Mega-quakes can cause volcanoes to sink

Massive earthquakes can cause far-off volcanoes to sink by as much as 15 centimetres, according to new research.
The magnitude-9.0 earthquake that struck Japan in 2011 caused volcanoes as far as 200 km from the epicentre to sink up to 15 centimetres, researchers found.
A separate team of scientists observed similar effects in five volcanic regions of Chile after the magnitude-8.8 quake that struck the country in 2010.
This is the first time scientists have seen a string of volcanoes drop after an earthquake.
The two teams have different explanations for why the volcanoes sank, according to the studies, published in the journal Nature Geoscience.

However, both groups agree it is likely scientists will discover more examples of drooping volcanoes after big earthquakes, and find a single mechanism that controls the process, 'LiveScience' reported.

"It's amazing, the parallels between them. I think it makes a really strong case that this is a ubiquitous process," said Matthew Pritchard, a geophysicist at Cornell University in Ithaca, and lead author of one of the studies.
Previous research has noticed that volcanoes sometimes blow their top after earthquakes. And colossal earthquakes, such as the 2011 Japan earthquake and the 2010 Chile quake can trigger small tremors at volcanoes thousands of kilometres away.

After the Chile and Japan quakes, the research teams behind the two new studies worked independently to track signs of coming eruptions.
However, instead of finding bulging volcanoes - a hint that magma is rising underground - the teams only discovered sagging mountains, or no changes at all. No signs of eruptions appeared in the scores of volcanoes in the two countries.
Instead, volcanoes and massive caldera complexes dropped by 2 to 6 inches. Each area was shaped like a long oval, lined up parallel to the offshore earthquake fault that was located between 200 to 300 km away. Satellite data revealed the changes to both teams.

"Even without visible eruptions, large earthquakes affect volcanoes," Youichiro Takada, a geophysicist at Kyoto University in Japan and lead author of one of the studies, told the website.
Pritchard and his colleagues, who studied the Chilean earthquake, think the seismic shaking uncorked fissures and fractures that released pent-up hydrothermal fluids at the volcanoes, akin to shaking a soda bottle and then opening the top. As the fluids escaped, the ground settled and sank.
However, Takada's group, who studied the Japan quake, thinks magma chambers under the volcanoes sank more than the surrounding region. The hot rock is weaker and deforms more in response to the crustal changes caused by the massive quake.