Greenland glaciers: what lies beneath.

• Position: Geophysics

The water flowing beneath the ice of Greenland's glaciers plays a much more complex role than previously imagined by scientists. Researchers had thought that meltwater simply lubricated ice against the bedrock, speeding the flow of glaciers out to sea. New studies reveal that the effect of meltwater on acceleration and ice loss--through fast-moving outlet glaciers that connect the inland ice sheet to the ocean--is much more complex, as a kind of plumbing system evolves over time at the base of the ice, expanding and shrinking with the volume of meltwater.

As ice melts, water trickles down into the glacier through crevices large and small, eventually forming vast rivers and lakes under the ice, explains Ian Howat, assistant professor of earth sciences at Ohio State University, Columbus. "We've come to realize that...