Instead of solid ice, the sheet is riddled with gaps through which water surges.
This may help to explain the speed at which the ice is melting, said Dr. Konrad Steffen, of the University of Colorado, who announced the discovery at a climate change conference this week in Copenhagen.
Nasa scientists helped to design the camera lowered into a moulin — a hole in the ice — to see what lay hundreds of metres beneath the surface. The 10m wide moulin acted as a conduit for fast-flowing meltwater streams on the top of the ice.
The camera, combined with images from ground-penetrating radar equipment, uncovered a network of tunnels which channel the water through the ice.
“The whole ice sheet is connected with these open channels,” Dr. Steffen said. He also explained that the moulin becomes much wider, about 50 metres across, soon after plunging away from the surface.
Dr. Steffen believes that the channels in the ice play a role in the sharp increases in ice movement during the summer. Meltwater that would otherwise remain on the surface could, once it reaches the bedrock, lubricate the movement of the ice towards the sea where it would melt and contribute to sea level rises.
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