IPCC Studies Link Between Warming and Earthquake Activity
Climatequake: Will global warming rock the planet?
The New Scientist, Oct. 5, 2011
The Earth's crust will heave as ice melts and the sea rises – and that could unleash earthquakes, volcanoes and tsunamis.
Few things are more likely to prompt instant ridicule from climate sceptics than the idea that there might be a link between global warming and geological disasters such as earthquakes, volcanic eruptions and tsunamis. "Earthquakes are caused by tectonic plate movements - they are not caused by Bubba driving his SUV down the highway," is typical of the responses found in the denialist blogosphere.
Yes, the Earth moves all by itself, but it is becoming increasingly clear that climate plays a role in when and how often. What happens on the surface can suppress quakes and eruptions - and trigger them. There are already signs of such effects in the world's northern regions, which are warming fastest.
So seriously is the issue being taken that an upcoming special report on extreme events and disasters related to climate change, commissioned by the Intergovernmental Panel on Climate Change, will include a section on it. So what exactly is going on and what can we expect during the next century and beyond?
The idea that climate change can affect events such as earthquakes is not as outlandish as it might first seem. While the power of earthquakes comes from the movements of tectonic plates deep beneath the surface, even these stupendously massive structures can be influenced by what is happening at the surface. The rapid erosion of huge quantities of material by the monsoon rains in India, for instance, has affected the motion of the Indian platee over the past few million years.
On a more immediate timescale, there is already plenty of evidence that human activity can trigger earthquakes. The building of vast dams has often been linked to seismic activity, for instance. Some blame the Great Quake of Sichuan in 2008, which killed 80,000 people, on the recently constructed Zipingpu dam just 5 kilometres away from the epicentre.
Mining and drilling activities can also trigger small earthquakes, and at least one geothermal project has been cancelled because of fears of further quakes. And if small geothermal projects can trigger quakes, it is not so surprising that altering the climate of the entire planet will have an effect too.
The crux of the problem is simple: anything that increases or decreases the load on the Earth's crust causes stresses and strains. When this happens slap bang on top of one of the world's many volcanoes or geological faults, where the crust is already under strain, it can make the area more or less likely to erupt or slip. And there is a very heavy substance whose movements depend largely on the weather and the climate: water.
During past ice ages, vast ice sheets several kilometres thick built up over northern Eurasia and north America. The weight of the ice pinned down faults and suppressed the flow of magma. When the ice melted, there was a flurry of earthquakes and volcanic eruptions as faults began to move again.
These ice sheets were so massive that sea level rose by 120 metres after they melted. However, even far smaller changes in the distribution of water are enough to trigger earthquakes and volcanic eruptions. A recent study of earthquakes on the Easter microplate in the Pacific, for example, found that a dip in local sea levels of only 20 centimetres due to changes in trade winds before an El Niño event raised the average number of monthly earthquakes from two to eight. When El Niño arrived, raising the local sea level by 50 centimetres, fewer earthquakes occurred.
And Mount Pavlof, an active volcano on the Alaska peninsula, erupts more often in the winter. This may be a result of sea levels rising by 30 centimetres in the winter due to local storms, says Steve McNutt of the Alaska Volcano Observatory in Fairbanks. This would squeeze magma upwards as the weight of the water on the seabed either side of the peninsula increases.
While these two examples are seasonal and linked to the weather, in Alaska there are signs of climate-driven changes. "I think of Alaska as the 'canary in the cage' because it is very tectonically active, there are a lot of active faults, a lot of volcanoes and it's very high latitude and that is where the temperatures are rising most rapidly," says Bill McGuire, a volcanologist who heads the Benfield Hazard Centre at University College London.
In the south of Alaska, large glaciers sit over a major fault where the Pacific-Yukatat plate dips under the continent. During the past century, the glaciers that have pinned down and stabilised the fault have thinned by hundreds of metres, and the crust beneath has rebounded by up to 20 millimetres per year.
Ice loss was particularly fast during a warm spell between 2002 and 2006. The frequency of small earthquakes in the area increased during this time, according to Jeanne Sauber of NASA's Goddard Space Center in Maryland and Natalia Ruppert of the University of Alaska, Fairbanks. Sauber and Ruppert also think that the magnitude 7.2 St Elias earthquake in this region in 1979 occurred earlier than it might otherwise have done, due to the loss of ice (Geophysical Monograph Series, vol 179, p 369). The quake was in a unpopulated area and no one died.
Even if climate change is indeed to blame these are relatively minor events. On a global level, there has been no significant increase in either volcanic eruptions or earthquakes as a result of the warming over the past century. Certainly, no researcher is claiming there is any connection between climate change and major disasters such as the Japanese megaquake earlier this year.
There is, however, evidence that warming has triggered major landslides And there has been very little warming so far compared with what is to come: McGuire thinks we will we see a clear effect on volcanoes and earthquakes when climate change really gets going. "Earthquakes and volcanic eruptions over a hundred years would cluster. You need a certain amount of strain to accumulate and climate change may bring forward the time that takes," he suggests. This will mean more earthquakes and eruptions in a given period, rather than more in total, he says.
