Government to permit the ocean disposal of volcanic ash in case of Mt. Fuji eruption

The Tokyo Metropolitan Area braces for a potential disaster- not due to an earthquake or typhoon, but a volcanic eruption from Mt. Fuji. As a precautionary measure, the government is considering ocean disposal of volcanic ash if a massive ashfall hits the capital, according to government sources.

If an eruption of Mt. Fuji were to occur on a similar scale to the 1707 Hoei eruption, the amount of volcanic ash cleanup required would be ten times greater than the debris cleaned up after the 2011 Great East Japan Earthquake, as per projections by the government’s Central Disaster Management Council.

An inclusion of this policy in the government’s guidelines on handling volcanic ash is planned to be compiled in spring 2024 or shortly thereafter.

Mt. Fuji, which has remained dormant for over 300 years since the Hoei eruption, is recorded as the longest dormant period in the past 5,000 years.

In the event of a significant eruption, it is predicted that the ash could reach as far as central Tokyo. The magnitude of the eruption is estimated to have spewed about 1.7 billion cubic meters of ash and other substances.

A recent analysis of the potential impacts of such an eruption was presented by the council in April 2020. In the worst-case scenario, rail networks in the Tokyo metropolitan area would be paralyzed three hours after the eruption, with up to 490 million cubic meters of ash needing to be removed. It would require about 1,000 units of heavy machinery to be deployed daily in cooperation with local governments concerned.

The upcoming guidelines will urge local governments to secure temporary storage and disposal sites for volcanic ash. Parks, playgrounds, and soil disposal sites are anticipated to be utilized, but the capacity of these sites may not be sufficient. Subsequently, ocean disposal is being considered as an alternative.

The marine pollution prevention law generally prohibits ocean dumping of waste, but an exception may be made in the case of an emergency, deemed necessary by the environment minister. Experts have indicated that ocean dumping of volcanic ash likely has little impact on the environment as it is naturally occurring, but the government plans to conduct tests to assess environmental impacts in preparation for potential ocean disposal.

In light of the looming threat, the government is set to engage in discussions with experts as early as January to address the potential risks and challenges associated with a possible eruption of Mt. Fuji. The recent announcements serve as a stark reminder of the ever-present threats posed by natural disasters, and the critical importance of proactive disaster management measures.


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