As concerns rise over the dormant state of Mount Fuji, Japan's highest peak, officials are taking steps to prepare for the potential threat of a major volcanic eruption—one that hasn't occurred in over three centuries. Mount Fuji, standing tall at 3776 meters, has a lengthy history, with its last significant eruption recorded in 1707, which lasted for 16 days and resulted in volcanic ash swirling up to 23 kilometers into the atmosphere. The authorities are now bracing for a possible repeat of that disaster with new guidance aimed at the 44 million residents of the densely populated Kanto region.
On March 21, 2025, the Japanese government released a crucial response plan to address the implications of an eruption, laying out protocols designed to mitigate risks associated with volcanic ash. This marks a significant first step; it is the first time that an official plan has been prepared specifically for ash fallout from Mount Fuji.
The expert panel, commissioned by the Japanese Cabinet Office, issued their recommendations amid fears that in the worst-case scenario, a large eruption could deposit more than 30 centimeters of ash over Tokyo and neighboring prefectures, disrupting life and infrastructure for many—possibly for weeks to come.
In their report, the panel emphasized the critical importance of preparation. They advised residents to stay indoors whenever possible, particularly during phases 1 to 3 of their proposed response strategy, where ash accumulation would be less than 30 centimeters. Only in phase 4, when the ash levels reach this tipping point, should residents consider evacuation due to the increased risk of structural collapse in wooden homes caused by the added weight of the ash combined with rainwater.
"We are urging residents to prepare a stockpile of emergency supplies, including food and water for at least two weeks," the panel stated, acknowledging the inaccessibility of goods once a significant eruption occurs. As they noted, the volcanic ash could disrupt supply chains significantly, leading to shortages of essential materials.
During the 1707 eruption, the ash deposited about 4 centimeters in what was then Edo, now known as Tokyo. The potential fallout from a new eruption could be even more severe. According to simulations, if a similar eruption were to occur today, the volcanic ash could rain down on not just Tokyo, but also 10 surrounding prefectures, potentially leading to train stoppages, road blockages, and large-scale power outages.
Evacuating all residents of the densely packed metropolitan area poses an insurmountable challenge. The expert panel indicated that it is practically impossible to manage such a large-scale evacuation quickly and effectively. "Given the high population density, full evacuation is unfeasible," they remarked. Instead, the plan suggests a phased approach to keep people indoors until ash accumulation reaches critical thresholds.
In recent weeks, town halls have witnessed increasing preparations for such possibilities. Emergency drills are becoming routine as local governments emphasize community readiness. They are stockpiling supplies and planning escape routes, taking cues from lessons learned during past disasters. Experts further stressed that Japan, which has not experienced a large-scale volcanic eruption in over a century, must remain vigilant and proactive.
In addition to planning for the worst, the panel's report also raised awareness about the damage ash can cause—even during less severe eruptions. Buildings, such as school gymnasiums typically used as evacuation centers, could suffer major structural damage. Many have pointed out that while Japan is known for its advancements in disaster preparedness, the potential for catastrophic impacts from volcanic ash remains an under-discussed issue.
Mount Fuji's last eruption left behind an estimated 490 million cubic meters of volcanic ash, 10 times the amount of waste created in the wake of the 2011 earthquake and tsunami disaster. Given these figures, residents in the shadow of the iconic peak are rightly anxious about the implications of a new eruption on their lives.
While authorities have implemented these precautionary measures to protect citizens, they also emphasize that these guidelines do not indicate when Mount Fuji may erupt again or the magnitude of the ash fallout. The landscape of disaster preparedness is ever-evolving, and as scientists continue to monitor the dormant volcano, attention to its history and potential for activity is more pertinent than ever.
As a nation accustomed to natural calamities, Japan's response plan is a testament to the resilience and foresight of its people. However, the future of Mount Fuji in terms of volcanic activity remains uncertain, and as such, residents are encouraged to remain prepared, proactive, and informed about the risks that could arise from their beloved—yet potentially deadly—national treasure.
