Thursday, October 23, 2014

Global Warming Might Spur Earthquakes and Volcanoes

I thought about this when the volcano in Iceland erupted, since I have posted on this subject in the past, but didn't have time to post about it at the time of the eruption. I have wondered if others have noticed the possible link between the melting of the Iceland ice sheets and the eruption of the volcano, and I see that they have.


Global Warming Might Spur Earthquakes and Volcanoes
Andrea Thompson | August 30, 2007

Earthquakes, volcanic eruptions, tsunamis and landslides are some of the additional catastrophes that climate change and its rising sea levels and melting glaciers could bring, a geologist says.

The impact of human-induced global warming on Earth's ice and oceans is already noticeable: Greenland's glaciers are melting at an increasing rate, and sea level rose by a little more than half a foot (0.17 meters) globally in the 20th century, according to the Intergovernmental Panel on Climate Change.

With these trends in ice cover and sea level only expected to continue and likely worsen if atmospheric carbon dioxide levels continue to rise, they could alter the stresses and forces fighting for balance in the ground under our feet—changes that are well-documented in studies of past climate change, but which are just beginning to be studied as possible consequences of the current state of global warming.

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One particular feature that can change the balance of forces in Earth's crust is ice, in the form of glaciers and ice sheets that cover much of the area around Earth's poles plus mountains at all latitudes. The weight of ice depresses the crust on which it sits.

As the ice melts, the crust below no longer has anything sitting on top of it, and so can rebound fairly rapidly (by geological standards). (This rebounding is actually occurring now as a result of the end of the last Ice Age: The retreat of massive ice sheets from the northern United States and Canada has allowed the crust in these areas to bounce back.)

Areas of rebounding crust could change the stresses acting on earthquake faults and volcanoes in the crust.

"In places like Iceland, for example, where you have the Eyjafjallajökull ice sheet, which wouldn't survive [global warming], and you've got lots of volcanoes under that, the unloading effect can trigger eruptions," McGuire said.

With the changing dynamics in the crust, faults could also be destabilized, which could bring a whole host of other problems.

"It's not just the volcanoes. Obviously if you load and unload active faults, then you're liable to trigger earthquakes," McGuire told LiveScience, noting that there is ample evidence for this association in past climate change events.

"At the end of the last Ice Age, there was a great increase in seismicity along the margins of the ice sheets in Scandinavia and places like this, and that triggered these huge submarine landsides which generated tsunamis," McGuire said. "So you've got the whole range of geological hazards there that can result from if we see this big catastrophic melting."

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http://e360.yale.edu/feature/could_a_changing_climate_set_off_volcanoes_and_quakes/2525/

Fred Pearce
May 7, 2014

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British geologist Bill McGuire, in a troubling new book, Waking The Giant: How a Changing Climate Triggers Earthquakes, Tsunamis and Volcanoes.

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The most solid evidence for climatic influence on geology comes from the end of the last ice age, around 12,000 years ago, says McGuire, who is a volcanologist and professor of geophysical and climate hazards at University College London. Analysis of volcanic deposits, published in the past decade by several authors, has found that this period of rapid climate change, when ice sheets retreated from much of the planet, coincided with a sudden outburst of geological activity. The incidence of volcanic eruptions in Iceland increased around 50-fold for about 1,500 years, before settling back to previous levels.

What happened? McGuire makes the case that during the long preceding glaciation, the weight of ice some two kilometers thick over Iceland maintained high pressures underground that kept magma at the root of volcanoes solid and suppressed eruptions. But as the ice melted, the huge

weight was released and the land surface lifted, sometimes by hundreds of meters. This reduced the pressure below. He cites Freysteinn Sigmundsson at the Nordic Volcanological Center at the University of Iceland in Reykjavik, who says: “Reduction of pressure enabled mantle rocks to melt, creating a zone of magma upwelling underneath Iceland.” Magma production increased 30-fold – that magma, the argument goes, burst out in a spectacular epidemic of volcanic eruptions.

Similar, though less pronounced, surges in volcanic activity occurred at that time across much of the planet, wherever large ice sheets or small tropical glaciers melted, says Hugh Tuffen, a volcanologist at the University of Lancaster in England. From the Eifel mountains of Germany to the Chilean Andes, and from California to Kamchatka, volcanoes were awakened, says McGuire, who chaired a conference on climate change and geology at the Royal Society in London in 2009.

While the planet’s volcanoes have been relatively peaceful during the long stable climate since then, McGuire warns that we need to watch out as the world starts to warm once more. “Volcanoes can be incredibly sensitive to tiny changes to their external environment, constantly teetering on the edge of stability,” he says.

