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All residents in the zone from Mount Fuji to Sagamihara, Kanagawa Prefecture, just west of Tokyo, should evacuate in the event of a major volcanic eruption at Japan’s tallest peak, an expert panel said.

That area, which would receive at least 30 centimeters of ash from a major Mount Fuji eruption, is considered the most dangerous on a four-stage classification scale, according to the panel organized by the Cabinet Office.

In most other areas, residents would be urged to remain at home since electricity, transportation and communications would likely be severely hampered, according to the panel’s evacuation guidelines compiled on March 21.

About 180 eruptions of Mount Fuji have been confirmed over the past 5,600 years. The last major one affecting what is now Tokyo occurred in 1707.

In 2020, the government’s Central Disaster Management Council released its estimates for a major Mount Fuji eruption similar to the one about 300 years ago.

Eleven prefectures would be covered with volcanic ash, including 3 cm near Shinjuku Ward in Tokyo and 30 cm in the zone extending to Sagamihara.

The four-stage classification system is intended to be used in other areas where a potential eruption could occur, such as Mount Usu in Hokkaido, Mount Asamayama, straddling Nagano and Gunma prefectures, and Mount Aso in Kumamoto Prefecture.

Residents in stage 4 areas should flee to safer areas, according to the guidelines.

Those in stage 3 areas, which are projected to receive between 3 and 30 cm of ash, should be aware that ash accumulated on roads could disrupt transportation and prevent deliveries of adequate supplies.

Stage 3 residents should be prepared to store food, water, toilet paper and other supplies that can last for at least one week, the panel said.

Yosuke Miyagi, a researcher at the Research Division for Volcanic Disasters at the National Research Institute for Earth Science and Disaster Resilience, noted that volcanic ash is fine and light and can be carried great distances by the wind.

“The ash is hard as well as sharp because it contains glass particles, so if an attempt is made to clear a car windshield using wipers, the glass could be damaged,” he said. “The cornea could also be damaged if the ash gets into one’s eyes.”

Miyagi also warned that inhaling the ash could worsen the symptoms of people with respiratory illnesses.

If moisture is mixed in, the ash could become sticky, and even 10 cm of ash could render four-wheel drive vehicles inoperable.

Railways are especially vulnerable because even a few millimeters of ash on tracks would stop train operations, bringing public transportation in the greater Tokyo area to a halt.

East Japan Railway Co. has 44 vehicles with brushes to clear tracks, but it is not known if the equipment would be of use after a volcanic eruption.

Electric power could also be hampered if volcanic ash should become entrapped in filters at thermal-powered plants. Blackouts could occur if ash mixed with moisture accumulated on power lines or poles.

Another major concern is cleaning up the ash.

According to one estimate, a major Mount Fuji eruption would produce about 490 million cubic meters of ash, about 10 times the amount of debris that resulted from the 2011 Great East Japan Earthquake and tsunami.

The latest guidelines call for prioritizing the removal of about 31 million cubic meters from major roads and railway lines.

The guidelines call for authorities in jurisdictions where the ash has accumulated to store the removed ash.

But the Tokyo, Kanagawa and Yamanashi prefectural governments have only secured about half of the needed public space to keep the ash.

One Tokyo metropolitan government official said it would take decades to remove the ash if it all had to be stored within Tokyo’s borders.

(This article was written by Shiori Tabuchi and Shoko Rikimaru.)

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