Friday, 29 April 2016

How climate change triggers earthquakes


Image by Nirmal Dulal and courtesy of Wikimedia Commons.

24 April, 2016

One year ago, Nepal was rocked by a devastating 7.8-magnitude earthquake. In conjunction with a major aftershock one month later, the April 25 disaster claimed around 9,000 lives, injured tens of thousands more, and reduced holy sites like the Dharahara tower and Vatsala Durga to rubble.

The quake was not entirely unexpected. Residents in this seismically active part of the world have collected records of seismic activity for hundreds if not thousands of years. Earlier earthquakes have done far more damage. An 8.1-magnitude quake in 1934, for example, resulted in the deaths of 19,000 in Nepal and neighboring India.

But as world leaders lined up at the United Nations on Friday to commit their nations to greenhouse gas reductions intended to interrupt the worst manifestations of warming-driven climate change, earthquakes were likely not on the top of anyone’s mind. Global warming means deepened droughts and strengthened storms, the loss of sea ice and glaciers, and speeding up of sea-level rise. Some reporting moves the goalposts into social impacts of such a warmed world to project social crises such as war and famine. But one area is often overlooked: earthquakes.

The reticence of today’s policy makers and climate communicators to roll more frequent or strengthened earthquakes into the forecast is understandable—especially when there is no “hockey stick” to hold up linking earthquake activity to the thickening greenhouse layer, as can be done with heat, with sea-levels, with disasters broadly. There was that tripling of the “great” earthquakes over the 00’s threshold, but suggestions of a climate link were batted away at least in one case for a lack of proper academic citations.

Those living on the front lines of climate change, however, aren’t so guarded.

There seems a direct relationship between glacier retreat and earthquakes,” said Pakistani researcher and writer Hamid A. Mir. “The local communities of this area have developed a common belief that the greater are the floods in summer spell the greater and more frequent will be earthquakes during winter spell. This is what we have been experiencing for the last three decades, ever since climate change has taken momentum in the area.”

In fact, the the research community has long studied the relationship between changes in surface water weight with seismic activity below.

The rapid expansion of large-scale hydropower projects worldwide inspired Indian seismologist H.K. Gupta’s to write “Dams and Earthquakes” in 1976. The controversy it caused at the time dissipated by the time he updated the work in 1992, by then listing 70 known cases of reservoir-induced earthquakes, including tremblers in China, Zambia, Greece, India, and the United States, among others.

The question today is what impact our fast disappearing glaciers will have on the tectonic plates they’re floating upon.

In a 2004 paper, researchers reported that melting glaciers in Southern Alaska was to blame for 1979’s 7.2-magnitude St. Elias earthquake. A similar study four years later found that increased “ice wastage” between 2002 and 2006 resulted in a corresponding increase of tectonic activity in Icy Bay, Alaska.

So what of the climate-driven retreat of glaciers worldwide? What are we to expect?

In Ecuador, where a 7.8-magnitude quake took the lives of hundreds earlier this month, glaciers are melting fast, with nearly half of the Cotopaxi glacial cap having melted off just since 1976.

Screen Shot 2016-04-24 at 8.45.40 PM“The main lesson we should take from the post-glacial period and from our recent dam-building campaigns is that the removal or addition of ice and water—in sufficiently large quantities—can have a significant impact on the behavior of underlying and adjacent faults,” Bill McGuire writes in his 2012 book, “Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis, and Volcanoes.”

Even “minor” shifts in weight in this vulnerable area (which McGuire, professor emeritus of Geophysical and Climate Hazards at University College London, likens to a mere geologic “handshake”) threaten a seismic response. With the onset of global warming, shifting gigatonnes of water flowing from the Himalaya threaten “waking the giant” of tectonic misbehavior.

Across the high Himalaya and broader Third Pole region, temperatures are rising several times faster than the global average, resulting in the accelerating appearance of glacial lakes where previously there was only ice and snow. Chinese researchers recently conducted what is thought to be the first glacial inventory using Landsat imagery and reported last year that between 1990 and 2010 glacier melt created 1,100 new high-altitude lakes across the Himalaya, Tibetan Plateau, Hindu Kush, and Pamir Mountains. During that 20-year period, the number of identified lakes grew from 4,602 to 5,701.

Global risk analytics firm Verisk Maplecroft ranks Nepal as one most climate vulnerable nations on earth. Increasingly erratic rainfall patterns and rising temperatures from global warming are likely to damage the agriculture and forestry sectors of Nepal’s economy now employing an estimated three-quarters of all Nepalis, for example.

Even more damaging, however, may be the threat of massive flooding driven by already increasing glacier melt, extreme rainfall events, earthquakes, and the formation and expansion of glacial lakes, all funneling into a rising risk of Glacial Lake Outburst Floods (GLOFs). In a 2010 review of the growing global glacial retreat, Colombia University’s Ben Orlove recounts a 1985 outburst flood in Nepal that released a “wall of water” 10 meters high that traveled nearly 100 kilometers and destroyed 14 bridges and a “nearly completed” hydroelectric plant.

Both the total reliance on hydropower and the rapidly melting landscape pose additional threats via earthquake, which are capable of getting much worse.

Geologic features deep in the Himalayas once considered outside the range of quake behavior may be much more conducive than previously thought. A pair of researchers last year found that quake ruptures “extended past a ‘lock line’ where brittle rock becomes more plastic in its behavior—a region where slip was expected to creep along quietly and not contribute to the overall power of the earthquake.”

In writing up their finding, researchers Eric Hand and Priyanka Pulla, warned of a coming “megaquake.”

The discovery suggests that, as awful as the present disaster is, future earthquakes in the Himalayas could end up being mightier and more calamitous than modelers assumed,” the pair wrote.

Even under the growing threat of GLOFs and earthquakes, the broader region’s energy needs have spurred a massive water grab that threatens to make the Himalayas the “most dammed region in the world.” This brings a risk of dam failure delivering tsunami-like floods. “It would be a Fukushima moment—earthquake followed by tsunami,” Buckley writes in The Ecologist. “Only in this case, an inland tsunami would be unleashed on a river. The megadam becomes a lethal hydro-bomb, piling horror upon horror.”

Currently, India is involved in nearly 300 major dam projects and China roughly 100 such efforts. Nepal is pursuing several large dam efforts, including the West Seti Project, expected to be the highest Concrete Faced Rock Filled dam in the world when complete and hold 1,500 million cubic meters of water.

This post is adapted from the paper, “Climate Change and Earthquakes: Mitigating Future ‘Natural’ Disasters in Nepal,” presented by the author at the 4th Annual Himalayan Studies Conference in Austin, Texas.

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