Giant ice structures, as tall as skyscrapers, have been identified under the ice sheets of Greenland. Some of these gigantic towers are as wide at the base as Manhattan. The existence of these skyscrapers of ice was discovered using ice-penetrating radar.
Researchers believe these structures were formed as underground water froze and expanded, lifting the ice sheet above it. This could also make it easier for glaciers to travel.
"We think the refreezing process uplifts, distorts and warms the ice above, making it softer and easier to flow," Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory, said.
Bell and her team believe the skyscrapers of ice cover up to one-tenth of northern Greenland.
These towers become larger and more common as the ice sheet narrows into glaciers and the ice moves toward the open water. As this happens, meltwater under the ice sheet re-freezes, releasing its heat into the surrounding ice sheets. This partially melts the glacier, accelerating its progress to the open water.
Evidence for these giant structures has been seen by scientists since the 1970's, but investigators previously believed they were hills composed of rock and dirt.
IceBridge, a program measuring ice loss in Polar Regions, recognized the protrusions as being composed of ice. Bell immediately recognized the features, having previously discovered similar structure in the ice sheet and East Antarctica.
Steep valley walls and ridges in the Gamburtsev Mountains of Antarctica show evidence of widespread melting and re-freezing of water deposits. Petermann Glacier in northern Greenland made headlines in 2010, when a block of ice 100 square miles in size broke off the frozen channel.
Basal sliding is the term applied to glaciers sliding toward the water, aided by slushy meltwater underneath the frozen river.
"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," Joseph MacGregor of the University of Texas wrote in an accompanying letter to Bell's article.
Study of the ice towers could help climatologists and environmentalists better predict how different phases of water can interact in Earth's Polar Regions. This information can be used to create more accurate models of future environmental conditions.
Researchers say the glaciers of Greenland are sliding ever more quickly into the sea, but they are uncertain how the towers affect the migration.
Discovery of towers of ice under the Greenland ice sheet was detailed in the journal Nature Geoscience.