July 4, 2006

Climate change could cause earthquakes and volcanic eruptions, scientists say

Canadian Press
By: DENNIS BUECKERT
July 4, 2006

OTTAWA (CP) - So the warnings of harsher heat waves, stronger hurricanes and rising seas fail to impress. How about volcanic eruptions in the Arctic, or a tsunami off the coast of Newfoundland?

The latest scientific discipline to enter the fray over global warming is geology.

And the forecasts from some quarters are dramatic - not only will the earth shake, it will spit fire.

A number of geologists say glacial melting due to climate change will unleash pent-up pressures in the Earth's crust, causing extreme geological events such as earthquakes, tsunamis and volcanic eruptions.

A cubic metre of ice weighs nearly a tonne and some glaciers are more than a kilometre thick. When the weight is removed through melting, the suppressed strains and stresses of the underlying rock come to life.

University of Alberta geologist Patrick Wu compares the effect to that of a thumb pressed on a soccer ball - when the pressure of the thumb is removed, the ball springs back to its original shape.

Because the earth is so viscous the rebound happens slowly, and the quakes that occasionally shake Eastern Canada are attributed to ongoing rebound from the last ice age more than 10,000 years ago.

Human impact will speed process
Melting of the ice that covers Antarctica or Greenland would have a similar impact, but the process would be accelerated due to the human-induced greenhouse effect.

"What happens is the weight of this thick ice puts a lot of stress on the earth," says Wu. "The weight sort of suppresses the earthquakes but when you melt the ice the earthquakes get triggered."

When a quake happens under water it can cause a tsunami. Wu said melting of the Antarctic ice is already causing earthquakes and underground landslides although they get little attention. He predicted climate warming will bring "lots of earthquakes."

When the glaciers melt, the reliquified water causes sea levels to rise and increases the weight on the ocean floor, which could also have an effect on the grinding tectonic plates deep below the surface.

The Earth's crust is more sensitive than some might think. There are well-documented cases of dams causing earthquakes when the weight of the water behind a dam fills a reservoir.

Alan Glazner, a volcano specialist at the University of North Carolina, said he was initially incredulous when he found a link between climate and volcanic activity off the coast of California.

"But then I went to the library and did some research and found that in many places around the world especially around the Mediterranean they see similar sorts of correlations."

"When you melt glacial ice, several hundred metres to a kilometre thick . . . you've decreased the load on the crust and so you've decreased the pressure holding the volcanic conduits closed.

"They're cracks, that's how magmas gets to the surface . . . and where they hit the surface, that's where you get a volcano."

New interest in climate-change link
No one has claimed that the Christmas tsunami of 2004 was triggered by rising sea levels. But that event seems to have sparked new interest in the links between climate and geology. "All over the world evidence is stacking up that changes in global climate can and do affect the frequencies of earthquakes, volcanic eruptions and catastrophic sea-floor landslides," says British geologist Bill McGuire, writing in New Scientist magazine.

"Not only has this happened several times throughout Earth's history, (but) the evidence suggests it is happening again," says McGuire, professor of geological hazards at University College in London.

Glazner said the main impact of glacial melting is due to reduced weight on the places losing glaciers rather than the increased weight on the ocean floor.

"If you melt that glacier and the water runs into the oceans, that water is spread over the entire surface of the ocean and it might add a millimetre to the thickness of the oceans or something, but you've taken a kilometre off of that place where the glacier used to be."