Mt Fuji eruption scenario to be studied

From this summer, the council will consider how to evacuate residents, and discuss ways to forecast and announce the range and amount of volcanic ash fall and the establishment of ash-related criteria for beginning evacuations.
Since the 3,776-metre Mt Fuji, which straddles Shizuoka and Yamanashi prefectures, took its current form about 3,200 years ago, there are said to have been seven large-scale eruptions.
 In the Hoei eruption that occurred on the southeastern flank of Mt Fuji in 1707, volcanic smoke is said to have reached as high as about 20,000 metres and volcanic ash accumulated at a depth of more than 3 metres in areas around the mountain.
It has been recorded that volcanic ash piled up to a depth of more than 10 centimetres in present-day eastern Kanagawa Prefecture, in areas including Yokohama and Sagamihara, and reached about 4 centimeters in areas around central Tokyo.
If a huge amount of volcanic ash falls on modern cities, it could land on electric transmission facilities. Rain could then cause short circuits, which could lead to large-scale blackouts. Since operation of railways, aircraft and vehicles would become difficult, it is highly likely that urban functions would become paralysed.
Some houses could also collapse due to the weight of the ash, and it would become impossible to use water and sewage systems for a long period of time. For these reasons, residents would need to evacuate.
The Japan Meteorological Agency currently issues volcanic ash fall forecasts for mountains including Mt Sakurajima in Kagoshima Prefecture, and Shinmoedake, a volcano that straddles Miyazaki and Kagoshima prefectures.
However, the agency simply urges residents to refrain from going out or driving a car when 1 millimetre or more of ash is expected, and does not assume a massive amount of ash fall that would require evacuation, as happened with the Hoei eruption.
A council comprising the Cabinet Office and nearby local governments, including Tokyo and three prefectures, created a volcanic hazard map for Mt Fuji, which shows via diagrams areas that could be affected by volcanic stones, lava flows, pyroclastic flows and other things, and calls for evacuation in case of an eruption on Mt Fuji. However, it does not include evacuations in the event of volcanic ash falling.
In the study to be started this summer, the government will ask volcanologists, officials from municipalities in the Tokyo metropolitan area and others to participate, and discuss methods for ash fall forecasts, the handling of forecast information, and measures to be taken by central government bodies, among other issues. 
Finally, the government will create criteria for what scale of eruption and ash fall should require evacuations to start.
In the fiscal 2018 budget, the government plans to allocate about Y183 million for promoting volcanic disaster prevention measures, and will use part of the budget for the planned study. The results of the study will be also used for measures for other volcanoes.
“When a volcano that has been inactive for more than 100 years becomes active again, it will lead to a large-scale eruption in several years,” said Toshitsugu Fujii, former chairman of the Volcanic Eruption Prediction Liaison Council and professor emeritus at the University of Tokyo. “Mt Fuji has been dormant for more than 300 years, and the government should take concrete measures as early as possible.”
Volcanic ash refers to cold fragments of magma each measuring 2 millimetres or less in diametre. It is a hyaline substance, and substances of volcanic gas are attached to it, so it can damage the eyes and throat. If an airplane engine takes in volcanic ash, it gets stuck inside, which sometimes causes the engine to stop. If it rains after volcanic ash falls, the ash becomes solid after drying out, which makes it difficult to dispose of it.