When Greenland’s Meltwater Slows the Ice

Takeaway: A sudden flood under Greenland’s ice can drain hidden water pockets at the bed, making the ice grip harder and slow down even while meltwater keeps flowing.Greenland’s summer melt does more than make rivers on the ice surface; it can change how the whole ice sheet grips the ground below. That matters because the speed of Greenland’s ice helps shape future sea level, coastal planning, and the way climate change shows up far from the Arctic. In this episode, we follow scientists to a moulin—a deep vertical drain in the ice—and listen as a hidden floodwave from draining surface lakes rushes under the ice sheet. The surprise: the flood did not simply carve bigger plumbing and speed things along. It appears to have drained hidden pockets of pressurized water at the bed, helping the ice stick more firmly and slow down to winter-like speeds. We unpack what moulins are, how researchers measure water pressure and ice motion in a dangerous, shifting landscape, and why Greenland may not behave like the smaller mountain glaciers scientists often use as examples. Citation: Mejia, J. Z., Gulley, J. D., Trunz, C., Covington, M. D., Bartholomaus, T. C., Xie, S., & Dixon, T. H. (2021). Isolated cavities dominate Greenland Ice Sheet dynamic response to lake drainage. Geophysical Research Letters, 48, e2021GL094762. https://doi.org/10.1029/2021GL094762. Disclosure: This Waterlines episode package is written for AI-generated host voices; the voices listeners hear are AI-generated.