Melting ice spells volcanic trouble

http://www.newscientist.com/article/dn26923-melting-ice-spells-volcanic-trouble.html#.VVpzzPAYFB8

by Fred Pearce
Feb. 5, 2015

Melting ice is causing the land to rise up in Iceland – and perhaps elsewhere. The result, judging by new findings on the floor of the Southern Ocean, could be a dramatic surge in volcanic eruptions.

Last week, researchers at the University of Arizona in Tucson showed that a recent dramatic uplift of the Earth's crust in parts of Iceland coincided with the rapid melting of nearby glaciers.

Kathleen Compton's team used data from GPS receivers that have been attached to rocks since 1995 to show that some parts of south-central Iceland, where five of the country's largest glaciers are melting fast, have been rising by around 3.5 centimetres a year. Away from the glaciers, the rates of land rise were much lower.

Their explanation is that the disappearance of the ice is relieving pressure on rocks beneath and allowing them to spring up.

It has long been known that the Earth's crust falls and rises as ice caps grow and melt. But the speed of the rebound is surprising, says Compton.

Richard Katz of the University of Oxford finds the discovery "very exciting". "The measurements show that there is a response even at a very short time-scale of 30 years," he says.

The land uplift could be handy to protect some coastal areas from rising sea levels as the melting ice flows into the oceans. But there is a growing fear among geologists that climate-induced changes to water and ice levels could trigger more dangerous events, such as volcanic eruptions.

The evidence is mostly from the past. For instance, during the last great melt 12,000 years ago, volcanic activity on Iceland was up to 50 times greater than the activity observed over the past century, says Bill McGuire, a volcanologist at University College London. Iceland has suffered three major volcanic eruptions in the past five years – although no one has shown a certain link with climate change.

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So it seems that glaciation can trigger submarine eruptions, while deglaciation may lead to magma outflows on land.

"Both these studies reinforce the idea that the wholesale redistribution of water that accompanies major climate change elicits a significant response from the solid earth in the form of potentially hazardous phenomena such as earthquakes and volcanic eruptions," says McGuire. "We saw this very dramatically at the end of the last ice age, and we are seeing it again today in Iceland and elsewhere."