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Fire, ice and climate change

Rahul Goswami / 25 April 2010

Here’s a back of the envelope calculation that adds a whole new dimension to the impacts of climate change. A geologist in North America has estimated that the Canadian ice sheet, which is both very thick and spreads across many thousands of square kilometres, must weigh 80-100 million billion tonnes. It’s a sum too large to contemplate even for those used to gauging loading speeds for, say, very large crude oil carriers.

What happens when this ice sheet melts?

That is the question which many geologists have begun to ask one another in the wake of the eruption of Iceland’s Eyjafjallajökull volcano on March 20, 2010, which awakened after 120 years, spewing lava fountains and flows.

Did the lightening of the ice sheets’ load of the north (even by a small fraction) release some of the pressure on the tectonic plates? According to a new set of scientific papers published by Britain’s Royal Society, there is indeed a connection. “Periods of exceptional climate change in Earth history are associated with a dynamic response from the solid Earth, involving enhanced levels of potentially hazardous geological and geomorphological activity,” said the introduction to a set of scientific papers on the subject.

The material put out by the Royal Society also points to the European Alps becoming a hazardous zone. A scientist has warned that warm temperature extremes in Europe can set off large landslides in temperature-sensitive high mountains by causing more snow and ice to melt, and by rapid thaw. There are already findings that a number of “large slope failures” in some high-mountain regions such as the European Alps has increased during the past two to three decades, leading to concern that climate change is the cause.

“Looking ahead,” observes the Royal Society summery, “modelling studies and projection of current trends point towards increased risk in relation to a spectrum of geological and geomorphological hazards in a world warmed by anthropogenic [human induced] climate change, while observations suggest that the ongoing rise in global average temperatures may already be eliciting a hazardous response from the geosphere.”

There has been evidence brought out in the past decade of climate change research that glaciers and ice sheets on many active volcanoes are rapidly receding. There is also compelling evidence that the planet-wide melting during the waning of the last ice age triggered a dramatic acceleration in volcanic activity. Now scientists are saying that global warming could set off ruptures and seismic shifts because of the way it can move large amounts of mass around on the Earth’s surface. Melting glaciers and rising sea levels shift the distribution of huge amounts of water, which release and increase pressures through the ground.

These are after all the laws of physics which are hard to skirt. Change the load, either up or down, and the stress on underlying structures changes. Vulcanologists say that pressure influences both magma production and the structural failure of magma chambers. That’s why the reduction in ice load on sub-glacial volcanoes due to global warming is changing pressure conditions under the surface of the earth. Iceland’s ice caps have been thinning since 1890 which has led to what earth scientists call “glacial rebound” (which simply means the earth’s crust springing back as pressure on it from above is lessened) at rates exceeding 20mm per year.

What becomes of Iceland now? Worryingly, models predict a significant amount of new magma generation under Iceland due to ice retreat.

Almost unnoticed against the frustration of thousands of air travellers stranded by the volcanic cloud from Eyjafjallajökull was another event which has become one of the more familiar manifestations of climate change. A huge section of a glacier in mountainous Peru broke off and crashed into a lake, setting off a massive wave that destroyed a nearby town.

The local governor of the region in Peru, Cesar Alvarez, told media that global warming would cause glaciers in his country “to detach and fall on these overflowing lakes”. We have become accustomed to reading about the Antarctic ice sheets melting and calving icebergs, with no immediate impact on human settlements, but when the same action (on a much smaller scale) takes place in inhabited highlands, the human cost is high.

China’s enormous Three Rivers Gorge dam is an example of increasing load on the Earth’s crust. There has been speculation that the Sichuan quake (7.9 magnitude) which killed about 80,000 people was triggered by the filling behind the dam. Officials in China have acknowledged that seismic activity has increased slightly since the 640 kilometre long reservoir began filling eight years ago, but the link between water storage on a gigantic scale and quakes was noticed much earlier.

There was evidence in 1945 of the effects of loading the crust with massive new weight. That is when scientists discovered — ten years after the Hoover Dam in the US was built in 1935 — that its reservoir was increasing seismic activity. Since then, it has been well established that other human activities can set off powerful tremors beneath the earth’s surface. These include coal mining, quarrying, oil drilling, and the injection of wastewater into the ground. Research from Germany also suggests that the earth’s crust can sometimes be so close to failure that relatively tiny changes in surface pressure, such as that caused by torrential rain, can also trigger quakes.

Understanding earth systems is a slow business. The notion of tectonic plates, after all, was first proposed in 1915 and took until the 1960s to be accepted. Making the links between climate change, earthquakes and volcanic activity is happening now, for good science requires good evidence, no matter how intuitively appealing the logic might be. Now, Eyjafjallajökull is providing some of that evidence.

Rahul Goswami is a developmentpolicy analyst who lives in Berlin, Germany, and Goa, India. He can be  contacted  at: makanaka@pobox.com

 
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