Sea-Level Changes Drive Variability in Volcanism

"Sea-level changes, which are a result of climate change, are what drive variability in volcanism. They do this by changing the over-pressure on the lithosphere."--Ben Lawson of "Wott's Up With That?" (4-17-10)

Ben Lawson has a site called "Wotts Up With That?" His site debunks the pseudo-scientific posts of the global warming denialist blogger Anthony Watts who has a blog called Watt's Up With That?

The global warming denialist Anthony Watts (4-16-10) is ridiculing Scientific American (4-16-10) for explaining that melting ice may contribute to volcanic eruptions in the future.

Wott's Up (4-16-10) comments:

We knew, it was only a matter of time…“. Anthony Watts sneers at Scientific American, with a side dish of Goreophobia, for suggesting that thawing ice caps in Iceland many trigger future volcanic eruptions.

I suggest Anthony and his pseudo-geologist friends Google “isostatic rebound” [see here]. It’s not likely to be a big factor, but it’s also not just theoretical.

Wikipedia explains:

Post-glacial rebound (sometimes called continental rebound, isostatic rebound, isostatic adjustment or post-ice-age isostatic recovery) is the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, through a process known as isostasy. It affects northern Europe (especially Scotland, Fennoscandia and northern Denmark), Siberia, Canada, and the Great Lakes of Canada and the United States.

Scientific American (4-16-10) notes:

A thaw of Iceland's ice caps in coming decades caused by climate change may trigger more volcanic eruptions by removing a vast weight and freeing magma from deep below ground, scientists said on Friday.

They said there was no sign that the current eruption from below the Eyjafjallajokull glacier that has paralysed flights over northern Europe was linked to global warming. The glacier is too small and light to affect local geology.

"Our work suggests that eventually there will be either somewhat larger eruptions or more frequent eruptions in Iceland in coming decades," said Freysteinn Sigmundsson, a vulcanologist at the University of Iceland.

"Global warming melts ice and this can influence magmatic systems," he told Reuters. The end of the Ice Age 10,000 years ago coincided with a surge in volcanic activity in Iceland, apparently because huge ice caps thinned and the land rose.

"We believe the reduction of ice has not been important in triggering this latest eruption," he said of Eyjafjallajokull. "The eruption is happening under a relatively small ice cap."

Carolina Pagli, a geophysicist at the University of Leeds in England, said there were risks that climate change could also trigger volcanic eruptions or earthquakes in places such as Mount Erebus in Antarctica, the Aleutian islands of Alaska or Patagonia in South America.

"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."

...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 science journal Nature (9-17-09) also has published an article titled "Volcanoes stirred by climate change."