Fuji shaken but not stirred by volcano tests

Five massive explosions rattled the magma dome below Mount Fuji yesterday as part of an attempt to discover when Japan's most famous volcano might erupt again.

The underground blasts, each using 500kg (1,100lb) of explosives, triggered mini-earthquakes, which will help scientists to map the magma bubbling beneath and gauge the likelihood of Fuji blowing its top.

Keiji Doi, of Tokyo University's Earthquake Research Institute, said: "When the next eruption will happen is very difficult to forecast, but for these 300 years we've been waiting and waiting."

Mount Fuji is listed as an active volcano with moderate risk of eruption. It last blew in 1707, sprinkling Tokyo with ash. An estimated 12.5 million people, about 10 per cent of the population, live near the mountain, 70 miles south-west of Tokyo. A report last year said another eruption could spew lava and ash over hundreds of square miles, causing up to 2,500bn yen (£13.4bn) of damage.

For towns such as Fujinomiya, at the base of the mountain, results from yesterday's tests will be used to improve disaster prevention plans. Mr Doi said the experiment went well, but analysis of the results would take months. He said there were no signs of an imminent eruption. Since October 2000, scientists have detected a sharp rise in the number of low-frequency quakes near the mountain which they believe could indicate underground volcanic activity.

The pre-dawn detonations yesterday,264ft (80 metres) underground, were aimed at investigating those rumblings, Mr Doi said. Waves from the artificially induced quakes will help to chart the volcano's underground structure, including pressure points of congealed magma and likely paths the magma would follow if an eruption were to occur.

A team of 60 researchers from Japan's leading universities have been conducting similar tests on other volcanoes since 1994. But this was the first time they took on Mount Fuji, 12,385ft (3,776m) high and a revered national symbol. Scientists have also staged blasts to study a fault in western Japan where an uncharted earthquake zone was linked to the 1995 Kobe quake.