Eruption alert as Mount Fuji stirs

Of all the images associated with Japan, none is more famous than the pristine cone of Mount Fujiyama, the world's most beautiful mountain. On a clear evening, you can see it from Tokyo, gracefully silhouetted against the setting sun, and memorialised in countless photographs, paintings and wood-block prints. So timeless does it seem, you can easily forget that Fuji is still an active volcano. Easy, that is, until now.

Of all the images associated with Japan, none is more famous than the pristine cone of Mount Fujiyama, the world's most beautiful mountain. On a clear evening, you can see it from Tokyo, gracefully silhouetted against the setting sun, and memorialised in countless photographs, paintings and wood-block prints. So timeless does it seem, you can easily forget that Fuji is still an active volcano. Easy, that is, until now.

In Tokyo this week a group of scientists is meeting to consider the unthinkable: that, 300 years after its last eruption, Mt Fuji might again be stirring. They emphasise that a full-scale eruption, raining ash and volcanic rocks on Tokyo, is still very unlikely. But the evidence shows that, deep beneath the volcano, something is going on.

In an average year, 10 earthquakes occur beneath Mt Fuji, most of them too small to be noticed by anything other than the most sensitive machines. But last year the seismic activity began to increase sharply. In September, there were 35 low-frequency earthquakes, rising to 133 in October, 222 in November and 144 in December.

The rate declined to 36 last month, and all the tremors were as deep as nine miles below the surface. But one thing is clear. "It means that there is movement of magma down there," Shigeo Aramaki, a vulcanologist at the University of Tokyo, said. "It is a serious sign, but we don't know where it is moving or where it is going."

Mt Fuji is only 60 miles from Tokyo and in 1707, the last time it erupted, 850 million cubic metres of ash rained down on the city over the course of a fortnight. Local officials, especially those responsible for the 2.5 million tourists who visit the mountain every year, are stressing the unlikeliness of a repeat eruption, at least in the foreseeable future. But in June, the local government will mobilise 14,000 people in the first evacuation drills based on an imagined eruption.

The past few months have seen unusually frequent activity in the so-called "Ring of Fire", the seismically active region around the Pacific Rim. Two Japanese volcanoes erupted last year, forcing the evacuation of tens of thousands of homes. Mt Merapi in Indonesia and Mt Mayon in the Philippines are erupting now.