Proof our planet is cracking under stress

 

Melting ice is stressing our planet. Sea levels are shifting. Volcanoes and fault lines are stirring. The Earth's axis is tipping.

We could be in for a rough ride ahead.

"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. Not only has this happened several times throughout Earth's history, the evidence suggests that it is starting to happen again," Professor Bill McGuire warned back in 2006.

He's not talking about the weather. He's talking about climate - the way weather averages out.

With overall temperatures rapidly warming, polar ice sheets are shrinking. Glaciers are melting. Soil moisture is evaporating.

That means a lot of weight is suddenly shifting about our planet's surface.

In turn, this is causing the Earth's crust to undergo rapid change.

"There is a growing consensus that if climate change continues unchecked, we can expect not only a warmer future, but a more geologically turbulent one too," McGuire wrote.

Now, with more than a decade worth of new research, that consensus continues to grow.

CAUSE AND EFFECT

There is no statistical evidence of an increase - or decrease - in the rate of significant volcanic eruptions in the past 600 years.

This is despite a dramatic spike in the number of such events being reported.

The Global Volcanism Program says sprawling populations, improved technology and better communications means more eruptions are being seen and recorded.

Farms, settlements, towns and suburbs are appearing on volcanic slopes.

New Zealand's city of Auckland, for example, is built among 48 different volcanic cones. It's an area that has experienced 55 eruptions in the past 190,000 years. Volcanologists say they can't predict when the next one will hit.

And, as the White Island tragedy highlights, volcanoes invoke a deadly allure.

In New Zealand alone, volcanoes such as Rangitoto, Tongariro, Ngauruhoe, Ruapehu, Taranaki, and the South Island's Banks Peninsula have become focal points of a thriving tourism industry.

So understanding the processes driving eruptions has become a pressing matter.

But those processes appear to be changing under our feet.

WEATHER VERSUS CLIMATE

"There are lots of myths about earthquakes," says NASA's Alan Buis. "A common one is that there's such a thing as 'earthquake weather'."

The idea that a few hot days warns of impending seismic activity is an ancient one. But it won't go away.

He places the blame at the feet of ancient Greek philosopher Aristotle who speculated earthquakes were the result of winds breaking out of subterranean caves.

"He believed the large amounts of air trapped underground would make weather on Earth's surface before a quake hot and calm," Buis says.

Humanity's collective knowledge has advanced considerably in the 2300 years since then.

We now know that most earthquakes and volcanoes are the result of immense forces within the Earth. These produce ruptures along complex fault-lines in underground rock.

And then there are the deep conveyor-belt like tectonic plates that make up our planet's crust.

"Finally, we know the statistical distribution of earthquakes is approximately equal across all types of weather conditions," Buis adds. "Myth busted."

But, there is a 'but'.

IT NEVER RAINS …

The US Geological Survey has discovered there is one link between weather and earthquake.

Major storms, such as cyclones and hurricanes, can produce substantial changes in atmospheric pressure. This sometimes triggers a 'slow earthquake' - a slow but steady movement that does not create any noticeable jolt.

"They note that while such large low-pressure changes could potentially be a contributor to triggering a damaging earthquake, the numbers are small and are not statistically significant," Buis says.

And then there's the fact that weather is not the same as climate.

Recent NASA research in California, Oregon and Washington indicate extended drought could have implications of seismic proportions.

Between 2011 and 2017, the Sierra Nevada mountain range lifted by up to 2.5cm as it shed water and lost weight. Then it fell more than 1cm after heavy rains.

"Such stress changes could potentially be felt on faults in or near the range," Buis writes.

It supports earlier research linking depleted subterranean groundwater aquifers to seismic activity on the San Andreas Fault. Once again, the change in pressure and weight had a domino effect.

"Even though such changes might be small compared with stress changes caused by the normal build-up of stress on a fault from tectonic processes, it could potentially hasten the onset of the next big quake," says NASA geophysicist Paul Lundgren.

But there are still too many unknown variables at play to be sure.

"We're not close to being able to predict when an earthquake may occur as a result of climate processes," he concludes. "Even if we know that some outside climate process is potentially affecting a fault system, since we don't know the fault's potential state of readiness to break, we can't yet make that extra inference to say, 'ah-ha, I might get a quake a week or a month later'."

