines, we explore a study that takes listeners into Greenland’s moulins: steep meltwater shafts that connect the surface of the ice sheet to its hidden drainage system below. Researchers measured water levels inside moulins, modeled how daily melt pulses move through the system, and directly explored two moulins with very different shapes. Their surprising finding: some moulins are far larger than many models have assumed, with storage spaces big enough to dampen daily pressure swings under the ice.We talk through what a moulin is, why subglacial water pressure matters for ice sliding, how a big hole can act like a water tank rather than a simple drainpipe, and why scientists still need many more observations before predicting how future melt will affect Greenland’s motion. We also discuss the field reality of studying these places: pressure sensors lowered into dark shafts, rope-access exploration, uncertainty in models, and the practical stakes for sea-level rise.Full paper citation: Covington, M. D., Gulley, J. D., Trunz, C., Mejia, J., & Gadd, W. (2020). Moulin volumes regulate subglacial water pressure on the Greenland Ice Sheet. Geophysical Research Letters, 47, e2020GL088901. https://doi.org/10.1029/2020GL088901Disclosure: This episode uses AI-generated voices for the host conversation.