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What would happen if Mount Fuji erupted for the first time in 307 years?

Reuters/Toru Hanai
Japan’s sleeping giant.
Published This article is more than 2 years old.

Japan’s Mount Fuji is at risk of erupting, according to a new study analyzing the tectonoic effects of the deadly earthquake that struck off the coast of Japan in 2011. An eruption could threaten the lives of over 8 million people in Tokyo and nearby areas, as well as destroy roads and railways connecting some of Japan’s most populous cities.

Using what’s called “seismic noise” to create a kind of ultrasound image of disturbances in the earth’s crust, French and Japanese researchers found that the area where perturbations were the greatest after the 2011 Tohoku-Oki earthquake was under Mount Fuji, increasing pressure on a volcanic region that hasn’t erupted since 1707. That eruption was most likely caused by an 8.7 magnitude earthquake that struck near Osaka, 49 days earlier.

“Our work does not say that the volcano will start erupting, but it does show that it’s in a critical state,” Florent Brenguier, an author of the study and researcher at the Institute of Earth Sciences in Grenoble, France, told the Guardian. ”All we can say is that Mount Fuji is now in a state of pressure, which means it displays a high potential for eruption. The risk is clearly higher.”

Geological disturbances act like a shockwave that creates cracks in the rock, increasing the potential for an eruption, according to the study, published in Science earlier this month.

"Mapping pressurized volcanic fluids from induced crustal seismic velocity drops," Science.
Japan’s high-sensitivity seismograph, the Hi-net, is among the world’s densest and means the 2011 Tohoku-Oki quake is one of the best recorded.

The 3,776-metre volcano, the highest point on the main Japanese archipelago, has been classified as dormant, but geologists have been constantly monitoring it, especially after a 6.2 magnitude quake struck near Mount Fuji four days after the Tohoku quake. (The Tohoku was a magnitude-9 quake.) So real is the threat of an eruption that officials released an evacuation plan this year on how to remove 1.2 million people from directly surrounding areas.

The effects of an eruption, depending on whether lava is emitted or not, could be catastrophic. Although residents could be evacuated before lava reaches them, it could still destroy key transportation nodes near the mountain, experts say. Tokyo, the world’s biggest mega-city that is only about 80 miles (130 km) away, would likely be covered in volcanic ash that would cause buildings, roads, and other infrastructure to collapse as well as disrupt flights.

In 2012, researchers said that the mountain’s magma chamber pressure had risen to 1.6 megapascals, almost 16 times higher than the mount’s level when it last erupted. A professor from Ryukyu university has also warned that that an eruption could happen before the end of 2015.

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