Ice cap thaw may awaken Icelandic volcanoes

"The effects would be biggest with ice-capped volcanoes," she said. "If you remove a load that is big enough you will also have an effect at depths on magma production."

She and Sigmundsson wrote a 2008 paper in the scientific journal Geophysical Research Letters about possible links between global warming and Icelandic volcanoes.

That report said that about 10 percent of Iceland's biggest ice cap, Vatnajokull, has melted since 1890 and the land nearby was rising about 25 millimetres (0.98 inch) a year, bringing shifts in geological stresses.

They estimated that the thaw had led to the formation of 1.4 cubic km (0.3 cubic mile) of magma deep below ground over the past century.

At high pressures such as under an ice cap, they reckon that rocks cannot expand to turn into liquid magma even if they are hot enough. "As the ice melts the rock can melt because the pressure decreases," she said.

Sigmundsson said that monitoring of the Vatnajokull volcano since 2008 suggested that the 2008 estimate for magma generation was "probably a minimum estimate. It can be somewhat larger."

He said that melting ice seemed the main way in which climate change, blamed mainly on use of fossil fuels, could have knock-on effects on geology. The U.N. climate panel says that global warming will cause more floods, droughts and rising seas.