Defrosting the planet’s cold regions has for some years been implicated in a range of “natural” disasters. The rapid melting of glaciers creates dangerous lakes of meltwater, perched high in the valleys of the Himalayas and Andes.

Thawed soil unleashes landslides. Christian Huggel, a geographer at the University of Zurich, Switzerland, found in a study of mountain slope failures in Alaska, New Zealand and the European Alps that “all the failures were preceded by unusually warm periods,” lasting days or weeks. There are also concerns that warming will release the potent greenhouse gas methane from permafrost and continental shelves, creating a dangerous feedback to global warming itself.

But McGuire is talking about changes deep in the Earth’s crust, caused by the lifting or imposing of the weight of ice and ocean water at the surface. And the concern relates to earthquakes as well as volcanoes. For earthquakes, the evidence points to changes in sea levels, as well as the melting of ice.

Many geological fault lines are on a knife-edge, awaiting any nudge to send their seismic mayhem to the surface, says McGuire. His University College London colleague Serge Guillas has found that, over the past 40 years, El Nino cycles in the tropical Pacific Ocean have triggered a regular seismic response as the pressure of water has changed with short-term sea level fluctuations. There are more earthquakes in the eastern Pacific in the months after the cycle lowers sea levels in the area by a few centimeters, which flexes the plates beneath.

A 2009 study co-authored by Selwyn Sacks, a geophysicist at the Carnegie Institution in Washington D.C., concluded that something as seemingly insignificant as low atmospheric pressure in the heart of typhoons was sufficient to trigger slow earthquakes in strata east of Taiwan.

The evidence from volcanoes of short-term influences is even more startling. According to Oxford University geologists Ben Mason and David Pyle the planet has volcanic seasons. In the Northern Hemisphere, eruptions happen most frequently between November and April. The reason, they say, is shifts in water round the globe. This movement of water slightly squashes or releasing the land beneath, at times pushing magma to the surface rather like toothpaste in a tube.

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McGuire is keen to underline that his message “is not intended as a speculative rant.” He is simply reviewing the voluminous literature already in the public and peer-reviewed domains. He makes a point of dismissing talk that climate change might have caused the Sumatra earthquake that triggered devastating Indian Ocean tsunami in 2004 as “clearly nonsense.” But he insists that “people who find the idea [of climate change triggering geological events] flaky don't appreciate that the link between abrupt climate change and a response from the solid Earth is supported by huge amounts of research.”

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One place we might expect trouble is Iceland, the scene of the eruption of Eyjafjallaj√∂kull two years ago. Its smoke billowing across flight paths grounded transatlantic flights for a week. Nobody is blaming that eruption on climate change, but the island’s ice cap has been thinning for more than a century now. In response, the land surface is rising, often by more than 20 millimeters a year. This is still an order of magnitude less than the rates at the end of the last ice age, but Sigmundsson says it nonetheless creates “highly significant” pressure release — and new magma ready for ejection.

There are other dormant volcanoes and quiescent fault-lines lurking beneath the thick ice caps over Greenland and Antarctica. Andrea Hampel, a geologist at Leibniz University in Hanover, Germany, warns that the subdued geology in both places today is likely caused by the presence of large ice sheets. “Shrinkage [of the ice] owing to global warming may ultimately lead to an increase in earthquake frequency in these regions,” she predicted in a paper published two years ago. “This effect may be important even on timescales of 10 to 100 years.”

Tuffen, of the University of Lancaster, agrees. He points out that the West Antarctic Ice Sheet is set to thin by 150 meters by 2100, potentially waking dormant volcanoes. Other volcanoes in the firing line, he says, could include Nevado del Ruiz in Colombia and Cotopaxi near Quito, the capital of Ecuador.

We could already be seeing a resurgence of earthquakes. McGuire admits there is no certainty about any link, but he points out that there has been “an unprecedented cluster of massive earthquakes” in recent years. Since 1900, the world has been struck by seven “super-quakes,” with a magnitude exceeding 8.8. While only one of them occurred in the first half of the 20th century, three more came in the second half, and there have been three more in the past seven years, bringing death and destruction to Sumatra, Chile, and Japan.

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McGuire concludes that climate scientists at the IPCC have blind spots, both about geology and about learning the history of what happened during past eras of climate change. The science of geological responses at the end of the last glaciation, he says, “is extremely well established.” Nonetheless, the implications for the future remain largely ignored even among the most strident campaigners for action on climate change.

Nobody should want climate scientists to rush around the world warning of geological Armageddon. Too much remains unknown. Caution certainly is justified. But the danger is that a topic of potentially huge importance ends up being ignored. And the research needed to substantiate — or to repudiate — these concerns is never done. That would be unwise.

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