The main reason is melting ice. There is far less ice now, of course, than at the end of the last ice age. But the planet is warming much faster, so sea level may rise as fast as it ever did before. While sea level rose just 0.17 metres over the 20th century, most glaciologists expect sea level to rise around a metre by the end of the 21st century. This would add an extra tonne per cubic metre to undersea and coastal faults.
The good news is that it will probably weigh down and stabilise faults beneath the sea floor. The bad news is that it will create extra stress at the coast. Here there will be a kind of see-saw effect as the seabed is pushed down. That could add enough stress to trigger a quake on faults that straddle the coast, or run parallel to them, such as the San Andreas fault in California, the North Anatolian fault in northern Turkey, and the Alpine fault in New Zealand.
The next hundred years of sea-level rise is only likely to trigger an earthquake on a fault system that is already very close to failure, says Karen Luttrell of the US Geological Survey in Menlo, California. Still, that could mean people suffering an earthquake that otherwise would not have happened in their lifetime.
Apart from this coastal effect, the areas most likely to be affected are sparsely populated and are already hotspots for geological activity, such as Iceland. Its largest icecap, Vatnajökyll (pictured left), sits on top of two active volcanoes. The icecap has lost 10 per cent of its mass since 1890, which is having two effects. The crust is rebounding, potentially bringing the magma chambers beneath closer to collapsing and triggering earthquakes. It also causes more magma to be produced at depth, as lower pressure can lead to rocks melting. This second effect is peculiar to Iceland, where hot magma is already close to the surface because it lies along the mid-Atlantic ridge.
Carolina Pagli of the University of Leeds, UK, and Freysteinn Sigmundsson of the University of Iceland in Reykjavik recently calculated that the thinning of the icecap is increasing magma production each year by 10 per cent. To put it in perspective, the extra 1.4 cubic kilometres produced in each century is similar to the 2 cubic km per century already produced under the Bardabunda volcano. So almost a volcano's worth of extra magma is being produced due entirely to the melting of the ice.
Adding more magma to an existing chamber is likely to mean more frequent eruptions as the chamber fills and empties more quickly. "It is likely to cause an increase but it is not possible to tell when," Pagli is quick to point out. "We don't know how quickly the magma that is being produced moves to the surface," she says.
While Iceland is a special case, in that it sits over a major spreading ridge, Pagli points out that wherever ice caps or glaciers above volcanoes melt, they will cause the crust above the magma chambers to flex, which might make them more likely to fail. "Volcanoes in Antarctica may be subject to this," she suggests. There are also chains of volcanoes covered by large glaciers in the Aleutian Islands in Alaska and parts of Patagonia.
In Greenland and Antarctica, extensive melting of the ice caps could even rewaken long-dormant faults. This would result in earthquakes that would not have occurred otherwise, and some of them could be major ones. Both polar regions are seismically quiet at the moment, but according to Andrea Hampel, a geologist at Hannover University in Germany, that is probably because of the vast amount of ice that is weighing them down. While few people live near these areas, coastal earthquakes in remote places could still cause major disasters by triggering tsunamis that speed across oceans and hit densely populated areas. Around 8000 years ago, after the end of the last ice age, there was a massive underwater landslide, called the Storegga slide, off the coast of Norway. An estimated 3200 cubic km of seabed slid down the edge of the continental shelf, generating a huge tsunami with waves up to 25 metres high, which engulfed parts of Scotland, Norway and Iceland.
The slide is thought to have been triggered by earthquakes, which in turn were caused by the rebounding of the crust in northern Europe after the ice melted. Studies of the sea floor show that the Storegga slide was one of a series of megaslides in this area over the past 500,000 years, most of which occurred in the aftermath of ice ages.
Underwater slides could occur off many coastlines around the world. A 1998 tsunami that killed 2000 people in Papua New Guinea, for instance, was caused by an undersea slide triggered by an earthquake. So if rising sea level triggers more earthquakes in coastal areas, in theory, it will also increase the odds of underwater slides and thus of tsunamis.
Overall, then, the evidence does point to a small but real increase in the likelihood of earthquakes, volcanic eruptions, landslides and tsunamis over the next century or so as a result of climate change. The effect is likely to be greatest in areas where few people live, minimising the threat to lives. Even those who live far from any volcanoes or quake zones, however, could feel the economic and practical consequences.
The eruption of the Eyjafjallajökull volcano in Iceland in April 2010 grounded flights across Europe for nearly a week, while an eruption at Chile's Puyehue-Cordon Caulle volcano in June this year had a similar effect across the Pacific in southern Australia. Neither eruption had anything to do with climate change, but it is the type of problem that we - or our children - are likely to see more of if McGuire's predictions about more frequent eruptions are borne out.
In a world that is going to suffer from ever more catastrophic floods and storms, killer heatwaves and devastating droughts, the risk of a few more earthquakes and volcanic eruptions, mostly in remote areas, might seem to be a relatively minor issue. That may well be true, but it is yet another item to add to the already long list of adverse consequences predicted or beginning to occur as a result of climate change. Events such as earthquakes also strike with little if any warning, so they can kill far more people than, say, hurricanes and floods.
What's more, geological events such as earthquakes, volcanoes and tsunamis have always been seen as completely beyond our control. Now it appears this is no longer entirely true - we have the power to prevent at least a few of them if we choose to.