Will Mount Fuji Ever Blow Its Top?

Five huge explosions rattled the magma dome below Mount Fuji on Thursday as part of an experiment to glean insights into when Japan's most famous volcano might erupt again.

The underground blasts, each of 1,100 pounds of explosives, triggered mini earthquakes that will help scientists map the magma bubbling beneath and help gauge the likelihood of an eruption, said Keiji Doi of Tokyo University's Earthquake Research Institute.

"This is very important research," he said. "When the next eruption will happen is very difficult to forecast, but for these 300 years we've been waiting and waiting."

Snowcapped Mount Fuji is listed as an active volcano with a moderate risk of eruption. It last erupted in 1707, sprinkling Tokyo with ash.

An estimated 12.5 million people - roughly 10 percent of Japan's population - live near the mountain. A government report issued last year said another eruption could spew lava, ash and smoke over hundreds of square miles, disrupting roads and trains and causing up to $21 billion damage.

For towns like Fujinomiya, at the base of the mountain, results from Thursday's tests are key to improving disaster prevention plans, city spokesman Masakazu Takada said.

Doi said the experiment went well, but that it would take months to analyze the results.

He said there are no signs of an imminent eruption. But since October 2000, scientists have detected a sharp rise in the number of low-frequency quakes near the mountain which they say could indicate possible underground volcanic activity.

Thursday's pre-dawn detonations, buried 265 feet underground, were aimed at shedding light on the rumblings, Doi said.

Waves from the artificially induced quakes will help chart the volcano's underground structure, including pressure points of congealed magma and likely paths that magma might take if an eruption were to occur.

Sixty researchers from some of the nation's top universities have been doing similar tests on other volcanoes in Japan since 1994.

But these were the first such tests on Mount Fuji - the cone-shaped national symbol immortalized in poetry and woodblock prints for centuries. The volcano is Japan's tallest peak at 12,385 feet. It lies about 70 miles southwest of Tokyo.

Scientists have also staged blasts to study a fault in western Japan where an uncharted earthquake zone was linked to the 1995 Kobe temblor that killed thousands of people.

Earlier this year, researchers launched the world's first attempt to bore a hole into the red-hot core of a volcano, drilling into Mount Unzen in the country's southwest.

Such research is particularly important to Japan, which has 108 active volcanoes.

By Hans Greimel