Fragmented ice floes near the coast of West Antarctica
Space agency believes it has finally found the source of the mysterious heat warming the polar cap

There is something mysterious and hot lurking beneath the surface of the Antarctic ice.

Now Nasa says that it might have found the source of that strange heating - a "mantle plume" - or upwelling of abnormally hot rock, that lies deep beneath the surface.

The heat is causing the surface of the ice to melt and crack, resulting in rivers and other disruption to Antarctica.

Around 30 years ago, a scientist at the University of Colorado Denver said that there might be a mantle plume under a region of the continent known as Marie Byrd Land. That hypothesis helped explain some strange features seen on the ice, like volcanic activity and a dome.

Mantle plumes are narrow streams through which hot rock rises up from the Earth's mantle, and then spreads out under the crust. Because the material itself is hot and buoyant, it makes the crust bulge upwards.

They explain how some places - like Hawaii and Yellowstone - have huge amounts of geothermal activity despite being far from the edge of a tectonic plate.

But it was also an idea that was hard to believe, since the ice above the plume is still there. "I thought it was crazy," said Helene Seroussi of Nasa's Jet Propulsion Laboratory, who helped the lead work. "I didn't see how we could have that amount of heat and still have ice on top of it."

Now scientists have used the latest techniques to support the idea. The team developed a mantle plume numerical model to look at how much geothermal heat would be needed to explain what is seen at Marie Byrd Land, including the dome and the giant subsurface rivers and lakes present on Antarctica's bedrock.

They compared the theoretical model with data brought back from Nasa's missions over the Antarctic, to ensure it was realistic. It led them to believe there was a mantle plume, packed with huge amounts of pressure and heat, beneath the surface. It would have formed 50 million to 110 million years ago, long before the ice sheet itself came into being.