In 1707 Mount Fuji erupted. The disaster came on the heels of the Great Hōei earthquake, whose tectonic activity compressed magma deep within the mountain, causing a gigantic explosion that blanketed the area that’s now Tokyo with a vast amount of volcanic dust.
It’s safe to say things have changed a lot in Japan since 1707, though Mount Fuji remains an active but generally dormant volcano. That peace may soon be shattered, as vulcanologists have reported that the internal pressure inside the magma chamber is rising steadily and the chances of an eruption increase each day.
Unlike 1707, the area in the Mount Fuji disaster zone now includes Tokyo, one of the most densely populated cities in the world, and home to around 41 million people. While Tokyo isn’t in danger of waves of magma sweeping through its streets, it is squarely in Fuji’s firing line, and the Japanese government has begun issuing guidance and warnings to residents about what’s coming.
"Mount Fuji Eruption Precursor? M6.0 Earthquake Strikes Yamanashi, Taiwan at Risk?"?? pic.twitter.com/P1OMKgDSuT
— World War 3 (@Worldwar_3_) February 24, 2025
According to a new report commissioned by an expert panel appointed by the government, Tokyo is expected to be blanketed with 500 million cubic meters of volcanic ash over 15 days. There’s a four-stage set of guidelines for ashfall, with residents advised to remain indoors, but those living within a wooden-frame house must monitor the ash on their property and evacuate outside their residential area if it reaches 30 cm (12 in) in height, as the combined weight together with rain may bring down the structure.
The report also predicts that the ash will effectively destroy many key pieces of electrical infrastructure. If ash covers electrical transformers, they will short-circuit, shutting down trains and subways. There’s also a chance of widespread blackouts as power fails, and with such high potential for chaos, citizens have been told they need to be self-sufficient.
When ash begins to fall during a future eruption of Mt. Fuji, should you stay home or run away? Experts have compiled guidelines. https://t.co/9NT0Gf65vo pic.twitter.com/GlPoocRmRY
— The Japan News (@The_Japan_News) March 21, 2025
As such, all Tokyo households have been strongly advised to maintain a disaster preparedness backup consisting of 15 days of supplies. These would include food, potable water, basic medical supplies, torches, back-up batteries, face masks, and, ideally, some form of eye protection. Other problems remain, like the behavior of foreign tourists who don’t speak Japanese and may not grasp the seriousness of the situation, providing shelter to those whose homes have been destroyed, and ensuring that emergency vehicles can navigate ash-clogged streets.
Current estimates are that if Fuji erupted today, the financial cost to Japan would be in the range of ¥2.5 trillion (roughly $25 billion). It’s worth stressing that experts can’t know precisely when Fuji will erupt, only that the danger is high and it’s time to make contingency plans. If there’s a silver lining, it’s that Japan’s widespread earthquake preparedness should mean most people will be aware of how to behave if disaster strikes. Even so, when Fuji erupts, prepare for chaos.
Published: Mar 27, 2025 1:26 PM UTC