When Greenland’s Ice Rivers Change Their Minds

Takeaway: On Greenland’s ice sheet, a winter snow plug can make a summer meltwater river abandon one hole in the ice and carve a route to another.Greenland’s summer meltwater is not just water running downhill and out to sea. Some of it dives through deep holes in the ice, reaches the bed, and can help decide how the ice sheet slides. This episode follows a field team watching blue surface streams, snow-filled channels, and sudden reroutes that show Greenland’s drainage plumbing can reorganize from one year to the next.We unpack how three neighboring surface catchments on the western Greenland Ice Sheet merged over the 2017–2019 melt seasons. The surprising culprit was ordinary winter snow: it filled old meltwater canyons, blocked previous routes, and helped steer water over low divides into new channels and different moulins—the vertical shafts that carry water down through the ice. That matters because many models treat these drainage basins and moulin locations as fairly fixed, while this study shows that some can switch, merge, and change the timing and location of water reaching the ice-sheet bed.Citation: Mejia, J., Gulley, J., Trunz, C., Breithaupt, C., and Covington, M.: Greenland supraglacial catchment consolidation by streams breaching drainage divides, The Cryosphere, 19, 6445–6460, 2025, https://doi.org/10.5194/tc-19-6445-2025.Disclosure: This Waterlines episode uses AI-generated voices for the host conversation.