The Heat Is Online

Glacial Melt Triggers Earthquakes

Climate change could cause earthquakes and volcanic eruptions, scientists say

 

Canadian Press, July 05, 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.

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."

 

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."

 

How Melting Glaciers Alter Earth's Surface, Spur Quakes, Volcanoes
Wall Street
Journal, June 9, 2006

Imagine the surface of Earth as a giant trampoline that accumulated a slab of ice over the winter, and you can get a sense of what a growing number of scientists say is in store for the planet as glaciers keep melting.

Once the trampoline's ice turns to water that drips over the edges in the warm days of spring, the concave elastic slowly rebounds to its original flat shape. That's how Earth responds as glaciers retreat, and the consequences promise to be ... interesting.

The reason is that one cubic meter of ice weighs just over a ton, and glaciers can be hundreds of meters thick. When they melt and the water runs off, it is literally a weight off Earth's crust. The crust and mantle therefore bounce back, immediately as well as over thousands of years. That "isostatic rebound," according to studies of prehistoric and recent earthquakes and volcanoes, can make the planet's seismic plates slip catastrophically, and cause magma chambers that feed volcanoes to act like bottles of shaken seltzer.

"It's unavoidable that glacial retreat will induce tectonic activity," says geoscientist Allen Glazner of the University of North Carolina, Chapel Hill.

The connection between melting glaciers and earthquakes isn't to be confused with a myth that zipped through cyberspace after the 2004 Asian tsunami. It claimed that global warming (which is not even two degrees above historical averages so far) heated magma, causing seismic plates to shift. No.

Instead, the world-wide melting of glaciers portends a seismically active future because of isostatic rebound and also because the meltwater from liquefying glaciers adds mass atop oceanic plates. That creates a teeter-totter effect, further destabilizing the planet's crust. "Recent findings reinforce the idea that the solid earth and the climate are inextricably linked," says Prof. Glazner.

That link has reared its ugly head in the past, especially during periods of rapid climate change such as the end of ice ages. When ice sheets retreated 10,000 years ago, for instance, Iceland experienced a surge in volcanic eruptions. Volcanoes in the Mediterranean, Antarctica and eastern California also seem to have been awakened by retreating ice.

When he analyzed 800,000 years of activity from about 50 volcanoes in eastern California (the age of rocks formed from volcanic ash can be determined by radioactive dating), Prof. Glazner found that "the peaks of volcanic activity occurred when ice was retreating globally. At first I thought it was crazy, but other scientists also found evidence that climate affects volcanism." The likely mechanism: glacial retreat lifts pressure that had kept the magma conduit closed.

The retreat of ice sheets 10,000 years ago also triggered a wave of powerful earthquakes in Scandinavia. Since isostatic rebound continues for thousands of years, it may still be contributing to quakes in eastern Canada, says geoscientist Patrick Wu of the University of Calgary.

That area has no plate boundaries, the usual site of quakes. But 9,000 years ago, when glaciers retreated, the region began experiencing frequent "intraplate" quakes up to magnitude 7, he finds. They continue to this day, with quakes such as the 6.3 Ungava event that struck northern Quebec on Christmas Day 1989.

"The pressure of the ice sheet suppresses earthquakes, so removing that load triggers them," says Prof. Wu. That creates weakened zones that remain vulnerable to seismic activity to this day, including in northern Europe. "Present-day earthquakes may have their origin in postglacial rebound," he says.

In southwest Alaska, where the Pacific plate thrusts under the continental plate, the immense mass of glacial ice counters the tendency of the plates to slip catastrophically. As global warming melts the glaciers, however, the ice load is diminishing. As a result, Earth is springing back there, too, removing the check on seismic activity. The magnitude 7.2 temblor that shook the area in 1979 is linked to a bounce-back of the crust, conclude geoscientists Jeanne Sauber of NASA's Goddard Space Flight Center and Bruce Molina of the U.S. Geological Survey.

"In southwest Alaska, glaciers have been thinning and retreating by hundreds of meters for 100 years," says Dr. Sauber. "Huge ice loads suppress earthquakes for a while, but when you remove the ice it is easier for them to occur." She therefore calls them "promoted" earthquakes. Glacial retreat, she says, "is another factor that has to be looked at when we assess seismic hazard."

Alaska isn't the only place where glacial retreat due to the current warming coincides with active faults. It does so in the Andes, the Swiss Alps, the New Zealand southern Alps, the Rocky Mountains, the Himalayas and the edges of Greenland (where scientists recently reported that the melting of the ice sheet has accelerated), says geologist Bill McGuire of University College London.

He wrote in the magazine New Scientist that "it shouldn't come as a surprise that the loading and unloading of the Earth's crust by ice or water can trigger seismic and volcanic activity." He told me that "no one knows how much unloading there can be before you trigger certain faults."