Mt Aso could erupt much sooner, scientists warn

New surface ruptures and faults alter properties of Aso volcano

Damage from the 2016 Kumamoto earthquake could hasten Mt Aso's eruption, volcanologists warn. In a paper published in Science , Kyoto University researchers and colleagues report on new faults in the vicinity of Mt Aso's magma chamber and volcanic cones, which they say could alter spatial and mechanical properties of the Aso volcano.

Mt Aso is one of the largest active volcanoes in the world. The 16 April 2016 Kumamoto earthquake, study authors say, was a rare opportunity to study how faults form in the vicinity of volcanoes. "Our survey group went to the epicenter area one day after the event and continued field work for the past half year after the earthquake," says Aiming Lin of Kyoto University, who led the study.

The Kumamoto earthquake enabled the researchers to do a before-and-after comparison of fault distribution in the area. Field investigations, seismic data, and analysis of high-resolution Google earth images show that the earthquake produced new faults and surface ruptures.

Some of these cut the Aso caldera but terminated there.

"Magma is fluid so it absorbs stress. That's why the damage -- the surface ruptures -- shouldn't travel any futher," says Lin. "Large earthquakes often accompany or precede volcanic eruptions. The presence of magma does have an association with the distribution of active faults. But whether volcanoes affect the formation of new faults following an earthquake has remained unclear due to a lack of case studies.

"Our findings show that propagation of ruptures from this earthquake terminated in Aso caldera because of the presence of magma beneath the Aso volcanic cluster."

The newly formed co-seismic ruptures under Aso caldera are potential new channels for magma venting, thus changing the physical dynamics of Aso volcano, such as where pressure is concentrated. These then influence factors like the nucleation of interpolate earthquakes, seismicity patterns, source rupture processes, strong ground motion and recurrence behavior of fault segments. The study results, the authors write, could play an important role in reassessing volcanic hazard around Aso.

And Mt Aso actually did erupt 8 October 2016, after the research team had submitted the paper.

"We were amazed that Aso erupted after 36 years of dormancy, as we had just documented in this paper how the new faults changed the spatial and mechanical dynamics of the volcano," says Lin.