But there's another 'but'.

 

WEIGHTY MATTERS

One square metre of water weighs one tonne. A square metre of ice is about 900kg.

Glaciers can weigh in the billions of tonnes.

Researchers already know dramatic changes in the water levels of lakes and dams can trigger local seismic activity.

But upscaling this impact to a global level is difficult.

We know glaciers are retreating rapidly around the world.

So, what if such enormous weights shift?

"With this in mind, 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 and even landslides," Professor McGuire says.

The magma beneath the Earth's crust is shifting.

Recent studies show Alaska is rising some 3cm every year. As the remaining coastal glaciers disappear, lowland areas are growing - draining estuaries and lakes.

"There is a much more rapid rate of ice loss here compared to many regions of the world," University of Alaska professor Eran Hood says. "The human fingerprint of global warming is just exacerbating issues and increasing the rate of glacial isostatic adjustment."

Sea levels are rising in places like New York. But, in Alaska, sea levels are falling.

Researchers believe this is the result of shifting loads on the Earth's crust.

It's nothing new. What is new, however, is the cause.

Some 19,000 years ago, the Earth buckled under the weight of enormous ice sheets. This was the Last Glacial Maximum. Ice 1km thick depressed the ground beneath some 250m. Magma was squeezed outward, forcing upward any land unburdened by ice.

When the ice receded, the magma was drawn back into the freshly unburdened Earth.

This all took place on an enormous scale.

What geophysicists are trying to work out is how this translates to our current circumstances.

Many of the earthquakes we feel today are part of an 11,000-year-old rebound from the last Ice Age. But, with the Arctic and Antarctic circles losing immense weight unnaturally fast, we may experience this fallout much faster.

UNLOCKING THE GATES TO HELL

Glaciers are melting in the Alps, the Himalayas, the Rockies and the Andes.

All sit astride significant fault lines.

What impact this will have remains unknown.

But the uplifting of the ocean floor around melting Greenland is cause for particular concern.

Researchers fear the shift in weight could trigger earthquakes strong enough to dislodge mountains of coastal sediment.

This would cause enormous tsunamis.

A similar sediment collapse 8000 years ago off the coast of Norway saw a 20m wave swamp the Shetland Islands, and a 6m wave strike Scotland.

Massive glaciers suppress earthquake activity. And, in the case of Norway, research shows its volcanoes have been quietest when the surrounding glaciers were thickest.

But take those glaciers away, and the volcanoes wake.

In the past five years, Iceland has experienced three significant eruptions. That's an unusually high number for the area.

In Alaska, where the Pacific Plate slides under the North American Plate, the retreat of glaciers may also be unclamping the fault-line's brakes.

"The burden of the glaciers was keeping smaller earthquakes from releasing tectonic stress," NASA geophysicist Erik Ivins says.

SHAPING THE FUTURE

Shifts in the Earth's crust are being seen far from existing tectonic rifts and known fault lines. A 2008 study warns melting glaciers may be reawakening long-dormant sites.

New Madrid in the Midwestern US has experienced new earthquakes in areas long thought dead. Molten rock once attempted to force its way upward here, only to be held back by ice sheets.

That barrier has long since been removed. And the restless Earth is causing the ancient vents to open once again.

The Earth's wandering North Pole is a sign that magma flows are shifting.

The concentrations of iron that help fuel our planet's magnetic field have changed course.

Up until 2000, the North Pole was steadily moving towards Canada.

Since then it's done an abrupt about-face, racing towards Europe at up to 50km a year.

As the magma redistributes itself to find a new equilibrium, it's changing the shape of our planet.

And causing our days to lengthen.

So far, only the most sensitive instruments have seen this. But it's a natural consequence of ice turning into water.

"Because glaciers are at high latitudes, when they melt, they redistribute water … towards lower latitudes, and like a figure skater who moves his or her arms away from their body, this acts to slow the rotation rate of the Earth," Harvard University geophysicist Jerry Mitrovica said of a 2015 study.

"Imagine a figure skater who doesn't stick their arms straight out but rather sticks one at one angle and the other out at another angle. The figure skater will begin to wobble back and forth."

Jamie Seidel is a freelance writer. Continue the conversation @JamieSeidel



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