A Supervolcano Stopped An Earthquake Dead In Its Tracks In Japan This Year

The eruption of Aso earlier this month may have been related to a powerful April earthquake. Daisuke Uragami AP/PA Images

Volcanoes and earthquakes are some of the most destructive forces of nature, and many wonder when the next supervolcanic eruption or “big one” tremor will bring civilization to its knees. In stark contrast to this apocalyptic reputation, an absolutely bizarre new study has revealed that, on occasion, volcanoes may stop earthquakes dead in their tracks.

Writing in the journal Science, the team from Kyoto University describes the fairly titanic battle in Japan between the April 16, 2016, Kumamoto earthquake and the Mount Aso caldera, sometimes referred to as a “supervolcano.”

The quake was one of several in a series of closely-spaced shallow tremors that injured thousands of people and killed at least 49. Shaking part of the western isle of Kyushu, it appeared to be centered at a point roughly 30 kilometers (19 miles) away from the volcano.

Reaching a magnitude of 7.3, the destructive event was generated by a complex fault network slipping forwards at a relatively shallow depth of only 10 kilometers (6 miles).

Most quakes in the region are far deeper. They are primarily caused by the descending of the Philippine Sea plate, and any new cracks in the rock tend not to snake up to the surface. However, the Kumamoto tremor cracked open rock right beneath the feet of millions.

A batholithic map of the Aso caldera, with reds representing peaks and greens representing low-lying land. NASA

Using a combination of seismic before-and-after data and satellite imagery, the team realized the ruptures breached the Aso caldera and came to a sudden halt. It appears that a zone of magma rising up to greet the world halted the so-called “unzipping” of the earthquake by redirected the incoming stress and strain upwards, before absorbing the pressure.

Lead author Aiming Lin, a professor of geophysics at Kyoto University, told IFLScience that this event was the first such interaction of its kind that had ever been officially discovered. However, Lin said that this “may not actually be a rare case,” noting that similar events may have occurred in 1707 and 1930 in central and eastern Japan.

Regardless, this earthquake was already fairly severe as it is, but it appears that the Aso supervolcano may have saved the region from a far more destructive event. However, there is a darker side to the tale that cannot be ignored.

Volcanologists are acutely aware that when a magma source’s internal pressure exceeds that of the confining pressure exerted by the surrounding rock, the roof tends to collapse and the magma rushes upwards, sometimes catastrophically.

There are many things that can cause an overpressure event, including changes in the chemistry of the magma, or nearby, highly-energetic events. These can include nearby subterranean nuclear weapon detonations or, of course, sizeable earthquakes, both of which transfer additional stress to the magma.

Additionally, new fractures can provide paths for magma to effortlessly migrate up to the surface. Either could have happened in Kyushu this year and caused Aso to erupt – and this study thinks that perhaps it did.

“We downplayed this sense during the review process,” Lin said. However, the “Aso volcano erupted on October 8 after a 36-year-long dormant duration. This took place the very day our paper was accepted by Science.”

Although it was far from being a supervolcanic eruption, the huge ash column that rose from one of its many nested peaks was a perhaps not coincidental sign of what the near-future will be like if more shallow quakes take place.

There is a massive source of magma brewing beneath Aso’s 25-kilometer-long (16 miles) crater. One day, sooner or later, it will breach the surface – either by its own volition, or with the help of a few conspiring earthquakes.

An effervescent eruption at Sakurajima, a nearby stratovolcano that feeds off the same vast magma source. bikeriderlondon/Shutterstock

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