Washington, Nov 8 (IANS): A geothermal heat source called a mantle plume lies deep below West Antarctica, explaining some of the melting that creates lakes and rivers under the ice sheet, confirms a new NASA study.

The heat source may help explain why the West Antarctic ice sheet collapsed rapidly in an earlier era of rapid climate change, and why it is so unstable today, said the study published in the Journal of Geophysical Research: Solid Earth.

The stability of an ice sheet is closely related to how much water lubricates it from below, allowing glaciers to slide more easily.

Understanding the sources and future of the meltwater under West Antarctica is important for estimating the rate at which ice may be lost to the ocean in the future.

The mantle plume deep below Antarctica's Marie Byrd Land formed 50 to 110 million years ago, long before the West Antarctic ice sheet came into existence, the researchers determined.

At the end of the last ice age around 11,000 years ago, the ice sheet went through a period of rapid, sustained ice loss when changes in global weather patterns and rising sea levels pushed warm water closer to the ice sheet -- just as is happening today.

The researchers suggest that the mantle plume could facilitate this kind of rapid loss.

Some 30 years ago, a scientist at the University of Colorado Denver suggested that heat from a mantle plume under Marie Byrd Land might explain regional volcanic activity and a topographic dome feature.

Very recent seismic imaging has supported this concept.

When Helene Seroussi of NASA's Jet Propulsion Laboratory in Pasadena, California, first heard the idea, however, "I thought it was crazy," she said.

"I didn't see how we could have that amount of heat and still have ice on top of it," Seroussi said.

With few direct measurements existing from under the ice, Seroussi and Erik Ivins of JPL concluded the best way to study the mantle plume idea was by numerical modelling.

They used the Ice Sheet System Model (ISSM), a numerical depiction of the physics of ice sheets developed by scientists at JPL and the University of California, Irvine.

To assure the model was realistic, the scientists drew on observations of changes in the altitude of the ice sheet surface made by NASA's IceSat satellite and airborne Operation IceBridge campaign.

Since the location and size of the possible mantle plume were unknown, they tested a full range of what was physically possible for multiple parameters, producing dozens of different simulations.

They found that the flux of energy from the mantle plume must be no more than 150 milliwatts per square metre.

For comparison, in US regions with no volcanic activity, the heat flux from Earth's mantle is 40 to 60 milliwatts.