Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory said that the refreezing process uplifts, distorts and warms the ice above, making it softer and easier to flow.
The structures cover about a tenth of northern Greenland, the researchers estimate, becoming bigger and more common as the ice sheet narrows into ice streams, or glaciers, headed for the sea. As meltwater at the bottom refreezes over hundreds to thousands of years, the researchers believe it radiates heat into the surrounding ice sheet, making it pick up its pace as the ice becomes softer and flows more easily.
The researchers have revealed that Greenland's glaciers appear to be moving more rapidly toward the sea as climate warms but it remains unclear how the refreeze process will influence this trend.
The study is published in Nature Geoscience.