Mega-Quakes Make Volcanoes Sink Into The Earth [STUDY]

By iScienceTimes Staff on July 1, 2013 5:35 PM EDT

volcanos
Volcanoes can sink into the Earth following mega-quakes, two new studies from independent teams show. (Photo: Reuters)

Mega-quakes not only cause massive amounts of damage to houses, lives and economies when they strike, but they also sink volcanoes, new studies published in Nature Geoscience found.

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The discovery was made by two teams independently studying volcanoes in Japan and Chile. After mega-quakes in 2010 and 2011, volcanoes in the area of the earthquakes fell as much as six inches.

"The observations are so similar in both places," said Matthew Pritchard of Cornell University, the lead author of one of the papers. "It's just a spectacular observation."

In 2010, an 8.8-magnitude mega-quake hit Chile in 2010, killing about 600 people; one year later, Japan was torn apart by a 9.0-magnitude mega-quake which killed 16,000 people and led to $235 billion in damages, the costliest natural disaster in history.

After the mega-quakes, scientists expected volcanoes to erupt too, something that can occur after big quakes. So scientists studied volcanoes in Chile and Japan, looking for signs of life, such as magma bubbling.

But what actually happened was that volcanoes didn't erupt, but sank further into the ground, even volcanoes that were far away. One volcano in Japan, on the island of Honshu, sunk 9.3 inches, and was 120 miles away from the mega-quake's epicenter. And in Chile, similar sinking occurred in five volcanic regions up to 130 miles away.

How does one know that a volcano has sunk a few inches into the ground, you ask? Satellite imaging, of course.

"We use satellite Interferometric Synthetic Aperture Radar (InSAR) and night-time thermal infrared data to [analyze] subtle changes in ground deformation and thermal activity at volcanoes in the southern volcanic zone since 2010," the authors the Chile mega-quake study explain in the abstract. "We document unprecedented subsidence of up to [6 inches] in five volcanic areas within weeks of the earthquake, but no detectable thermal changes."

This is the first time scientists have noticed volcanoes sinking after an earthquake, but probably not the last.

"It's amazing, the parallels between them," Pritchard told LiveScience. "I think it makes a really strong case that this is a ubiquitous process."

So what causes volcanoes to sink following mega-quakes? The two papers published in Nature Geoscience have different theories.

The Chilean earthquake studies think that seismic movements from the mega-quake cause fissures in the volcanoes to release hydrothermal fluids, which is, according to Live Science, like shaking bottle of soda and then opening it up. When the fluids escaped, the ground below the volcanoes settled and the volcanoes sink down a few inches.

The group that studied the mega-quake in Japan theorizes that magma under the volcanoes sank more than the ground around them. Hot rock under volcanoes is weaker than normal rock, and it may deform more easily after a seismic event like a mega-quake.

Whatever caused each grouping of volcanoes to fall, they are probably caused by the same thing, one geophysicist told Live Science.

"The observations in Japan and Chile are so similar that I'm certain that they are caused by the same mechanism (and maybe more than one), instead of two different ones in the two different countries," said Sigurjon Jonsson, a geophysicist not involved in either study.

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