Researchers discovered a process of melting and refreezing that could change the way we understand ice sheet behavior.
Using ice-penetrating radar scientists discovered blocks of ice as tall as city skyscrapers and as wide as the island of Manhattan, an Earth Institute at Columbia University news release reported.
The structures may have formed when water beneath the sheet refroze and "warped upwards."
"We see more of these features where the ice sheet starts to go fast," the study's lead author, Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory, said in the news release. "We think 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 and are becoming larger and more common as the ice sheet narrows into glaciers headed for the sea.
In the past radio images of these structures were mistaken for hills, but more advanced NASA instruments showed they were made up of ice instead of rock.
The researchers found extensive melting and refreezing along the ridges in the range could deform the "layer-cake" structure above it. This means the sheets can grow from the bottom up.
The researchers looked at Greenland's Petermann Glacier, which let a 100-square-mile chunk of ice get away back in 2010. They found the glacier is sweeping large features with it towards the coast twice as quickly as neighboring ice.
The researchers believe the refreeze process influences the glacier's advance.
"Overall, these observations suggest that basal freeze-on is a key control on the large-scale flow of Petermann Glacier, a possibility that has not been explored previously," University of Texas researcher Joseph MacGregor said in the news release.
Greenland's glaciers appear to be moving more quickly towards the ocean in general, but it is unclear if the refreeze process will have an effect on the trend. The findings sugges that deformation at the base of the ice sheet is more widespread than previously believed.
"When you're flying over this flat, white landscape people almost fall asleep it's so boring-layer cake, layer cake, layer cake," study coauthor Kirsty Tinto, a geophysicist at Lamont-Doherty, said in the news release. "But then suddenly these things appear on the screen. It's very exciting. You get a sense of these invisible processes happening underneath."
