Large raindrops began falling like sleet on the evening of May 29 near the Kagoshima prefectural office, creating thick, dark streaks on a white rental car parked nearby.

This type of rain is called “hai-ame,” meaning “ash rain,” and is well-known--and dreaded--by Kagoshima city residents. The ash comes from Sakurajima, Japan’s most active volcano.

The prefectural capital is so used to volcanic eruptions that the city could provide a model for the many ill-prepared areas around Japan, including near Mount Fuji, which hasn’t erupted for around 300 years.

The Cabinet Office has compiled evacuation guidelines for large-scale volcanic eruptions while the Japan Meteorological Agency (JMA) decided to introduce a volcanic ash advisory system.

Municipalities have been urged to prepare for eruptions.

In one government scenario, a Mount Fuji eruption would spew volcanic ash that reaches as far as the Tokyo metropolitan area, wreaking havoc on transportation systems and utilities that could affect millions of people.

The hai-ame that fell on Kagoshima on May 29 came about 20 minutes after Sakurajima erupted, according to the Kagoshima Local Meteorological Office. The volcano is located about 9 kilometers across Kagoshima Bay from the white parked car.

The plume rose up to 1,500 meters, and the small and light volcanic ash particles could travel great distances in the wind.

CONSTANT ERUPTIONS

Sakurajima, one of Japan’s 111 active volcanoes, erupted 146 times in May alone, far exceeding the total of 99 for all of 2024.

For Kagoshima city residents, volcanic activity has become part of daily life.

Local weather forecasts include wind directions over Sakurajima and expected ashfall zones, which residents use to decide whether to venture outdoors or hang their laundry outside.

About 5,500 roadside signs throughout the city display an image of erupting Sakurajima with the red kanji character meaning ash.

Residents can gather volcanic ash from their yards, place it into yellow ash collection bags and take them to “ash stations,” where they are picked up like garbage.

The city provides the free yellow bags, which measure about 30 centimeters square and hold 10 to 15 kilograms of ash.

To prevent traffic accidents caused by ash-covered roads, the city keeps around 100 road sweepers on standby. Featuring rotating steel brushes, these vehicles remove ash while moving.

Schools are equipped with underwater vacuums to remove ash that settles at the bottom of outdoor pools.

An outdoor water treatment plant in Kagoshima has installed covers over its filters to block ash intrusion.

“Sometimes so much ash falls that road lines disappear,” said Hiroaki Kuramoto, 48, a senior official at the city’s disaster management division. “But thanks to the countermeasures taken by the municipal government and private businesses, the ash usually doesn’t interrupt residents’ daily life.”

ASH FROM 1914 ERUPTION REACHED SENDAI

Yet not everyone fully understands the difference between Sakurajima’s routine eruptions and a large-scale eruption.

“Even some Kagoshima residents can’t distinguish between the two,” a city official said. “The level of urgency each resident feels varies.”

According to the JMA, a large-scale eruption lasts for more than 30 minutes and creates a volcanic smoke plume rising more than 10,000 meters above the crater.

Ash from such an eruption can cover an extremely wide area depending on the wind direction.

One example is the 1914 eruption of Sakurajima, which is considered the largest in Japan in the 20th century.

Lava flows connected Sakurajima island with the Osumi Peninsula. The ash plume was estimated to have risen 18,000 meters above the crater on the southern main island of Kyushu.

The volcanic ash reportedly reached Tokyo and even Sendai in northeastern Japan.

If a similar eruption were to occur today, an estimated 1 meter of ash could accumulate in the downtown districts of Kagoshima city.

The city assumes the magma volume might be the same as the flow from the 1914 eruption. Since 2018, the city’s disaster prevention plan includes a scenario in which large amounts of ash and pumice stones accumulate in city area.

Kagoshima plans to offer evacuation support to neighboring municipalities. It has divided areas on the opposite shore of Sakurajima island into six zones.

This spring, the city also established a research center that uses computer simulations to mitigate hazards from Sakurajima eruptions.

MT. FUJI PREPARATIONS

On June 22, Shinmoedake in the Kirishima mountain range straddling Miyazaki and Kagoshima prefectures erupted for the first time since 2018. The JMA is monitoring for signs of a larger eruption.

But it is difficult to predict when and where the next volcano in Japan will erupt.

The last time Mount Fuji erupted, in 1707, 30 cm of ash accumulated in Isehara, Kanagawa Prefecture, which is 50 km away from the crater, and 8 cm in Ichihara, Chiba Prefecture, 120 km away, according to the Cabinet Office.

A similar eruption today could block sunlight over downtown Tokyo in one to two hours. And just 0.1 millimeter of ash could halt train operations and cause widespread disruptions to electricity and water supplies.

The Cabinet Office’s evacuation guidelines advise people to stay in their homes, in principle. However, evacuations will be advised if ash levels exceed 30 cm. Such an accumulation, especially if rain is added to the mix, could cause wooden houses to collapse.

The JMA’s new alert system issues advisories for ashfall between 0.1 mm and 3 cm, and warnings for 3 cm or more.

The Tokyo metropolitan government revised the volcanic section of its disaster plan in late May, designating priority roads for ash removal.

East Japan Railway Co. (JR East) has also developed a brush device that can be attached to its inspection trains to remove ash from rails. JR East had deployed 41 of the devices across Tokyo as well as in Kanagawa, Nagano and Gunma prefectures as of June.

“We don’t yet fully understand the consequences of massive ashfall in a city with complex infrastructure and logistics,” said Masato Iguchi, 67, director of the newly established disaster-mitigation research center in Kagoshima and professor emeritus at Kyoto University. “We need to imagine what the social and economic impact would be and prepare accordingly in every region.”