Experts warn that as many as 750,000 would evacuate if Mount Fuji erupts
Julian Ryall in Tokyo
Volcano experts have warned that as many as 750,000 people may be forced to flee their homes if Japan's Mount Fuji erupts.
The 3,776-metre mountain - which was recently added to the Unesco World Heritage list - last erupted in 1707, but it is still classified as dormant rather than being labelled extinct.
A panel of experts was set up by three local authorities that share the peak, prompted in part by the upcoming third anniversary of the Great East Japan Earthquake of March 11.
A draft version of the panel's report, which is due to be completed in the early part of next year, says that 470,000 people will have to be evacuated if more than 30cm of volcanic ash settles on the ground. That figure climbs to 750,000 people leaving their homes if lava flows similar to the 1707 eruption occur.
Retired professor Shigeo Aramaki, who is on the expert panel, said there was a need for those living near Mount Fuji to be ready for a worst-case scenario, although he said it was notoriously tricky to predict significant seismic movements.
"A very large-scale disaster has a very low probability, although smaller-scale incidents will occur more frequently," he told the South China Morning Post.
"But this just goes to show that we cannot trust the science of seismology, especially after the events of March 2011."
That earthquake had an immediate impact on Japan's most famous mountain - a magnitude 6.2 earthquake was recorded on the southern flanks of the mountain just four days later, Aramaki said - although the longer-term impact is unclear.
What is evident is that any disaster similar to the 1707 eruption would potentially cause havoc. Rail and road connections to the south of the mountain that link Tokyo with Nagoya, Osaka and the west of Japan would almost certainly be severed by pyroclastic flow, the experts believe, while flights would be affected by all the ash emitted from the eruption.
Should a Volcanic Explosivity Index reading of level five occur, the experts predict, Tokyo would once again be smothered in ash, buildings would collapse under the weight and infrastructure would be severely damaged by lava flows.
It would take weeks for services to return to normal, they warn, and the cost would run into trillions of yen.
Aramaki said the magma chamber of the volcano was being closely watched as this could serve as an early indicator that an eruption is imminent.
Some researchers have suggested that there is cause for concern as the pressure in the chamber has risen to a level higher than it was in 1707.
"We are not able to accurately monitor the magma when it is deeper than 20km below the surface," he said.
"At the moment, it seems that there are no irregularities above that depth, but more than that we just do not know."