No.36 Mount Fuji Scientific Research Institute

(Inagi Newsletter, October 15, 2014 issue)

On August 22, 2014, we visited the Fujisan Scientific Research Institute in Yamanashi Prefecture as part of a joint training session of the Tokyo Mayors' Association, where we listened to a lecture by Director Toshitsugu Fujii.
Mr. Fujii is a leading expert who obtained a Doctorate in Science from the University of Tokyo Graduate School, worked at the University of Tokyo Earthquake Research Institute, and has been the chairman of the Japan Meteorological Agency's Volcanic Eruption Prediction Liaison Committee since 2003.
The topic of the day was "The Formation of Mount Fuji and Its Impact on the Metropolitan Area Due to Eruptions." Mount Fuji was registered as a UNESCO World Heritage Site last June, and this facility was renamed from the "Environmental Science Research Institute" to the "Fujisan Scientific Research Institute" in April of this year. While the media and locals are in a celebratory mood, the theme of this event reminded us that this mountain is an active volcano.
An active volcano is defined not only as one that is currently exhibiting vigorous fumarolic activity but also includes those that have erupted in the last 10,000 years. It is puzzling to think that a volcano that has not erupted for 10,000 years is still considered active, but the Chaitén volcano in Chile, which erupted after 9,400 years without any warning, had a major eruption 27 hours after the first earthquake was detected, so we must remain vigilant.

It is said that Japan has 110 active volcanoes, which accounts for 7% of the world's total, making it one of the most earthquake-prone countries in the world. Among these, the volcanoes that could affect the metropolitan area are Hakone, Asama, and Fuji.
The one with the most immediate impact is Hakone, where a pyroclastic flow occurred during a major eruption 65,000 years ago, leaving a pumice layer of about 20 centimeters in some places in Tokyo. The most significant damage would come from Fuji, which had ash fall of about 2 to 10 centimeters in Tokyo during the Hoei eruption 300 years ago. While large volcanic rocks are unlikely to reach directly from Fuji, volcanic ash can accumulate over a wide area carried by the westerly winds.
It is concerning that, according to current knowledge, predicting an eruption of Fuji is difficult, but statistically, the only solace is that the probability of the next eruption being small is high.
Regarding the registration of Fuji as a World Cultural Heritage site, there are still environmental measures that need to be addressed, and neglecting them could lead to the possibility of cancellation of the registration. Among the issues pointed out, there was a need for an "emergency crisis management plan that functions in the event of an eruption or fire."
Since the Great East Japan Earthquake, we have been striving to eliminate unexpected events, but it seems that defending against an eruption of Fuji is quite difficult. However, it will be necessary to prepare for recovery after a disaster. The Inagi City Regional Disaster Prevention Plan has so far focused on measures primarily against earthquakes and wind and flood damage, but through this training, I felt that volcanic eruptions should also be a research topic in the future.